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Paper No V Paper Code BOT521 Topic Taxonomy and Diversity of : & Angiosperms

Dr. Sahanaj Jamil Associate Professor of Botany M.L.S.M. College, Darbhanga

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed

UNIT- I

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

Classification of Gymnosperms. # Robert Brown (1827) for the first time recognized as a group distinct from angiosperm due to the presence of naked . BENTHAM and HOOKSER (1862-1883) consider them equivalent to dicotyledons and monocotyledons and placed between these two groups of angiosperm. They recognized three classes of gymnosperm, Cyacadaceae, coniferac and gnetaceae. Later ENGLER (1889) created a group Gnikgoales to accommodate the giankgo. Van Tieghem (1898) treated Gymnosperm as one of the two subdivision of . To accommodate the fossil members three more classes- Pteridospermae, Cordaitales, and where created. Coulter and chamberlain (1919), Engler and Prantl (1926), Rendle (1926) and other considered Gymnosperm as a division of spermatophyta, Phanerogamia or Embryoptyta and they further divided them into seven orders: - i) Cycadofilicales ii) Cycadales iii) Bennettitales iv) v) Coniferales vi) Corditales vii) Gnetales On the basis of wood structure steward (1919) divided Gymnosperm into two classes: - i) Manoxylic ii) Pycnoxylic

The various classification of Gymnosperm proposed by various workers are as follows: -

i) Sahni (1920): - He recognized two sub-divison in gymnosperm: - a) Phylospermae b) Stachyospermae

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

ii) Classification proposed by chamber lain (1934): - He divided Gymnosperm into two divisions: - a) Cycadophyta b) Coniterophyta

iii) Classification proposed by Tippo (1942):- He considered Gymnosperm as a class of the sub- phylum pteropsida and divided them into two sub classes:- a) Cycadophyta b) Coniferophyta

iv) D. D pant (1957): - He recognized three divisions, nine classes and seventeen orders of gymnospperms.

v) Cronquist, takhtajan and Zimmenmann (1966):- They placed gymnosperm in the division pinophyta of the sub-divisions embryophyta. Pinophyta was divided into three sub-divisions and six classes: -

vi) Bierhorst (1971): - he recognized three classes and clever order in gymnosperms. These are as follows: -

Gymnosperm

Cycadopsida Coniferopsida Genetopsida i) Pteridospermales i) Cordaitales i) Ephedrales ii) cycadales ii) coniferales ii) Gretales iii) Cycadeoidales iii) taxales iii) Welwitschiales iv) iv) Ginkgoales

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

Taylor (1981) was of the opinion that inspite of long study and refinement in techniques, classification of gymnosperms is still a subjective exercise. He proposed the following, classification where gymnosperms were divided into six divisons :-

Division i) progynomospermophyta ii) Pteridospermophyta

Order 1. 2. 3. 4. Calamophytales 5. Caytoniales 6. Corystospermales 7. Peltaspermales 8. Glossopteridales

Division III III. Cycadophyta

Division IV

IV. Cycadeodophyta V. Ginkgophyta VI. Coniferophyta Class 1) Cordaitopsida 2) Coniferopsida Order 1) Voltziales 2) Coniferales 3) Taxales

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

UNIT- II

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

Salient features and phylogeny of following fossil orders:

(a.) CAYTONIALES (b.) (c.) CORDIATALES

(a.) CAYTONIALES

Although, the caytoniales are perhaps most logically grouped with cycadofilicales, they represent a distint advance over the latter morphologically and are much more ancicent geoglogically. They can be regarded as derivation of seed which have advanced to a semiangiospermic level of development from the only. In the year 1925, Dr. Hamshaw Thomas brought the attention of botanists to a group of seed plants from the middle Jurassic of Yorkshiye coast which presents some remarkable features. From constomacy of association and similarty of cuticular strs, he was able to show that certain , microsporophylls and seed bearing organs belonged to one and the same plant. A great deal of microscopical details was visible after microtome section were cut. Caytoniales conists of leaves- Sagenopteris (S.phillipsi, S.halles, S.colpodes,&S.nilssoniana.) Microsporophyll or bearing organs- Caytonathus(C.arberi, C.kochi, C.oncodes, C.phillipsi ) seed bearing organ (Megasporophyll)

a) Cristhorpia b) Caytonia- (C.sewardi, C.thomas, C.nathorsti) The two yorkshine species of caytonia C.sewardi & C.nathorsti have been identified with sagenopteris Colpodes & S.phillipsi. The 3rd species caytonia Thomasi ( S.nilssoniana & microsporophyll caytonathuskochi) has been found in slightly older rocks in eastern green land.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

CLASSIFICATION: 1. D.D PANT (1954) Cycadophyta class. pteridospermopsida order. caytoniales family. caytoniaceae

2. Gangulle etal (1969) Pteridospermopsida Caytoniales Caytoniacea 3. Sporne( 1969) Cycadopsida Pteridospermales Caytoniaceae Caytonia

4. David.w.Bierhorst (1971)

Cycadopsida Caytoniales Caytoniaceae

STEM: It is a least known organ of the plant, tiny branched twigs with foliar buds, leaf scars of sageropteristype and “c” shaped leaf tissue are known. Internal structure of the stem represents the hard wooded shrub or a small . In no cases they were as thick as or tree ferns (Harris,1941).

LEAF: Specimens with one, two and three pairs of leaflets have been found fossilised. The leaf saganopteris phillipsi had a slendar petiole and four terminal

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

leaflets arranged in two pairs but not in whorl. The leaflets are lanceolate ranging from 2-6 cm in length and are borne palmately in group at tip of the petiole. The venetion of leaflet is reticulate. The leaflets had a well-marked mid rib and arched, forking lateral veins with lateral connections giving an anastomosing system like that of . Harris (1941) pointed out that both the whole leaf and the leaflet are often cut off clearly by Abscisson layer, a feature usually associated with dicotyledons.

MICROSPOROPHYLL or POLLEN BEARING ORGAN: The pollen bearing organ-caytoneathus was described as leaves under the name Antholithms belongs to same member of Grinkgoales. However, Thomas and Harris made it clear that in structure caytonathus was quite unlike anyother microsporophyll. It consists of a dorsiventral rachis bearing opposite or sub opposite pinnae. The pinnae branched irregularly and each terminal branchlet bore a single sporangium. The synangium

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

contains winged pollen. Each synangium had three or four loculi. On dehiscence the four pollen sacs separated from each other longitudinally except at the tip, where they still remain joined together.

SEED BEARING ORGAN or MEGASPOROPHYLL The megasporophyll shows haplocheilic type of stomats, an ordinary palisade and a transversely elongated transfusion or tissue which seems to occur where veins are rather distant. The stomatal subsidiary cells show from their relative position that they have independent origin (Haplocheilic) as in most gymnosperm and Angiosperm. Stomata distinguished from Bannettidales and Gnetales where the

Subsidiary cells are sister cells of guard cells (syndetocheilic) of seed bearing organs, Thomas described two Genera- caytonia and cristhopia, but subsequent workers have merged then into the one genus caytonia. The sseds were borne in a small like structures, which in turn were borne on a rachis some 5cm long. The rachis or stalk was strongly dorsiventrally, which tends to support to its interpretation as a megasporophyll. The term

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

cupule is applied to fruit like bodies enclosing the orthotropus . In C. sewardii there were about 8 seeds in each fruit as cuple in a single arched row, in C.nathorstii about 15 and in c. Thomasii about 30 in a double row. There is a lip or flanges situated close to the stalk. Between the ‘lip’ and stalk is a narrow mouth. In C. Thomasi and in others the lip is opened into the interior of the fruit. The lip was considered by Thomas as a kind of stigma on which the pollen grain germinated but it is now known that the pollen garin reached the microphyle of the seed. Angiospermy, therefore was only partly attained in caytonia. The integument is single and free from the nucellus. There is extra- ordinary thickness of cuticle covering the nucellus. There is no evidence of any vascular system in the integument.

SEEDS: 8-30 Seeds have been found per fruit. Intergument is single and free from nucellus and the base. Seeds do not have micropylar beaks, these are known as amphonespermum.

POLLINATION: Harris (1947) supposed that there was a drop mechanism as in many living Gymnosperm The pollen grains, once trapped in the drop, floating up to the channels to the seed. It is possible that the bladders on pollen grains act as floating device.

PHYLOGENY: Before establishing any affinity for caytoniales it must be realized that the plants are imperfectly known. The entire plants have never been discovered stem is very imperfectly unknown and anatomical details of vegetative and reproductive organ is also not available. is completely unknown and same with gametophyte. Therefore, any conclusion in the absence of these vital organs lead to erroneous concept.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

Caytonioles resemble most with

A. Pteridosperms particularly in : 1. Seeds structure similar to Conostoama And Gnetopsis. 2. Male similar to Crossotheca but in arrangement of anther there is a great deal of difference. 3. Form of leaf particularly 4 leaflets on a single petiole has been said to be similar to Marsilia which is considered to be the progenitor of pteridosperm.

B. Affinities with Bennettitales:

Caytoniales resemble bennettitales also – 1. Anatomy of ovules and presence of several layers (blown off layer) as suggested by Wieland (1975). 2. Absence of integumentary vascular system is the same in the cases. Though similarities in testal structure, are significant point relationship between caytinioles and bennettitales, there are many difference also: - 3. Manner of attachment of ovules, pollination mechanism and capule of the make them widely different. If there be any affinity between two groups, it must be remote.

C. Relationship with Gymnosperm:

1. The stomatal subsidiary cells are heplocheilic in origin which is a common feature of most gymnosperm and a few angiosperm (except Bannettitales & Gnetales). 2. Like cycades, and familiar mesosoic gymnosperm, in caytonia also the wall of marginal guard cell slightly envelope the wall of the subsidiary cell. 3. The pollen grains of caytoniales resembles externally very much to the pollen grains of pinus. In both cases pollen grains are winged. Pollen resembling caytonioles is today found only in Abietiueae and Podocarpacae. Different but related types of BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

wings occur in the Paleozoic conifers and cordaitales. But no body suggests that the caytonials has affinity with any of these. 4. The megasporophyll is pinnate like pteridospermales. 5. The seed structure is of purely on gymnosprmous pattern pattern except in the distribution and cuticle. 6. Pollination is of gymnospermous nature, krausel (1726) has confirmed the view much earlier.

RELATIONSHIP WITH ANGIOSPERM: The following angiospermic features shared by the caytonials are worth mentioning.

i) Like dicots, the whole leaf and even separate leaflets are cut off clearly by Abscisson layer. ii) The subsidiary cells of the guard cell is haplocheilic in origin as in some angiosperm. The guard cell is just as in the mesophytic vicia faba. iii) Thomas believed that the synangium of cytonanthus was a point of agreement with the angiospermic stamen despite its radial symmetry and the lack of filament and connective. iv) The closed carpol of caytonia is comparable to the closed carpel in Angiosperm. The flanges on the fruit of caytonia were considered as stigma And the fruit itself a kind of carpel. (Thomas) v) The distribution of cuticle in the seed is quite similar in both the cytonials and angiosperm. Botanists have suggested that caytonials may represent a starting point from which the evolution of the angiosperm start. In spite of much similarities the single point of difference is the direct entrances of pollen grain up to the ovule which is of vital importance out with all the possible relationship of the group with angiosperm and that it only guides us towards making an approach to such question but does not solve themselves.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

CONCLUSION: The relationship of Caytoniaceae is not at all clear, and it appears to be quite isolated. Few fossils have created such a stir among morphologist as Caytoniaceae when it was first discovered (Thomas 1925). He emphasized similarities with both pteridosperms and angiosperms. He assumed that it provides a clue to the origin of flowering plants. He considered the flange on the cupule as a stigma, the cupule itself as a kind of carpel and the synnangium as the angiosperms stamen (despite its radial symmetry and lack of a filament and connective). However, the pollination in caytonia is still at the gymnosperm level (Harris, 1964). Thus a decision on its phylogenetic relationships should be taken on after we know more about the nature of its cupule (sporne 1965).

(b) PENTOXYLALES

INTRODUCTION: Prof.B.Sahni (1948) published a paper in the new group “Pentoxylae” in Bot. gaz.110,47-8. This group was discovered from village Nipani in Rajmahal hills in Santhal Pargana and this group comes from Jurassic of India. The existence of group was illustrated in 1928 and name Pentoxylae was proposed in 1948. Dr., Ravi, prof Srivastava and Prof. Sahni are its discoverers.

The name Pentoxylae has been given to an associate structure of stem, leaves, seed bearing and microsporangiate organs. All these parts of Pentoxylae are known from rajmahal hills of india. This group of Pentoxylae has affinities with Cycadales, Bennettitales and Coniferales (Lam 1952) Most part of materials are silicified but some impression have also been found. Sporne (1965) has treated this group under the name “Pentoxylales”. Harris (1962) also discovered some member (carnocomites cranwelli) of this group from New Zealand. B.P.srivastava (1946) and Vishnu Mittre (1953,1957) are some of the major Indian contributors on Pentoxylales.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

GENERAL ACCOUNT:

Reconstruction of the group “Pentoxylae” was made by Sahni by setting different parts and various names were given to these different parts. Harris (1962) reported the fossil remains of this group from New Zealand. 1. The plants were probably shrubs or small . The habit is not known but the size and diameter of the stem, its branching and leaves reflects upon its shrubing or trees like habit. 2. Stem- form genera Pentoxylon sahnii Nipanioxylon guptii a) Pentoxylon sahni ranged in size from 3mm to 2cm across. b) The branches are of two types: i) Long shoots ii)Dwarf shoot c) Stem bears rhomboidal leaf scars and spirally arranged simple leaves are restricted to the dwarf shoot. d) The stems were polystelic with 5 or 6 primary stele hence the name “Pentoxylae”. Each stele has its own complete ring of cambium.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

MODE OF OCCURRENCE:

The greater part of its material is silicified and well preserved, but there are also impressions and petrifications found near the village Nipania in rajmahal hills(Bihar), near dumarchir in Annapara. The plant bearing formations is called Rajmahal series of Gondwara divonian – a constituent of Mesozoic vegetation.

DESCRIPTION:

It is remarkable group of Gymnosperms showing a combination of characters typical of Bennettitales, Cycadales & Coniferales and at the same time possessing a certain unique features of its own, not so far known in any other group of Gymnosperms. For this new group the name Pentoxylae and the type genes Pentoxylon is proposed. Our knowledge of the Pentoxylon is confined to: i) The leaves, named Taeniopteris spatiedates, but now called Nipaniophyllum with 2 species:- N.ravi and N.hirsutam ii) The stem segregated into two distinct but closely allied genera- Pentoxylan sahnii & Nipanioxylon guptii. iii) The female cones, carnoconites with two species: - C.compactum & C.laxum. iv) The male flower recently described by Vishnu-mitra as sahnia Nipannienis and reported by R.rao (1953) in Palebotanists= vol.2(75-84), under the title “ A male flower of Pentoxyleae with remarks on the structure of the female cone of the group”. After different correlation of the various plants into one, it appears that two distinct members of Pentoxylae were present in Rajmahal series. 1. The plant bore female cone of cornoconite compactum type. The main stem was Pentoxylon sahni with young shoots and foliage of the Nipaniophyllum raoi type

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

2. They bore female cones of Coroconite laxum type. The main leaf was N.hirsutum and the stem of Nepanioxylon guptii type.

STEM:

The stem Pentoxylon is characterized by following: i) Stems attains columnar, slender, several cms in diameter and contains 5-7.5 mm thick short shoots closely aggegrated stele & hence the name Pentoxylon, rarely 6 steles (responsible for generic name). ii) Pr. Xyulm (wood) is strongly endocentric in its development and so tangentially elongated strands of primary wood are enclosed by sec. wood. It means that most of the cambial activity takes place on outer side of these vascular, strands. iii) Xylem was probably mesarch. iv) The small peripheral vascular bundles have no leaf trace and their nature is unknown. v) The wood structure is type. It consists of tracheids and small uniseriate medullary rays. The tracheids have one or more rows of circular and bordered pits on radial wall. Medullary rays are 2-7 cells in height. Wood parenchyma and resin canals are absent. vi) Sclerotic nets are abundant in the cortex but they may be present a few in number in pith portion. vii) There was a separate mass of sec. wood with well-marked annual rings which was more developed towards the center of the stem than to outward direction. One to two annual rings have been marked. This occurrence suggests that growth has been ceased in the stem when one or two annual rings have been formed (i.e. 2ears growth). Another stem genus nipanioxylon shows:

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

i) 7-9 very small collateral steles. The steles are distantly placed ground the large side pith. ii) Such steles have no growth rings. iii) Endocentric growth less strongly developed. iv) Wood is pycnoxylic and is without parenchyma i.e. like Pentoxylon Wood parenchyma is totally absent. v) The stem has branch 5.7 mm thick which are croweded with closely aggregated leaf cushion.

LEAVES: Leaves are known as “Nipaniophyllum” Sahani(1947) reported thin leaf as a petrified species occurring at Nepanio(vill). Leaf has following important features: i) Leaves are strap shaped, leathery varying in length from 7-10cm and breadth 1cm. ii) The apex of the leaf is either acute or rounded. The lamina is narrowing gradually to form a narrow wing at the petiole. The mid-rib is 1 mm broad and parallel nerves persist upto the apex. The lateral veins come out from the mid-rib at the angle of 90 and they are either unbranched or forked once to form loop like expansion. iii) V.bs. in the petiole and the mid-rib are 5-9 in number; placed in a shallow curve and being diploxylic in nature cycadean type. iv) Stomata haplochelic, subsidiary cells are 4-6 in number encircling the guard cells. They are confined only to lower surface of leaf. Leaf cuticle is thick. Scalariform tracheids are present in the vascular system of leaf. v) Leaves are deciduous. There was formation of abscission layer. vi) No transfusion tissue has been seen. Hydathodes like opening at the tips of lateral veins are as like the chalk glands of the modern ferns. vii) Epidermal cells have sinnous walls different from cycades and Bennettitales, sinnousites being more pronounced on lowert epidermis.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

MALE STROBILUS: The male strobilus sahania-nipaniensis is a male flower. They were borne terminally on the dwarf shoot. They consisted of spirally arranged filiform appendages which are used at the base to form a disc. Unilocular sporangia were attached on short branches of these filiform appendages. Pollen grains are boat shaped with a single long furrow which is narrow at the end and wide, open in middle. Wall is smooth.

FEMALE CONE:

They are known as carconites of inflorescence is divided into several branches or pedicels each of which terminates into a cone. Cone axis contains a ring of 5 V.strands and bears several compact seeds. In C.Compactum: i) Strobilus contains several ovules. ii) The micropylar part of each ovule faces towards fumile and ovules are well developed.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

iii) Interseminal scales are absent. iv) Ovules have thick integument being differentiated into stony and fleshy layer. In C.laxum: i) Large number of smaller ovules with less developed fleshy layer. ii) Nucellus free in the ovule down to the base. iii) 5 V.bs. in a ring in the cone axis and so in a TLS the cone axis appears 5 angled. iv) Single vascular supply the chalazal end of the ovule.

AFFINITIES: The phylogenetic status of pentoxylales has remained a fascinating problem. Sahni (1948) described that at one hand leaves show a mixture of cycadean, coniferous and bennetittales features. The protostelic stems mark similarities with Paleozoic Medullosaceae.

RESEMBLANCES WITH CYCADOPHYTES:-

1. Similar leaf anatomy. 2. Diploxylic bundles in leaf traces. 3. Presence of haplocheilic stomata. 4. Furcate type of venation also found in ferns and in some modern cycads like in stangeria.

RESEMBLANCE WITH CONIFERS:-

They resemble conifers in possessing presence of: i) Pycnoxylic wood. ii) Tracheids with circular boardered pits, arranged in a uniseriate or biseriate manner. iii) Uniseriates wood rays and iv) Dimorphism in the stems of pentoxylon sahnii and several conifers. However, the general anatomy of stem of Pentoxylales is not

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

at all coniferous as mentioned also by sahnii(1948). Pentoxylales are totally stechyospermous while coniferles are partly phyllospermous and partly stechyospermous.

RESEMBLANCE WITH PTERIDOSPERMS: -

They resemble the pteridosperms family medullosaceaein having a polystelic vasculature in their stems. The secondary wood of pentoxylon was pycnoxylic, character also encountered in some species of medullosa.

UNIQUE FEATURES OF PENTOXYLALES:-

The female infrustescence with a cone like organization and without any sterile appendages or megasporophylls is a feature unique to the pentoxylales.

RESEMBLANCE WITH BENNETTITALES: 1. Presence of syndetocheilic stomata in addition to haplocheilic is a Bennettitales character. 2. Dwarf shoots of Pentoxylon are similar to that of Bennettitales. 3. Diploxylic nature of the vascular bundles. 4. Whorled micro- sporangiophores. 5. Superficial resemblance between male of both groups. 6. The manner in which the ovules were borne in pentoxylales was similar to that of the bennettitales, however the inter seminal scales found in members of Bennettitales were absent in Pentoxylales. 7. Stachysporous nature of their male and female organs i.e. instead of leaves, these organs were borne on the stems. 8. Presence of direct leaf trance also brings the two groups quoite close to each other.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

However, the polystelic condition of the stems of Pentoxylon and Nipanioxylon has no similarity with that in Bennettitales. In pentoxylae, The sporangiophores were erect, radial structures without any sterile part. They were spirally branched and possessed sac like unilocular microsporangia. On the other hand in bennettitales these structures were completely different. They had circinate dorsiventral pinnate with a sterile and synangium bearing portion.

AFFINITIES WITH SOME OTHER GROUPS:

While stem dimorphism of Pentoxylon sahnii is a Ginkgolean feature are also a coniferous one, the diploxylic vascular bundles of Pentoxylales are also seen in cordoitales as also in Bennettitales. Meeuse(1961) observed several resemblances between Pentoxylales and Pandanus and opined that “Pandananceal and some related monocotyledon” have descended directly “from Pantoxylales”.

RESEMBLANCE WITH CYCADOPHYTES: 1. Possession of direct leaf trace in pentoxylae and seedlings of some cycads. 2. Leaf trace anatomy is showing diploxylic nature of their vascular bundles. 3. Haplocheilic stomata. 4. Vestigial polystely in the seeding stages of some modern cycades. 5. Nature of wood and pittings. 6. Possessing more or less similar kind of pollen grains and 7. Structure of their seeds and peduncles. However, vascular bundles in pentoxylon are not arranged in the cycadean manner. There is also no similarity between the polystelic conditions of pentoxylon and mature modern cycads.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

CONCLUSION:

The enigmatic group displays a unique combination of characters. The polystelic stems resemble some of the palaeozic medulloseceae. Yet the secondary wood is Pycnoxylic(coniferous). The leaves show both cycadean and cycadeoidean features in the leaf trace anatomy and stomata. Both the pollen and seed bearing organs are stachysporous. The microsporangiate organs morphologically resembles cycadeoids, and the pollen is cycadophyde. The ovulate cones are unlike any gymnosperm and their structure is peculiar to themselves. Most Palaeobotanists agree that this group should be given status to cycadeoidales and cycadales. Investigations during the last 30 (or more) years have not clarified the exact affinities of this group. According to (Rao 1981) at the present level of our knowledge, it cannot be referred to any known group of plants exclusively. It can only be regarded as an isolated synthetic group which shows a mixture of features in common with pteridospermales, cycadales, cycadeoidales and coniferales. The correct Phylogenetic placement must await further information.

(c) CORDAITALES

The cordaitales is a group of Paleozoic arborscent gymnosperms, which together with the seed, ferns, constituted the bulk of the seed plants of the coal forests. It is based upon the old genus cordaites, which was proposed many years ago by Unger for certain types of leaves and stems which are almost universally present in carboniferous plant bearing racks. The group extends from seronian through carboniferous upto the times and in India they had been found even in the lower Mesozoic, i.e. in lower strata of India. Scott and Soward, the most outstanding of modern English Palaeobotanists have classified them into three families: - 1. PITYEAE

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

2. CORDAITEAE 3. POROXYLAE

The pityeae embraces a group of genera founded entirely upon vegetative parts, mostly stems and trunks and the Poroxylene consists of one genus Poroxylon, which shows certain distinctive features in the structure of the stem. The original genus Cordaites, together with all vegetative and reproductive parts described under different names but believed related to it constitute the family cordaites. thus constituted the cordaitales is an artificial orderbased principally on anatomical feature of vegetative parts. The genus assigned to the poroxyleae, is now determined to be a pteridosperms, having its affinities with the callistiphyteceae (Rothwell, 1975a). PITYAE:

The Pityae are known only in the and the lower carboniferous and are therefore the oldest of the three families of the Cordaitales. Researches during the past three deccades have shown that as suspected the affinity of Pitys is with the pteridosperm (Long, 1963,1979) and that callixylon is a (Beck, 1960). By virtue of structural resemblance between the woods within the group seed production in the Pityae is inferred bit not proved. Seed like frutification have upon a few occasions been reported from the Devonian, but subsequent investigation have always shown them to be either bearing organs.

The most abundant and widely distributed genus of the Pityae is callixylon, which occurs throughout the entire vertical extent of the upper Devonian. In North America, it occurs in greatest quantity in the new albary shades of the Indians and in black shades of similar age in Ohio, Kertucky and Ontanio. Callixylon was a large tree. The trunk was tall and straight and bore a crown of slender branches at the top.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

CHARACTERISTIC FEATURES OF CORDAITALES: - MORPHOLOGICAL: The after reproduced reconstruction of a cordaite illustrates a tree presumably attained a height of 30m and a diameter of more than 1m at the flared base. The estimate of the height of these trees was obtained from permineralized trunks with wood of the cordaitean type ( seward 1919). The branches that formed the crown of the plant bore spirally arranged sessile leaves (fig). The shoots bearing the pollen and ovule forming fructifications were scattered among the leaves. According to an early reconstructions, the root system is depicted as being shallow and extending laterally for several meters. More recently, Cridland(1964) has reconstructed a cordaitean plant as a small tree about 5m high. This highly speculative reconstruction depicts that root system as being composed of stilt root not unlike those of mangroves.

ANATOMICAL STRUCTURES:

Researches conducted during the last four decades (Traverse, M50; Cohen and Delevoreyas,1959; Baxter,1959) suggest that there are two different types pf anatomically preserved cordaitean stems. Recent studies confirm that the stem type represents separate genera of whole plants (Rothwell, & Warner, 1984, Trivett & Rothwell, 1985, 1988; Trivets 1991). Cordaixylon is usually used for cordaitan stems showing pith and endarch primary vasculature including leaf and branch trees and wood. Mesoxylon designates similar stems with mesarch xylem maturation. The cordaitean trunk contains a large pith, a relatively small amount of primary wood and a thick layer of secondary wood. The transverse section of branch of Cordaixylon reveals a fairly large pith cavity surrounded by a band of Pycnoxylic secondary wood. The primary xylem strands are almost impossible to distinguish from the innermost cells of secondary xylem adjacent to the pith. Radial section through this region show

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

the innermost cells to be narrow protoxylem elements with spiral thicknings. There is a wealth of information about the leaf genus cordaites. (Seward 1919) has the literature relating to compression, impression fossils of cordaites upto the time. The most reliable characteristics for epidermal structures and internal anatomy (Harms & Leimen, 1961; Good & Taylor 1970). In their general internal anatomy most species of cordaites have a poorly differentiated palisade layer and a spongy mesophyll with a large number of composed of two layers of cells. The xylen of the vein usually has ab and adoxial development, but some lack centrifugal metaxylem the phloem, if preserved is located along the abdoxial surface of the xylem.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

REPRODUCTIVE STRUCTURES:

Both pollen and ovulate fructifications of cordaites are assigned to either cordoithanthus (fig 28.8D) or Gothania. These reproductive structures reffered to as strobili, inflorescence or cones are actually compound fructifications consisting of a primary axis that bears secondary shoots in the axis of modified leaves called . A few, near or at the distant end of the secondary shoot are fertile and terminate in pollen sacs or ovules. As far as is known the reproductive structures are strictly monosporangiate. Strobilus of Cordaitales:

The most recently investigated cordaiteen inflorescence in cordaianthus shulers from the middle Pennsulavanian coal- ball material (Devoryas 1953). The individual strobili are short, being only slightly more than 1cm long and one and half as wide. The strobilus consists of a short woody axis or dwarf shoot bearing spirally arranged overlapping appendages, some of which are fertile. The fertile appandanges bear terminal ovules or pollen sac, but never as far as known, both within the same inflorescence. The strobili of the male inflorescence contain one to six or more fertile bracts (microsporophylls) each of which supports as many as six terminal elongated pollen sacs. Each female strobilus usually contains 1-4 ovuliferous appandages (megasporophyll). In some species the megasporophyll are formed and bear two terminal flattened ovules. It is difficult to distinguish between them unless pollen sacs or ovules are present.

Until recently most of our knowledge of the internal organization of the cordaitean strobilus was based upon silicified French material from the late carboniferous.

The situation is well shown in cordaianthus fluitans and the afore mentioned. C.Shaleri, which bear their fertile appandages on the same spiral with the sterile ones.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

The pollen grains of Cordaites are globoid bodies usually measuring less than 100microns in their greatest dimensions. As with pollen grains and heavily walled generally, the wall consists of an intime and a heavily cutinized Exine. The exine is inflated into a single large air sac that completely surrounds the intime except for a small area at one side of the grain. This air sac rendered the pollen grain buoyant and fascilitated dispersare by wind. The pollen grain is essentially an anthoidium similar to that produced by modern gymnosperm.

Ovules of Cordaitales : In the ovules nucellus was completely separate from the integument. The integument formed a prominent nucellar beak and a large pollen chamber. There were two coat surrounding the ovules, outer thick and fleshy and the inner one delicate in young ovule but hard in older ovules. Both these coats were separate below but more or less united above. Dr. sahni recognized two groups of ovules according to their position.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

i) Phyllosperms: The ovules born on leaves as seen in Pteridosperms and cycas. ii) Stachysperms: The ovules as seen in Cordaitales, and Corniferales.

FERTILIZATION: It is probable that pollen tubes were produced vwhen the pollen germinated although fertilization was apparantely carried out as in recent cycades. Fertilization apparantely was accomplished by swimming sperms. There is no evidence of fertilization by a pollen tube in any Paleozoic seed. If a pollen tube was present, it probably functioned as an absorbative organ as in recent cycades and the Ginkgo. Seed - Cordaitean seeds vary considerabally in size although they seldom exceeds 3cm in their greatest dimension. The base of seed is commonly rounded or slightly cordaite and the apical portion in same is drawn out into a beak. The nucellar beak of the ppollen chamber

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

projects upward into microphyle. The resemblances between seeds of the pteridosperms and the cordaiteas is close.

AFFINITIES OF CORDAITALES: A. RESEMBLANCE WITH GINKGOALES:

Presence of probable mobility of the cordaites sperm and double leaf trees. The recent ginkgo exhibits a number of characteristics that may have been retained from some ancient form ancestral to both the Ginkgoales and the Corditeae. The motile sperms produced by the cycades and Ginkgo apparantely were shared by all palezoic seed plants but fertilization by means of pollen tube was probably a later development.

B. RESEMBLANCE WITH PTERIDOSPERMS:

Between the cordaites and the pteridosperms the similaritits are not as conspicious as the differences. The strongest bond between them is the structure of the seeds, which are not readily separable. There is little in common between the foliage of the two groups and numerous modifications would be required to produce a cordaitean leaf from the Pteridosperms frond. As to the anatomy of the stems a large pith is the rule in both groups. Poroxylon probably comes nearest to linking the pteridosprms and the cordaitales because it has like secondary wood double traces and exarch primary woods. Multiseriate boarderd pits cover the tracheid walls of the pteridoperms and most of the cordaites. Although the cordiatales and pteridosperms were nearly contemporaneous through out the later part of the Paleozoic era they differed remarkedly in habit and external appearance.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

C. RESEMBLANCE WITH CONIFERS:

The most apparent resemblances between the cordaiteae and the modern conifers is the lofty arborscent habit, a feature shared by the Pityeae and possibly also by Poroxylae.

The presence of multiseriate boardered pits on the tracheids walls and the absence of resin canals from the wood of the cordaiteae has long been looked upon as primafacie evidence that the cordaiteae are more closely related to the Araucerian conifers of the Southern hemisphere. These similarities coupled with the fact that wood showing araucarian characteristics is the predominating form of coniferous wood through out the Mesozoic, are mainly responsible for the prevailing views of araucarian antiquity and theories that the arancaurians are cordaitean derivatives.

RESEBLANCE WITH CYCEDOFILICALES:

Cyacadofilicades and cordatailes, both seems to be related to clear from their habitat the general form and structure of plants, the form of strobili especially male cone, structure and form of ovule and finally of seed was very primitive. In the two in the ovule of the two the presence of free nucellus.

The form of integument with two sets of lvascular bundles in it and the form of pollen chamber and lastly the absence of embryo are really primitive features which naturally present in the primitive groups. All these resemblances mean that either the cycadafilicales give rise to cordaitales or the cordaitales to cycadofilicales.

Evidentaly it must be some heterosporous pteridophyte which lived near about the Devonian might have given rise to cordaitales and cycadofilicales which is clear from the stem anatomy of cordaitales in which endarch siphonostele was more common.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

CONCLUSION:

Cordaitales is the oldest truly coniferophytic group of plants (miller 1977). We do not precisely know from what ancestral group the cordaitales evolved. The data indicate that the evolution of cordaitales from lower carboniferous seed ferns included several singnificant steps (Rothwell, 1986) such as: 1. The transition from hydrosperman reproduction (the most primitive type of reproduction in gymnosperm), where the ovules had a complex pollen chamber, (ehich seede the macrogametophyte with radial. Trilets exine structure) where the integument plays an active role in Pollination. 2. The vegetative leaves changed from the pinnately compound to strap shaped simple leaves with entire mergins. 3. Reduced number of ovules and microsporangia per microphyll. 4. Aggregation of on compound shoots. It is uncertain whether changes in anatomical features and cuticular anatomy were also instrumental in evolution of crdaitales.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

UNIT- III

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

General features, distribution, phylogeny and economic importance of following orders:

(a) GINKGOLALES

Ginkgoales is an ancient group which came into existence during the Permian, and achieved worldwide distribution; lxurians during the and Jurassic period of Mesozoic and began to vanish during and onward into coenozoic . the maximal diversity occurred during the middle Jurassic and remain have been collected from many countries: Alask, green land, scandinevia, Siberia, magnolia, England, Europe, china, japan, Australia, New Zealand, India, tip of south Africa and south and north America. Only ginkago owns its existence with greatly restricted distribution. It is confined mostly in south eastern china and japan. However, it is cultivated in Europe, USA. and India. In India it is confined mostly in Mussorie, Dehradun, Darjeeling and nainital.

CLASSIFICATION:- K.R SPORNE (1965) classified ginkgoales into families 1. trichopityaceae – extinct – trichopitys 2. gingkgoocera – extinct – bairea,

Aretobaria, ginkgoties, stephenophyllum , dicophyllum, and ginkangodium etc. Extanct: ( monotypic )

GINKGO

The ginkgo tree is an object of interest to scientist and layman. Its dichotomously veined, fan shaped leaves are unique among the tree of temperate climate. This feature, along with the production of motile sperms, and the terminally borne seeds constitute a set of primitive

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

characteristics that have earned for the tree the appellation of living fossils. Anatomically ginkago resembles recent conifers, its peculiarities being the double leaf trocus and the Lysigenous resin duet within the leaf tissue

The ovulate fructification of ginkgo is a rather indefinitely organised structure and abnormally developed specimens sometimes bear ovules on party developed leaves that are strongly reminiscent of the leaf borne seeds of certain pteriodosperms.

The venation of the gingko leaf is strictly dichotomous in some forms but approaches a sympodium in others. Between the veins the epidermal cells are polygonals in outline, but over the veins the cells are more rectangular or spindle shaped. These characteristics are believed adequate to distinguish the ginkngoles from other gymnosperms. The epidermal cell walls are slightly wavy but not as much as in the cycadeoids. The stomata are usually without defined orientation, although they are frequently in ill-defined rows. From four to seven subsidiary cells or a circle around each slightly sunken stomata. :- many authors consistently use ginkgoits for all fossil leaves resembling ginkgo even though they may be indistinguishable

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from the leaves of the living species, HERRIS FLORIN (1935) has proposed that ginkgoits be applied to gonkgo like leaves which may be distinguished from ginkgo by anatomical characteristics. BAIERA:- their genus ranges from hectic to the lower cretaceous. It possesses deeply cut leaves in which the central incision extend almost to the base. Less deep incisions divide the two lateral lobes into slendar linear segment each of which contain but two to four parallel veins. The leaf is petiolate, similar to that of ginkgo, but in some of the slender or the narrowing of the lamina continues so near the point of attachment that a petiole seems almost non existent.

OTHER GENERA:- there are several other Mesozoic ginkgolean genera that pussess long, slender, ribbon like, sessile leaves produced in clusters upon scaly dwarf shoot. One of these is sphenabaiere, which is the oldest ginkgoales being known from the late Permian, Florin ( 1949 ) investigated Trichopitys hetermorphs from the lower permian of southern France. It has spirally arranged dichotomously branched leaves without lamina.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

There are small branched ovulifeous usses in the axil. Each ultimate branch bears a terminal, recurved ovule, unlike ginkgo. The male organ of trichopitys are not known. However, sphenobaierafurcats bears clusters of microsporangiate the branches at tips of a befurcating axis, which are borne in turn in short shoot, along with leaves similar to trichopitys.

Ginkgo possess following characteristics peculiar in itself:- 1. Tall tree growing upto 100ft and have an excurrent habit 2. Deeply rooted – tap root system. 3. Fan shaped deciduous and bilobed leaves with open dichotomous venation. 4. Presence of long and dwarf shoot on the stem. 5. The plant is dioecious and slow growing 6. Pycnoxylic wood. 7. Catkin like male inflorescence that bear microsporangiophorous, each bearing 2-4 pendent microsporangia terminally. Microsporangia irregularly arranged on the axis. 8. Presence of lump like out growth at the tips of microsporangiophore.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

9. Ovules arise in group from the apices of dwarf shoot ( axillarly branches ) in the axil of scales or foliage leaves. 10. The presence of collar below the ovules. The ovules are borne terminally on long stalk or peduncles and there are no structure like a to the megasporophyll. 11. The female gametophyte is produced into a tentpole like structure at its apex 12. Top shaped spermatozoids are motile and bear a spiral band of cilia. 13. Embryo lacks a well developed suspensor. 14. The mature seeds are large, fleshly and about the size of a small apricot. The integument is three layered. The outer layer is fleshy, middle stony layer, inner fleshly watery layer. 15. The female gametophyte is green in colour due to presence of chloroplast in the cell.

A. RESEMBLANCE WITH FERNS: 1. Dichotomously veined leaves 2. Motile and multiciliated spermatozoid. 3. A distinct ventral canal cell in the archegonia. 4. Presence of helical and boardered pitted tracheids both in ginkgo and ophioglossaceae.

 Bierhorst(1971)suggested that motile sperms are resemblences between tracheidal transformation of Ginkgo and some like ophioglossum also suggest a remote origin from forms like an europhyps.

 Ophioglossaceae exhibits a coniferophytetransition from helical type of tracheids to the ultimate type with boardered pits.In this respect it resembles Ginkgo.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

B. RESEMBLANCE WITH PTERIDOSPERMALE

1. Abnormal occurrence of microsporangia and ovules of ginkgo on the leaves. 2. Presence of collar at the base of the ovule in ginkgo is compared to the cupule of pteridospermous ovule. 3. Presence of leaf gap in the stem. 4. Wedge shaped leaf with dichotomous venation can be compared with wedge shaped pinnules of some pteridosperms. 5. Seed of ginkgo resembles some pteriodsperm in size, presence of a distinct pollen chamber and in the nature of massive fleshy lyer.

C. RESEMBLANCE WITH CYCADALES:- 1. Dioeceous plant 2. Pollen tube haustorial in nature. 3. Spermatozoid are large and multiflagellate. 4. Presence of pollen chamber and a distinct nucellar beak. 5. Female gametophyte is large and massive. 6. Large egg and the ventre of the archegonia. 7. Longer period of free nuclear division in the proembryo 8. Endoscopic embryo. 9. Dicotyledonous embryo. 10. Hypogeal germination and the cotyledons remain embedded between the endosperm tissue. 11. Thick and massive integument of the seed and the persistent outer fleshy layer.

DIFFERENCES:- There is little difference regarding the origin of the leaf trace. In the cordaitals the two trace originates from same protoxylem group, where as in the ginkgo they originate from separate group of protoxylem.

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WITH BENNETTITALES: - 1. Similar embryo development. 2. Willium sonia is dioceous like ginkgo. 3. Presence of pollen chamber and nucellar beak. 4. Dicotyladenous embryo.

WITH OTHER FOSSIL GINKGOALES, BAIERA, GINKGOITES ETC. 1. Leaf resemble the modern ginkgo in shape and venation. 2. Male inflorescenece of baiera and ginkgo is similar in gross structure.

(a) Same line of dehiscence. (b) Distinct lump etc.

Some morphologist are of the view that the terminal ridge of the sporangiophore is an abortive microsporangium and subscribes to the view that the sporangiophore of ginkgo is derived by way of reduction from the sporangiophore of some fossil genera that had microsoprangia. E.g:- baiera

Presence of sunken stomats being surrounded by 4-7 subidiary cell that or a circle around it and have characteristics finger like projection overarching the guard cell in both the cases. In addition to these, the fossil member resemble modern ginkgo in both simple and complex features.

Conclusion: Thus after going through the detailed account of life history of G. bilaba is justified to call Ginkgo as living fossil as we have analysed their character on following bases:

1. Expcept ginkgo all the member of their order which flourished in Jurassic and Triassic of Mesozoic are now in fossil 2. Ginkgo has vegetative and anatomical characteristics that are purely coniferophytic but in many reproductive features it resemble to modern cycads, it also resembles the extinct

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cordiatales and even cycadeoides (delevoryas, 1971) in some features. This synthesis of characteristics from various extant and extinct groups in one living plant certainly makes it a treasure for the botanists and hence it has rightly been considered a living fossi.

It as a living fossil.

(b) EPHEDRALES

Order Ephedrales includes a monotypic family ephedraceae , consisting the taxon Ephedra. It is one of the highly evolved group of gymnosperms. The plants are mostly small or perennial herbs or shrubs. They usually grow in xerophytic habitats. The leaves are minute and scaly. Resin canals are absent and the medullary rays are multiseriate. The plants are dioecious and bear compound strobili.

CLASSIFICATION: CONIFEROPHYTA CONIFEROPHYTA EPHEDRALES GNETALES EPHADRACEAE EPHEDRACEAE EPHEDRA EPHEDRA A/C EAMES 1952 A/C SPORNE 1965

The family Ephidraceae includes single genus called EPHEDRA. It is represented by foUR species. Plants are mostly xerophytic shrubs or woody climber and lianes. The species reported in India are as follows:

i) E.foliata: It is a scrambling shrub, attain heigh of 6 meters. ii) E.gerardiana: It is a perennial herb. iii) E. Intermedia iv) E. Nehrodensis v) E.regeliana vi) E.sexatilis

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

DISTRIBUTION:

Ephedra is widespread and sporadic in distributionin and regions of tropics and sub tropics of northern southern hemisphere. E.foliata found in the drier parts of Rajesthan, Punjab & Haryana. E.gerardiana grows in Baluchistan . it is also found in panji, lahaul and spiti valleys.

EXTERNAL FEATURES: - 1. The stem is green, hard, ribbed, glabrous and much branched, stem is distinctly joined, slender and has long internodes. The branches are also green and photosynthetic. 2. The leaves are deciduous, opposite or whorled, more or less connate basally and usually reduced to membranous sheaths. Each leaf is inervated by two unbranched veins that run parallel to each other. The scale leaves bear a bud each in their axils. 3. The plants are usually diocious and only rarely monoecious. Fames regards the monoecious condition as an abnormal state of development and calls such plants as monstrosities.

REPRODUCTION:-

All the species of ephedra are dioceous and bear male and female reproduction organ on different plant. These plant do not shows any different in their vegetative organisation and can be recognized only when reproductive structures appears.

MALE STROBILUS:-

The microsporangiate strobilus of ephedra is regarded as a compound structures. These strobili arise in clusters from the nodes of branches. Each strobilus arise in the axil of a scale leaf. Each strobilus consists of a central axis that bears two to eight pair of

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decussately arranged simple broad and cupped bracts. The basal one or two pairs of these bracts are sterile, whereas the upper ones bear each a solitar-y male shoot or microsporangiophore and bears terminally 8-12 microsporangia that are sessile and dehisce terminally. These fused basal bracts are also called bracteales or perianth part. The male flower is also called a simple strobilus. There are slight variation regarding the number of male flower or simple strobili arising in the axil of each of the compound strobilus.

In E.gerardiana and E.foliata one simple strobilus arises in the axil of a bract. According to Eames 1952 the male shoot is single,bears two fused bracteolus and two sporangiophores become antagonically fused ( external sign of fusion ) . in E.antisyphilitiath single sporangiophore shows no external sign of fusion. In E.intermedia and E.distachya two or more sporangiophores arise separately in the axil of the two fused bracteoles.

MICROSPORANGIUM:-

The sporangiophores arises as small protrubences in the axil of the fertile bract of the bract of the male strobilus. The two perianth lobes arise laterally from the base of the protruberance. The apex of sporangiophore becomes lobed after growing for sometimes. Each lobe represents a sporangium. A hypodermal group of

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

archesporial cells becomes apparent in each lobe and consists of large cell with distinct nuclei and denser contents. After a little period of growth each archesporial group of cell in each sporangium becomes divided into two group by the appearance of a band of sterile cells ( singh & maheshwari, 1962). This indicates that a singles sporangium becomes two chambered. Now each group of archesporial cells divided by periclinal wall to form a outer layer and an inner layer of primary sporo nous cells. The primary sporangeous layer undergoes two periclinal divisions to forms a middle wall layer and an inner tapetal layers. The sporangeous call undergo division in all planes to form a group of sporogenous cell that divide further to form a large number of microspore mother cells. During these stage of development, the middle wall layer becomes crushed. The microspore mother cells divide meiotically to form tetrahedral tetrads of haploid microspores.

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MEGASPORANGIATE STROBILUS OR FEMALE CONE:-

Female cone usually arise in pairs at each node, in the axil of scale leaves. Sometimes three or four strobili may be at each node.. Rarely a single stobilus may terminate at the main aix ( singh and maheswari, 1962). A female cone appears to be an elliptical structures with a pointed apex. It is a compound strobilar organization and consists of a short axis to which 3 or 4 pairs of decussate bracts. The lower bracts are sterile whereas the upper two bear an ovule in their axils. Each ovule terminates a short stalk. The stalk and the terminal ovule are also termed as a female flower.

MEGASPORANGIUM:- A young ovule has a nucellus made up of parenchymatous cells that shows a hypodermal archesporial cell. The nucellus is surrounded by two layered envelope i.e outer and inner integuments. The inner integuamwnt grows at its tip into a long cylindrical tube ( micropylar

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

tube ). The inner integument is fused with the nucellus at its base and a little distance above but is quite free above. The archesporial cell divide periclinally to cut off several outer cells and an inner cells. The former constitutes the parietal cells, whereas later is called the megaspore mother cell. The megaspore mother cell undergoes meiosis to form a linear tetrad of haploid megaspores. Usually the lowest or the chalaza megaspore is functional and developed into a cellular female gametophyte.

GAMETOPHYTES The male and the female gametophytes developed from the microspores and the megaspores, respectively . the spores are, therefore, the pioneer structures of the gametophyte generation.

MICROSPORE, AND THE MICROGAMETOPHYTE:-

The microspores start germinating in the microsporangium. The microspore nucleus divided to form a small lenticular male prothallus cells and a larger cell. The nucleus of latter divided again to form a second male prothallus cell marked off from the large antheridial cell by a cleavage of cytoplasm. The two male prothallus cells start degeneration. The nucleus of the antheridial cell divides into a small generative cell and a tube cell. The generative cell divides by a perclinal walls into a stalk cell and a body cell. At this 5- celled stage the semierminated microspores are released through an apical slit in the microsporangium and are carried by wind to the microphyles of ovule. Development of the pollen tube and formation of two unequal male gemetes by the division of the body nucleus.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

FEMALE GAMETOPHYTE:-

The chalazal megaspore is usually functional. It enlarged and its nucleus divides into two. These nuclei move toward the opposite poles and are separated by a large central vacuole. Later 4,8 and 16 free nuclei are formed. These are arranged in a peripheral layer around the central vacuole. Later the central vacuole disappears and the free nuclei, are evenly disturbed throughout. In E.foliataand

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

E.gerardianathe mature gametophyte is almost obovate with a board micropylar and a pointed or tapering chalezal end. Wall formation iscentripetal and makes the female gametophyte a cellular tissue with a broad micropylar end and a narrow chalazal end archegonia developin the micropylar region where as the chalazal region acts as the food storage zone. In E.trifurcaone or two archegonia develop, where as in E.foliatathere are three and in E.gerardianathe the number may be 3 or 4.

ARCHEGONIA:- The archegonia developed from superficial cells called archegonial initial. Each archegonial initial divides by a transverse wall to from an outer primary neck cell or neck initial and an inner central cell. The neck cell undergoes a number of division to form a long and massive neck of about thirty to forty cells. The neck of archegonium is ephedra is the longest in the gymnosperm. The central cell enlarges in size and assume an elliptical appearance with pointed or

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

narrow chalazal end. Its nucleus divideds into aventral canal nucleus and an egg nucleus. The egg nucleus moves to the centre of the archegonium. The ventural canal nucleus degenerates. The central cell surrounded by a distinct jacket layer. FERTILIZATION:- The pollen tube along with its four nucleus grows through the archegonial neck and discharges into contents into the cytoplasm of the egg. Its tip swells and burst. The larger male nucleus migrates toward the female nucleus. The female nucleus is surrounded by a dense cytoplasmic sheath The male nucleus moves through this sheath and fuses with the female nucleus. The fusion nucleus along with its surrounding cytoplasm is termed as oospore or the zygote.

SEED:-

After fertilization, the ovule is transformed into seed. The mature seed is ovoid to triangular and consists of a large embryo embedded in the female gametophytic tissue and a membranous nucellar layer surrounded by a hard seed coat. As the seed matures, the adjacent bracts of the female strobilus developed into a thick and fleshly layer which formed an additional integument to the seed.

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(c.) GENETALES

The order gnetales comprises three very different but apparently related gebera of extent. seed plants with uncertain affinities. These genera are ephedra, gnetum, and welwitschia. Based on their generals morphological and habitates, one would hardly guess that the plant making uo this disparate group are related. Many studies supported by cladistics analysis indicates that three genera are indeed related. The order gnetales are considered to be the highest evolved among gymnosperm and are believed to show an approach to the angiosperm. These characteristics are vessel in the wood; compound strobili made up of small flowerlike unit with either a perianth and a whorl of more or less fused microphylls or a terminal ovule surrounded by one or more additional envelopes; reduction of the megagametophyte ( norchegonia ) and cellular embrogeng in wilwitschia and gnetum; dicotyledon like leaves in gnatum. Based on these and other similarities , such as siphonogamy and leaves with several ordered of reticulate venation. Many author have suggested that some kind of relationship exists between the genetales and the angiosperm ( dayle and donoghur, 1986; crane 1988; friis and endress, 1990). Its most of the characteristics have attracted the attention of botanists to considered it as progenitor of angiosperm’’.

DISTRIBUTION SEPARATED NY GENUS:-

Green – welwitschia Blue – gnetuma Red – ephedra Purple – gnetum and ephedrae

Through it is clearly they closely related, the exact evolutionary inter relayionships between gametophytes are unclear. Some classification hold that all three genera should be placed in a single order gnetales.

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While other classification say that should be disturbed among three separated orders, each containing a single family & genus. Must morphological and molecules studies confirm that the gener gnetum and welwitschia diverged from each other more recently than from ephedra ( arber and parkin 1908 ) ( peter crane marie frills 2004 ), ( bowe, coat and pamphill 2000).

CLASSIFICATION OF GNETALES:- Sporne ( 1965 ) divide genetals into following three unigeneric families

I) Gneteceae : gnetum II) Ephedraceae : ephedra III) Welwitschiaceae : welwitschia

GNETUM:- The plant body is sporophytic and resembles remarkably with a dicotyledonous plant, specially when it is not in the fruiting stage. Most of the species are lines or climber with twining stem, expect a few which are shrubs or trees, e.g G.greman and G.custatum

Welwitschia: w.bainesei (w.mirabilus) is the only species of genus welwitschia. The sole representative of family welwitschia of Gnetales . this is the most strange or bizarre of all gnetalean plants showing a very restricted distribution in a narrow coated belt of about 1000km long in South- west Africa. The specific name (W.mirabilis) of this African genus is very appropriate because the adult sporophyte is unkike that of any known planet on the earth’’. According to the recent nomenclature changes, however, the correct and valid name is w.bainosii. the common name desert octopus is often riven to this genus because of its peculiar habitat.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

Ephedra: The lone genus of family Ephedraceae of order Gnetales, is represented by some 40 species. It is distributed in mountanour or rocky place or in sandy desert regions throughout the world. Most of the species are shrubs and a few are lianes. E.triandra, a south American species, usually reaches upto diameter of 30cm and a height of several meters and appears like a tree . khushoo (1961) states that haploid chromosome In Ephedra is 7 and 14. Ephedrine a well known drus Is obtained from its various species.

Gnetum: MORPHOLOGY: Gnetum plants are shrubs, tree, or climbers with twining stems and in general habit resembles a dicotyledonous plant. The main hestem bears two types of brances a short shoot of limited growth and a long shoot of unlimited growth (internodes absent). The leaves crowded in one plane, in dicussats pairs, so that the branch look like a pinnate leaf. The lamina is large, oval,entire with reticulate venation and gives a typically docotyledonous appearance.

ANATOMY: ROOT:- The root is diarch. The cortex comprises several layers of large polygonal cells filled with starch grain and numerous thick walled fibres. An endodermis and 5 or 6 layered pericycle are present. The sec.growth is normal; the redial bars fo sanio. The xylem element in the root are larger than those of them contain starch grain in later stages. The phloem consists of thin walled broad rays packed with starch grain, which makes the wood of the root comparatively soft and again of the stem.

STEM:- There is a distinct tunica corpus organization. The cell at he apex are larger and vacuolated than those in the flakes. Periclinal division occurs in the tunica during initiation of the foliar buttress. The corpus comprises two or three layers of sub apical initial , central mother cell zone, flanking layers and pith rib merisrem . the wood consists of tracheids and few veseels and the phloem comprises sieve

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cell and phloem parenchyma. The pith is parenchyamatous when ypung;later the cell toward the vascular ring becomes thick walled , lingnified and have numerous pits.

The xylem consists of highly tapering tracheids, vessel and paranchyam . the latter are round or elongated with simple pits. Vessel structures was studies by mohmmed and sattler ( 1982 ) in G.montanum by light microscopy, SEM and TEM. Both primary and secondary xylem have vessels. Each vessel has two usually similar , perforendon plates at the two ends. The perforation may be scalaroid, scalariform perforation in alternate rows – commonly in the nodal region of stem (fig).the simple perforation plate is more common in the late metaxylem, especially in the secondary xylem. Crlquist(1994,1996) and carlquist and robinson (1995) do not agree that perforation plates in gnetum are scalariform or scalariform like.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants

LEAF:- A vertical section of a leaf shows a well marked cuticle on epidermal cells with undulate wall on both surfaces and the mesophyll of single layer of short palisade cells and a wall developed spongy tissue. The ...... are arranged in a curved . The xylem phloem cells are arranged in regular rows. In G.ula, takeda (1913) reported syndotocheilic development of stomata in the leaves of gnetum. However , P.MAHESHWARI and V.VASIL (1961) reported haplocheilic development in G.ula and G.gnemon. FIG

REPRODUCTION:- The male and female strobili consist of a stout axis which bears a basal pairsof opposite and connate bracts and usually six to eight superposedcupulus or collars. The cupules arise as annular protrubences in acropetal succession ( takcso and bouman, 1986 ) and an annular rim is formed at the axillary position of each cupule.

MALE STROBILUS:- There to six rings of male flowers developed basipetally above each collar (fig). A single ring of abortive ovules may occure above the flowers. The flowers in the different ring are arranged alternately. A male flower consists of a stalk bearing anthers enclosed in a perianth.

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MICROSPORANGIUM:- In a young anther, the hypodermal archesporidal cell divide and gives rise to a multicelled archesporangiumthe outermost layer divides periclinally and differentiate into the parietal and sporogenous cells. The formers divides again to produced on outer wall layer and the tapetum (fih). The narrow tangentially elongated wall layer cells becomes compressed during of the microspores mother cells. During dehiscence the epidermal cell becomes radially enlarged and the outer wall becomes slightly thickened and cutinized. From the inner tangential wall , fibres bands of thickening run upward and outward to the outer wall of each cell. The anther opens along a row of similar cells, which extended vertically on either side from the tip to some distance below the another sac.

MICROSPOROGENESIS:- The sporogenesis cells undergo further division and the microspore mother cells contain dense cytoplasm and prominent nuclei. Prior to meiosis the protoplasts receds and a special mucilaginous wall is secreted between the protoplast and the mother wall. The reduction division are simulataneous and cytokinesis takes place by centripetal furrows. The tetrad are tetrahedral, isolateral and decussate. As the microspores enlarged , the cellulose wall is gradually absorbed , the original wall breaks down and the young microspores are released . according to gulvag (1966), the pollen grains of G.ula G.gnemon have a single layer of lamelled exine.

MALE GAMETOPHYTE:- The mature pollen grain is shed at the three celled stage ( mahesgwari and V.vasil 1961, mastens 1971). The division of the microscope nucleus result in a small lenticular and a large cell ( fig 20.13 A-C). The lenticular cell rounds up, does not divide further nor take part in the development of the pollen tube and degeneration. The nucleus of the larger cell divide again and of the two nuclei, one hyaline with a large nucleous and is the first to enter the pollen tube. The second nucleus

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is rich in chromatin has cytoplasm sheath of its own and divide in the pollen tube to gives rise to two male gametes.

FEMALE STROBILUS:- A female strobilus usually has 6-8 collars and a single ring of ovules above each other. Two to eight ovular primodia differentiate from the annualar rim. The latter becomes conspienous before initiation of the ovules. Gradually the ovule becomes visible in the upper edge of the each collar. The upper few collars have no ovules.

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OVULES:- The cells in the epidermal and sub epidermal layers of the ovular primordium divide actively. The dermal cell undergo both periclinal and anticlinal region, which bears ovule and a lower cushion like area. Three envelopes arise acropetally on ovular primordial and enclosed the nucellus. The outer envelopeis the first to differentiate . It arises laterally to the ovular pridermal cells. About 30 vascular strands are present at the level just above the junction between the inner enveloped and the nucellus. The inner enveloped arises last . it developed as a tubular wall around the newly outlined nucellus , grows rapidly and form several lobes at the apex. It forms a micropylar tube which extened beyond the rim of the two outer envelopes. Soon after pollination the apical part breaks off. A few cells of the hypodermal layer of the nucellus divide periclinally to form the parietal tissue and sporogenous cells. The sporogenous cell divide further and produced nearly 12 megaspore mother cells. A nucellar cap is formed by periclinal division of the apical dermal layer. During the development of the nucllus, a few megaspore mother calls degenerate. While there cells are preparing for meiosis I,a fan shaped tissue of radiating rows of nucellar cells appears at the base of female gametophyte.

MEGASPOROGENESIS:- Meiosis is non synchromous in the developing megaspore mother cells. Walls are not laid down after meiosis i and ii, which results in the formation of a teters nucleated wenomegaspore (fig 20.18 A-D). The four nuclei later move to the peripheral cytoplasm surrounding a central vacuole.

FEMALE GAMETOPHYTE:- A number of coenomegaspores developed simultaneously , but only two or three reach the 16-nucleat stage. The nuclei undergo repeated division which are synchronous in the beginning. Mitosis proceed in a wave from the base upward , and different divisional stages can be seen in one end the same female gametophyte. In G.ula and

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G.Gnemon, the division are intranuclear , the nuclear membrane disappears at the anaphase. Free nuclear division continue till a definite number of nuclei have been produced, which varies in different species. As division continue, the gametophyte takes to from of an inverted flask. The upper part is wide and contain the vecule and in the narrow lower part the nuclei aggregate densely. The female gametophyte grows toward the chalazal end. simultaneously at fertilization or immediately after

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POLLINATION:- In G.ula and G. Gnemon, a drop of sugary fluid exudes from the tip of the micropylar tube and catches pollen grains. The slimy pollination drop has appreciable quantities of reducing sugar in G. Gnemon (piji 1953). Surface evaporation causes the contraction of the column of fluid, which brings about the withdrawal of pollen grains down to the nucleus. Anemophily is probably concerned in the transfer of pollen to the female cone, though entomophily may also be involved.

BOTANY PG SEMESTER – II, PAPER –V BOT521: Taxonomy and Diversity of seed plants