Subject BOTANY Paper No V Paper Code BOT521 Topic Taxonomy and Diversity of Seed Plant: Gymnosperms & 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 plants 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 Gymnosperm as a group distinct from angiosperm due to the presence of naked ovules. 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 genus giankgo. Van Tieghem (1898) treated Gymnosperm as one of the two subdivision of spermatophyte. To accommodate the fossil members three more classes- Pteridospermae, Cordaitales, and Bennettitales 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) Ginkgoales 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) Caytoniales 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. Lyginopteridales 2. Medullosales 3. Callistophytales 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.) PENTOXYLALES (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 ferns which have advanced to a semiangiospermic level of development from the Jurassic 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 leaves, 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 pollen 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 (leaf 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 tree. In no cases they were as thick as cycads 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 Glossopteris. 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 fruit 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 seeds. 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