The Palaeobotanist, 31 (I): 82-99, J983.

ELEVENTH BIRBAL SAHNI MEMORIAL LECTURE STATUS AND POSITION OF

R. S. CHOPRA (Retd) Reader, Botany Department, Punjab University, Chandigarh J60 015, India

INCE 1879, when Leitgeb pointed out Al£AE BA'!nPHYlJ\ PTEAIDOPHYTA some anomalies in hornworts (or antho­ Scerotes), a small natural group of , their status and position have been a subject of lively discussion. Fulford (1965, p. 3) wrote, "The Antho­ cerotales or Anthocerotae if you will, ~ is a taxon with very many gametophyte ~ ~ and characters unique to itself. z ~ Whether it is very closely or more distantly , related to other Hepaticae remains to be proved" . OOGAMQUS , ". AAS~£GONIATE Campbell (1895) derived pteridophytes from anthocerotes. Later (1925, 1940) he TEXT-FIG. 2 - Relationships (ideas of Bower, derived the Psilophytales from the Antho­ Goebel & Steere). cerotaJes (Text-fig. I) which in turn were derived from the Chlorophyceae. algal oflgln of bryophytes, or that they present an evol utionary way station between algae and higher , and concluded that PTERIDOPHY!.\ thE yare an offshoot of the Archegoniatae, a "dead end". An adaptation of the MARCHANTlALES phylogenetic scheme by Zimmumann (1932) MUSCI expresses these relationships better (Text­ \ .OBf\YALE'S fig. 3).

ALGAE BRYOPHY"IAPTERIDOPHYTA

PSILOPHYTALES

BRYOPHYTA

ANTHOCEROTALES CHLOROPHYCEAE

TEXT-FIG. 1 - Phylogeny (after Campbell, 1940).

Goebel (1898, 1905) refuted Campbell and considered the Bryophyta and the Pterido­ Green chyta as tWo independent lines. Later (1930) Auto,troPhs he concluded that the Bryophyta are not ,: • connected with any taxon either upwards or downwards. Bower (1935) supported Goebel TEXT-FIG. 3 - Phylogeny (adapted from Zimmer­ (Text-fig. 2). Steere (1969) rejected a direct mann, 1932). Present address: 2132 - J5C, Chandigarh J60015, India. 82 CHOPRA - STATUS AND POSITION OF HORN WORTS 83

To decide as to the ideas of which school DATA AND DISCUSSION of thought are more tenable than those of the other and to incorporate the comments HAPLOPHASE of various authors, where necessary, it is desirable to cover the entire gamut, con­ The habit of growth, but for the presence sidering and evaluating all features, rather of colonies of Nostoc in the thallus, re­ than dwell upon a limited number offeatures sembles that of the thalloid MetzgeriaIes. (cf Howe, 1898: peculiar chloroplasts, Cavers (1911, pp. 90, 91) wrote, "The sunken sexual organs, meristematic seta, mode of apical growth is of interest and sterile columella and stomata on the capsule even of value in helping to understand the wall). morphology of the body with special

A B c

o F --~.,P.

H J K

TEXT-FIG. 4 - Showing sections of apical cell and divisions in segments. A, B, diagramatic transverse and longitudinal sections respectively. Haplomilrium gibbsioe (after Campbell)- C, D, transverse sections of Porella and P/agiochila respectively; E, a segment of either C or D; F, transverse section; G, a segment. Pelalophy//um - H, transverse section; I, a segment.. Fossombronia- K, a segment. Mefzgeria. Abbreviat­ Ions -CoP, cortex slem primordial;. LP, leaf pfimordJal; McP, mucilage pfimordJum; SP, stem primordium; LaP, lamella primordium; MrP, mldflb pfimordJum: 84 THE PALAEOBOTANIST

c

F , , . VI 11 G 5 v~ 03

TEXT-FlG. 5 - Vertical longitudinal sections- A, Dendl'ocel'os: B, Anlhocel'os (schematic afler leitgeb); C, Notothylas bl'euleii, x 600 (after Campbell); D, Anthocel'os (Phaeocel'os), x 390 (afler Bharadwaj); E, Pellia epiphylla, x 450; F, Pallavicinius cylindl'icus, x 225 (both after Campbell); G, Riccio glauco, X 325 (after Smith). The numerals indicate the position of apical cell, while 0 and V stand for dorsal segments. The cells between two epidermis in fig. C are dotted.

reference to the origin of the differentiation Marchantiales, follows more or less the same into stem and leaves n. ThJs is an apt pattern. description with regard to the Calobryales, In Calobryales (Text-fig. 6) a cortical Jungermanniales and such Metzgeriales as cell is transformed into an apical cell of a they have two- or three-sided apical cells. branch. Several types of branching have Different types (Text-fig. 4) are: Calobryales, been recognized in the Jungermanniales. Jungermann~ales,Petalophyllum - Fossom­ However, for our limited comparison (Text­ bronia and Metzgeria. fig. 6) we may note intercalary and apical . In taxa where the apical cell, as a rule, branching. Jn the former case a branch cuts off four sets of segments (Text-fig. 5) arises endogenously on the lower side of the development of the plant body, subject to stem and in the latter case a branch pri­ the interpolation of air-chambers in the mordium is developed in one cell either CHOPRA - STATUS AND POSITION OF HORNWOlnS 85

•I

A E

TEXT-FIG. 6 - Branching. A, vertical section of part of a stem of HaplomilriunT, x 175 (after CampbelJ); B, origin (diagrammalic) of a branch primordium in a member of the Jungermanniales; C, horizontallongi­ tUdinal section of Melzgeria !llrcoLa, X 540 (after Strassburger through Goebel); D, horizontal longitudinal sections of Anl/wceros (after Goebel); E. horizontal longitudinal section of Riccia glauca (after Campbell). Abbrevialions - mh, mucilage hairs; m' m', first and second grade marginal ceIJs; ML, middle lobe; p, surface cell of the first grade; t' t', old and new apIcal cells. of a leaf or an amphigastrium primordium. Bower (1935, p. 10) wrote, "A peculiar In the Metzgeriales, where there is always a structural feature, of occasional but not single apical cell, ventral branching is exo­ constant occurrence, is the presence of genous and branching in the horizontal stomata-like clefts on the lower side of the plane of the thallus is pseudodichotomous thallus" (Text-fig. 7). Leitgeb (1879) gave the and similar branching in Sphaerocarpus, same name to both these structures (Spalt­ Monoelea; in Marchantiales and the Antho­ bffung). Goebel (1930) considered these cerotales where there is a single apical cell clefts to be homologous with the stomata or a group of such cells, is truely dicho­ (Text-fig. 8). Mucilage slits (Text-fig. 7E) tomous and is accompanied by the develop­ have been recorded on the upper surface ment of ' middle lobe '. of the thallus. Bower (1935, p. 23) after If diverse types like the Calobryales, due consideration concluded, "A picture Jungermanniales, Metzgeriales with three- or would thus be suggested of the original two-sided apical cells, and those with four­ haplophase of the Anthocerotales as a fully sided apical cells, Sphaeroearpus, Monoclea equipped photosynthetic structure, probably and the Marchantiales (subject to interpola­ terete like the present diplophase ". It is of tion of air-chambers) can be retained in interest to note the presence of stomata one taxon by those who segregate the on the gametophyte of Rhynia gwynne­ Anthocerotales from the Hepaticae, why vaughani (ef Pant, 1962). shou Id the anthocerotes alone be segre­ Proskauer (1960) writi ng on his" common gated? ancestral denominator" speculated the pre- 86 THE PALAEOBOTANIST sence of stomata in this hypothetical taxon. Campbell (1940) have rightly placed the It is conceivable that the early archegoniates anthocerotes in a position preceding other had stomata on both phases. In the later taxa. taxa, this expression was governed by eco­ Cavers (191 1, p. 141) wrote, " In every cell logical or habit of growth considerations. there is, in most species of Anthoceros a In Cythodium (Lang, 1905; Kashyap, 1929) single large chloroplast, with a conspicuous pores are present on the lower side of the pyrenoid" and on p. 143 he wrote on the thallus in small plants (those on the upper chloroplasts in the capsule waH, " each cell side are seen only in large plants) as an contains two chloroplasts". A part of this adaptation - not to reduce photosynthetic concept is considered here and part will be surface in small plants, growing in reduced taken up with the sporogonium. Campbell light. (1905) had expressed the same view in Regression of the mucilage clefts and respect of the haplophase chloroplasts and stomata (to be taken up later) has made a noted the presence of two chloroplasts in a beginning in this taxon, i.e. a trend towards species of Anthoceros. Again (1925, 1940) their total elimination, a feature charac­ he compared the Anthocerotales with the teristic of other liverworts, has set in. Ulotrichales. In the later year he noted Combination of this primitive feature that: A. pearsoni has two chloroplasts, with the advanced features of the Marchan­ A. howelli has four and as many tiales (shape of the apical cell, development as twelve in the inner cells of the thallus. of the thallus and branching in the hori­ A species of Dendroceros (Text-fig. 7) has zontal plane of the thallus) suggests that the on the lower side of the thallus a single anthocerotes, in their evolutionary march, large chloroplast in each cell of the epi­ have travelled longer than any other cor­ dermis; but two or three chloroplasts in responding group of liverworts. Kashyap each guard cell. A. husnotii, A. puncfatus (J 929), Goebel (1930), Bower (1935) and and Megaceros have no pyrenoids. Further

c A B ;fit @ F o E

TEXT-FlO. 7 - Mucilage clefts on the thallus (all after Goebel). A, Dendroceros sp. (epidermal cells have one chloroplast, guard cells have. two or three chloroplasts each); B, Anthoceros sp.; C, Anlhoceros; D, Anthoceros sp.,- a st.oma wIlh a divided guard cell; E, Megaceros wlh a cleft (from the upper surface); F, Anlhoceros, a cleft Without openlog. CHoPRA - STATUS ANn POsITION OF l-IORNWO.lUS 87

the Marchantiales. This is foUowed by periclinal walls in each of the four cells to produce primary wall and primary andro­ gonial cells. 'I~~In the Anthocerotales the initial divides \1A 0 C 0 E transversely into an outer and an inner cell. The outer produces two-cell thick TEXT-FJG. 8 - Stomata on the capsule wall. A, roof of the antheridial chamber. The inner Anthoceros; B, Dendroceros crispil/lls (rudimentary); cell produces either one or more antheridia C, Megaceros (functional); D, Megaceros (rudimen­ in each chamber. In either case the body tary); E, Megaceros stoma-mother cell with oblique of the antheridium develops as in Sphano­ division. carpales and the Marchantiales. In Mara/lia the flush initial, as in Antho­ ceros, divides in the same manner. The outer cell produces the roof of the antheri­ studies are likely to add to these examples dial chamber. Here ends the resemblance of more than one chloroplast per cell of the with Anthoceros. The inner cell develops haplophase. This feature is not universal into spermatogenous tissue, without a stalk either in the anthocerotes or in the green and antheridial wall, in the antheridial algae. chamber. Bower (1935, p. 23) wrote, "The Antho­ Campbell (1925) noted a developmental cerotales show in this detail of chloroplast­ similaritv between the anthcridium of number a scale of variation towards the Notothylas and Marattia. He had done so state habitual in the higher plants, viz., in 1895 (see Goebel, ]905, pp. 185, 186). that with numerous smaJl chloroplasts". Goebel (1905) wrote, "The mature antheri­ This feature does not warrant the segregation dia are constructed like those of other of the Anthocerotales, nor their derivation Hepaticae with a wall-layer, stalk, and other from the green algae, because this resem­ parts, and its cellular construction is like blance cannot overrule the limitations what OCCurs elsewhere amongst Hepaticae, imposed by oogamous reproduction. but is known in none of the Pteridophyta 5. Oil-bodies have so far not been re­ ...... " The endogenelic origin corded in this taxon. is evidently a secondary phenomenon ... 6. Initials of the sexual organ in bryo­ ...... " When Campbell endeavours phytes other than the Anthocerotales become to find an analogy between the antheridium papiJlate and project above the general of Marattia and an embedded antheridium surface of the haplophase (Text-figs 9, 10). of Anthoceros, which is covered on the out­ Similar is the case in the antheridiu m initials side by a double ceJl-Iayer, and to do so in Leptosporangiate ferns. Sometimes (cl has to imagine the waJl-layer and the Bower, 1935, p. 510, fig. 397) the archegonia stalk to be absent, the comparison seems too are not sunken in this taxon. In the to me to be bred of the wish to discover AnthocerotaJes, Psilotales, Lycopodiales and points of relationship between the Bryo­ Eusporangiate ferns the initials are flush phyta and Pteridophyta, and not to be with the general surface of the haplophase. founded on facts". According to Bower (1935, p. 516) this is the The spermatozoids in anthocerotes are simplest method of protection of the arche­ bicilliate and according to Bower (1953, gonium and the young sporogonium. In p. 1I) they resemble those of other Hepa­ , except the secondary archegonia of ticae. In the Marattiaceae the spermato­ Sphagnum, these initials develop apical ceJls. zoids are multiciJliate. Howe (1898), Campbell (1905, 1925, 1940) Subject to minor details in the sequence and Mehra (1967, 1968) have over empha­ of waJls and Sunken nature in antho­ sized this feature to segregate the antho­ cerotes, the development of the archegonium cerotes from the Hepaticae. (except the Calobryales, see CampbeJl, 1920, The antheridium initial (Text-fig. 9) by CampbeJl, ]959) follows the pattern of transverse divisions produces Some discs, Riccio, i.e. an axial row of ceJls is cut off each of which undergoes two vertical inter­ by three peripheral or jacket cells, tram­ secting divisions in the Sphaerocarpales and verse walls make the archegonium double 88 THE PALAEOBOTANIST

t ~ c?:: .•: ~ ~l. %A fffj1 K

~. .::"...... ' F ~"""", 1J ® 4: B G L

c ~ W D

E J o

TEXT-FIG. 9 - Vertical sections showing antheridium development (diagrammatic). A-E, Spbaerocar­ pales (after Campbell); F-J, Anthocerotales (after Bharadwaj); K-O, Marattiaceae (after Campbell).

storied, another transverse wall cuts off take no fu rthe I' pa I't). The top cell under­ the cover cell and this cell takes no part in goes two intersecting vertical divisions. the development of the neck (Text-fig. 10). The four cells thus produced divide trans­ Campbell (1940, p. 60) wrote, "The axial versely to produce four rows of neck cells cells is next divided by a transverse wall (four rows of neck cells in Haplomitrium into an outer and an inner cell. From the are due to vertical division in one of the first by a similar division a terminal, or jacket cells instead of being laid in two or cap cell, is separated from the primary neck three jacket cells). The middle cell divides \ canal cell. The inner cell is later divided to produce the axial row of cells. into two l1'early equal cells - egg cell and Campbell (1925) compared the arche· venter canal cell. The primary neck canal gonium of Notolhylas with that of Marallia cell divides into four or five neck canal to indicate a close similarity, ignoring the "cells n. In spite of this difference the deve- differences in the development of the neck lopment remains hepatic. and neck canal cells in the two genera. In Ma/'attia the initial divides into two Bower (1935, p. 12) rightly ~'emarked, or three cells (the lowermost when three "The sexual organs of the Anthocerotales, CHOPRA- STATUS AND POSITION Of HORNWORTS 89

1J;I w K A ~ rJtr W;- L B

o" ~ 1$o c M

,~ o !N

I ~ ~ ~' J o E

TEXT-FIG. 10 - Vertical sections showing archegonium development (diagrammatic). A-E, Riccia glauca (after Campbell); F-I, AIII/wceros (after Bharadwa); J, showIng cap cells (after Campbell); K-O, Maraltiaceae (after Campbell).

though differing in certain details from derived type which at any rate shows no other Hepaticae, are clearly of the Hepatic­ near relationship to the Pteridcphyta. The type and this is so notwithstanding that kinship of Anthoceros to the Pteridophyta they alone are deeply sunk in the fleshy is then, so far as the sexual organs are thallus and that the antheridia are even concerned, a mistaken one". endogenous in origin". (Leitgeb, 1879; Foregoing comparison and opinions ex­ Lampa, 1903 noted exogenous antheri­ pressed do not warrant: dia). 1. Derivation of the Archegoniatae flom Goebel (1905, p. 186) on this topic wrote, ancestors like the modern green algae "in Anthoceros we have to deal with a with unicellular gametangia (Bold & Wyne, 90 THE PALAEOBOTANIST

1977), not even from Chara where growth or less spherical and the first wall, except of pericentral cells encloses the oogonium. the Anthocerotales and pteridophytes with 2. Derivation of psilophytes with pteridc­ quadripoJar embryo where it is vertical, is phytic archegonium (see Pant, 1962) from transverse. In most of the Anthocerotales anthocerotes with hepatic archegonium and (Text-fig. 11) the embryo is spindle-shaped vice versa. and the first wall is vertical. In mosses and pteridophytes with bipolar, exoscopic DIPLOPHASE embryo the hypobasal half forms the foot and the epibasal half develops an apical The zygote in the Archegoniatae, except cell. In no liverwort does an embryo most species of the Anthocerotales is more develop an apical cell and apical growth.

ffi1 8V1 'GJ8'EB'8 M /.1.\A, & G. r.t\ th .~.@'\1:J'~'Q7W 1 D Q D U

ll.©"~.,@;'.:~&:~. 13 0 'lJ .. GJ W \J7 1 D 1 CUI a

•' ~ ,III ".@:~EB-..@® "@-®-

~ ~~,~.J<~p .__ 9 .. <:, • • - oS • -- • & .•• '

~'.: ,Ef) :..j,@ '.:-::iJ

:~ ~@ '.:... ..:...... It::J,affi .. I'... Gl It II ~" ~.. .. .' ... 0 F L R TEXT-FIG. Il- Embryology of some anthocerotes (diagramatic) in longitudinal and transverse sections. A-F, Anrhoceros fusciformis (after Campbell); G-L, A. crispllius (after Bharadwaj); H-Q; A. erectlls (after Mehra & Handoo); R. Notorllylas orbicularis four-celled embryo (after Campbell). Roman figures indicate the sequence of walls. CHOPRA-STATUS AND POSITION OF HORNWORTS 91

Mehra and Handoo (1953) noted a 69) (Text-fig. 11A-E) shows this type of spherical zygote in An/hoceros cree/us development. (Text-fig. 11M-O). Transverse first wall Bhardwaj (1950, pp. 152-155, figs 19-23) has been recorded by Campbell (1905) in (Text-fig. 11F-L) described the embryology Notothylas orbicularis (Text-fig. 11R), of Anthoceros crispulus. Jn this species the Pande in N. indica, Bhardwaj (1950) in A. first wall in the zygote is transverse and not crispulus and Mehra and Handoo (1953) vertical. Octant development follows the in A. erectus. According to Bhardwaj same pattern as in the Marchantiales and (1958) Hofmeister found an oblique septum Anthoceros eree/us (Mehra & Handoo, in A. laevis. Leitgeb (1875) mentioned first 1953). Transverse walls are laid both in division in the hypobasal half to be vertical the hypobasal and epibasal halves to pro­ in Frullania dilata/a. duce a filament of four tiers of four cells Campbell (1940, p. 267) wrote, "There each. The lowermost two tiers, as in is a good deal of variation in the early A. fusciformis, develop into the foot, and development of the embryo in Equisetum the upper two tiers give rise to the seta arvense and E. maximum the basal wall is and the capsule as in A. ereetus and other transverse and this may be the case in species where the embryo consists of only E. debile; butin the latter case there is a three tiers of cells. Elimination of trans­ good deal of variation and the basal wall verse walls in the epibasal half too can may be vertical". The spindle-shaped zygote, result in an octant only. The embryo of and the first wall being vertical are derived A. crispulus in having, before periclinal conditions. walls are laid, four tiers of four cells each, The embryology of the Calobryales is resembles the filamentous embryo of the not sufficiently known. According to Calobryales, Jungermanniales, etc. Growth, Campbell (1959) the first transverse wall is following the laying down of periclinal not equatorial, the epibasal cell is larger of walls, makes it anthocerotalean embryo. the two cells. The second wall in each cell This embryology suggests how the octant is vertical. According to Campbell (1940) embryo of the Marchantiales may have the embryo comes to be of four tiers. Tn arisen. Tn mosses and pteridophytes the most of the Jungermanniales and the embryo has apical growth at least in the Metzgeriales, the hypobasal half produces epibasal half; while the Anthocerotaceae a haustorium and a filamentous embryo like other liverworts lack in apical growth. is developed from the epibasal half. The embryo is nearest to that of the Hepa­ However, in Frllllania dila/afa (Leitgeb, ticae. 1875; Cavers, 1911) and Fossombronia Foot tier is the first to become active and (Campbell, 1940) the hypobasal half pro­ grow into a foot to establish a close contact duces the foot. In these two taxa the with the thallus to draw nutrients from the embryo consists of three tiers of four cells latter. The top tier of four cells, cut off each, i.e. foot, seta and capsule tiers. bv the first transverse divisions in the Campbell (1940, p. 136) noted similarity epibasal half, differentiates into the' primary with the embryo of Anthoceros in this capsule' (where the seta adds to it from respect. below) or the capsule (where the seta does According to Campbell (1940, p. 39), not add to it). Former is the method of "In Anfhoceros, following the octant Anthocerotales and a few of the Junger­ division, a second transverse divisicn occurs manniales and latter is the method of rest and the embryo consists of three tiers, each of the Jungermanniales and the Metzgeriales, consisting of four equal cells (compare etc. Frullania and Fossombronia). The two Tn anthocerotes periclinal walls are laid lower tiers develop into the large foot. in the top or terminal four cells. This is The upper tier by further transverse divi­ followed by differentiation into: columella, sions, is separated into a terminal segment archesporium and the capsule wall. The in which the archesporium arises, and an seta tier becomes active and begins to add intermediate zone between this and the to the tissues of the primary capsule from foot". Thus at this stage the embryo is a below. filament of four tiers of four cells each. Cavers (1911, p. 119, fig. 82G, H, p. 120) Anthoceros fuseiformis (Campbell, 1905, fig. enlarged the observations by Leitgeb (1875) 92 THE PALAEOBOTANIST

on Frullania di/atata. Campbell (1940, pp. position. Many authors continue to follow 136-138) described this and some more him. cases where the seta does contribute to the Anthocerotes and sphagna are the only basal part of the capsule. He (p. ] 36) bryophytes where the entire endothecium found resemblance among F. di/alala, produces a sterile columella and the arche­ Fossombronia and SphaerocGlpus on one sporium arising from the inner layer of the hand and with Anthoceros on the other amphithecium is inverted over it. The (i.e. in all these cases the embryo consists condition in Horneophyton (see Bower, of three tiers of four cells each). In these ] 935, p. I20) is similar, though the columella cases the foot develops from the hypobasal is phloem part of the central stele. In all halffor close contact with the thallus. Other the three cases the archesporium is essen­ cases descri bed by him are: Lejeunea serpi­ tially axial in contrast with that of living folia, Radu/a and Cepha/ozia bidenlala. In pteridophytes, where it is hypodermal, or these cases the hypobasal half develops superficial in origin. In Sphagnum the into a haustorium and the whole sporo­ archesporium is enclosed in a spore-sac gonium is developed frem the epibasal half and a tapetum surrounds the sporogenous and the seta does add to the basal part of tissue in Horneophyton. the capsule. In RLidu/a (p. 137), "In the On the basis of a survey of the relative terminal segment the first periclinals define extent of the columella and the arche­ the primary archesporial cells, but similar sporium, various genera of anthocerotes divisions in the segments below the can be arranged in a series. At one end of apex also contribute to the archesporium, this series are types with a well developed which is much more extensive than in columella and a thin archesporium. The Fru//ania ". latter progressively becomes more massive Meristematic activitv of the seta in the and the former regresses. At the other Anthocerotales as compared with the end are non-columellate species of NoIO­ Jungermanniales and Metzgeriales is a Ihy/as. This genus is reduced and is no question of degree and not of kind. closer to other hepatics than is Anlhoceros. Cavers (1911, p. 149) rightly wrote, " meri­ In spite of the difference in the origin of stematic tissue above the haustorium of the archesporiuIT', it is nearer to that of the sporogonium of the Anthocerotales other hepactics than any other taxon evidently results from the persistence of a because of the absence of a spore-sac and a stage which is quickly passed through in tapetum. the development of the sporogonium in In the primitive taxa of hepatics other other Hepaticae ". than anthocerotes, spore-mother cells and Cam pbell (1925, p. 68) correctly ex pressed elater-mother cells belong to the same the fate of a normal sporogonium of the generation. As a result of sporogenesis Anthocerotales. However, as a result of there come to be four spores for each elater. his observations on Anthoceros ji/sciformis, In the higher taxa divisions are interpolated growing under exceptionally favourable between the original spore-mother cell and circumstances, he (p. 74) concluded that a the one that produces four spores. The close resemblance between this sporo­ result is presence of several spores to each gonium and the Devonian Rhyniaceae elater. warrants the assumption of a real relation­ In the anthocerotes converse is the case. ship between the latter and the Antho­ In Dendroceros, the most primitive genus, cerotaceae. He overlooked the fact that the elater mother cells do not divide (see this is the only archegoniate taxon with a Schuster, I966), and the ratio remains: four basal meristem in the sporogonium and the spores to one elater. In other genera the Rhyniaceae had apical growth. elater-mother cells divide mitotically; the Bower (1935, p. 109) rightly indicated cells generally rtmain united and the result that, "before basal intercalary growth alone is: four spores to one compound elater or no morphological future seems to be open". pseudo-elater. Often the pseudo-elaters Yet Campbell (1940) derived the psilo­ break, or undergo extra divisions, or some phytes or the Rhyniaceae from the Antho­ cells branch. cerotaceae (Text-fig. I). This had the effect In Dendroceros and Megaceros (where the of catapulating this taxon to an llnwarranted cens remain placed end to end) the elaters/ CHOPRA ~ STATUS AND POSITION OF HORNWORTS 93 pseudo-elaters develop spir.al thickenings, CYTOLOGY as in other hepatlcs. Hepatlcae IS the only taxon, where e]atersjpseudo-elaters are pre­ Mehra and Handoo (1953) on the basis sent, no other archegoniate has these. This of persi stent occurrence of m-chromosome in feature indicates that in spite of a difference Anthocerotales, Jungermanniale~,Sphaero­ in the origin of the archesporium, the carpales and Marchantiales suggested anthocerotes are nearer to Hepaticae than a monophyletic origin of these taxa. In to any other taxon. no pteridophyte do we find the presence Cavers (1911, p. ]43) and Bower (1935, of m-chromosome. p. ]5) ind icated that each cell of the capsule Proskauer (1960, p. 17) wrote, " I do not wall contai ns two large chloroplasts. wish at this stage, to go beyond my recent Campbell (1905, 1940) showed that each presentation (Pro~kauer,1958a) of the guard cell of stomata on the capsule wall cytological evidence suggesting the deriva­ of Anthoceros pearsonii has a single chloro­ tion of the typica I karyotype of Iiverworts plast. Bharadwaj (1965) note d that each from a kayrotype similar to that of typical cell in either phase of A. communis con­ hornworts. I do not concur with Tautno's tains a single chloroplast. Bower (1935, (1959) opinion on this point". Do these p. 16), on the authority of Schim­ features not conflict with the "An tho­ per, noted that most of the cells of rhyniaceae" concept? the sporogonium contain two chloro­ plasts, but those of the epidermis contain several chlorop]asts. A male gamete has no chloroplast, so doubling RELATIONS HlPS increase in the number chloroplasts or of The Anthocerotaceae are considered to in cells of the sporogonium is not due to be a synthetic taxon and conclusions that syngamy but due to fission - a condition are not warranted have been drawn on the that is normal in the Archegoniatae. It basis of these resemblances. It seems desir­ was the absence of this clear understanding able to discuss some of these relationships that lead some early authors to over before arriving at a conclusion. Those to emphasize a partial truth and suggest be evaluated are: (i) between anthocerotes a derivation of this taxon from green and other Hepaticae,(ii) between the Antho­ algae. cerotaceae and mosses through Sphagnum, Most species of Anthoceros and Phaeo­ (ii i) between anthocerotes and the Rhynia­ ceros (Text-fig. 8) are stomatose (A. halli ceae, and (iv) between the last taxon and has a few large stomata on the upper part mosses. of the capsule); some species of Folioceros To determine the relationship of the are stomatose; while others (F. fusciformis horn worts with rest of the Hepaticeae, and F. incurvans) are non-stomatose (,ee matter under data and discussion can be Bharadwaj, ]972); some species of Megaceros considered under three heads: (i) features have poorly developed or no stomata; that are hepatic, (ii) those that appear to species of Dendroceros either have regressed be different, but show a trend towards what stomata or none and Notolhylas in non­ is normal in other liverworts, and (iii) those stomatose. that are anthocerotalean, or nearly so. Proskauer (1948) indicated that a crosS Habit of growth, shape and segmentation section of Anl11Oceros capsule ~hcwsfour of the apical cell, further divi~ionsin the lines of dehiscence of which only two are segments or merophytes and development functional. This resembles the Calobryales of the plant body resemble those of the and Monocleales (with one of the lines Metzgeriales, Monoclea, Sphaerocarpus and being functional), the Jungermanniales and the Marchantiales; branching in the hori­ the Metzgeriales. However, according to zontal plane of the thallus agrees with the Proskauer (1948) the capsule does not last three taxa. Deve]opment and structure open by two valves in the beginning of the sexual orga ns are hepatic and not (cf. the Blyttiaceae). Openings appear pteridophytic. It is not fair to ignore these along two lines and they coalesce. features and over emphasize their sunken External agencies cause the opening by nature - the si mplest protecti ve device. two valves, But for the ;l bsence of oil bodies, the haplo- 94 THE PALAEOBOTANIST phase is hepatic. Absence of apical growth class from the Hepaticae, either Sphagnales recalls hepatic and Sphagnum sporogonia. should be considered a separate class apart Presence of a m-chromosome suggests from the Musci, thus making four primary lack of relationship with pteridophytes and divisions of Bryophyta or the Anthocero­ the karyotype is hepatic. tales and Sphagnales might be united to That the meristematic seta is the reten­ form a class". However, he retained the tion of a stage which is quickly passed customary two-fold division of the Bryo­ through in the Calobryales, Jungerman­ phyta. niales and the Metzgeriales is proved by Bower (1935, p. 65) wrote, "Sphagnum the embryology of Frul1ania di1atata, has always been ranked as a on Cepha10zia bidentala and Rudu1a. A single general grounds of ha bit. But now not large chloroplast per cell of the thallus only does the evidence from the sexual and two such chloroplasts per cell of the organs point to an intermediate position sporogonium concept is at best a partial between the mosses and liverworts, but statement and a single large chloroplast per also the primary segmentation and absence cell is not universal in green algae. of apical growth in the sporogonium and Increase in number of chloroplasts in the the amphithecial origin and complete dome­ cells of sporogonium is not due to syn­ shaped archesporium, are all features which gammy but due to fission - a condition point rather to the Anthocerotales than normal in the Archegoniatae. Elimination to the true Mosses". Campbell (1940, of mucilage clefts and stomata is a trend p. 185) wrote, "There are some significant towards what is normal in other liverworts. points of structure between Sphagnum and Absence of oil bodies and presence of a Anthoceros, indicating a possible remote tierd embryo (though longitudinal cleavage relationship" . disguise the underlying filamentous nature) Leaving aside ecological adaptations, and by comparison with mosses and pterido­ vegetative development and structure of phytes it is nearest to the filamentous type the haplophase of Sphagnum resemble those and is actually filamentous in Anthoceros of other mosses*. Sphagnum has no crispulus). Entire endothecium producing a elaters or pseudo-elaters, spores are en­ columella; the archesporium of amphithecial closed in a spore-sac, multistratose capsule origin inverted over the columella (remain­ wall lacks in intercellular spaces, the capsule ing essentially axial in contrast to the has an operculum and opens by an annulus. peripheral or superficial archesporium of Resemblances with mosses outweigh the pteridophytes); compound elaters in five differences between them, so the sphagna out of six genera (although the presence of cannot be separated from true mosses. elaters, and those of Dendroceros and Mega­ Besides the differences between the sporo­ ceros with spiral thickenings are features of gonia of Anthoceros and Sphagnum, the hepatics); and fully photosynthetic sporo­ gametophytes are so different that a close gonia, in combination, are features that are relationship between the two taxa is not not shared with any other group of liver­ warranted. Campbell (1940, p. 69) wrote, worts in combination. "It is possible, however, that the highly Bower (1935, p. 19) wrote, " The conclu­ specialized of the higher mosse sion from such considerations would be is a case of parallel development rather that the place of Anthocerotales is with the than an indication of any close relationships liverworts, but not closely with any section with Anthoceros." Bower (1908) and Chopra of them". The question does not remain, (1967) considered the Hepaticae and Musci whether the Anthocerotales are closely or to be diphyletic. Steere (1969) suggested more distantly related to other Hepaticae ? that the bryophytes are polyphyletic. It becomes, what are the status and position Presumably the Bryophyta are triphyletiE, of the Anthocerotales in the Hepaticophy- Takakiophytina constituting the third line. tina? • It may be of interest to note that all Cavers (19lJ, p. 196) on the relationship stages through which the extant fauna and between Sphagnales and the Antho­ cerotales wrote, " These two aberrant groups *Andreaea is unique in that the apical cell of the leaf does not cut off two sets of segments. show a striking resemblance to each other. A single segment is cut off by a wall parallel to tIl\; If Anthocerotales are to be made a separate posterior face of the apical cell. CHOPRA-STATUS AND POSITION OF HORNWORTS 95 flora have passed are not lost. Some of to be open". According to Proskauer them are retained either as fossils or in (1960) Kidston and Lang (1920) astutely some living taxa. A few examples of the forebore to consider the point of view that latter are: Takakia, in having parenchymat­ the psilophytes had an origin from Antho­ ous apices of the subterranean axes, and cerotes. genetically unfixed apical cells in aerial axes, Campbell (1925) ignored others' point represents a stage between the ancestors of view, made a comparison between the without apical cells (green autotrophs) and sexual organs of Notothylas and Marattia, those with them (Archegoniatae). Liver. noted a close similarity (though wrongly) worts, which have apical cells in the haplo­ between the sporogonium of Anthoceros phase but lack in them in the diplophase, and the sporangium of the Rhyniaceae and show an early stage in the evolution of concluded that a real relationship between the archegoniate diplophase. Anthocerotes, the two taxa is warranted. Goebel (1930), with peculiar chloroplasts, enable some Bower (1935) and Zimmermann (1952) did authors to connect this taxon with green not accept this point of view. algae. Basal meristem of Anthocerotales, Campbell (1940, p. 72) wrote, "The which has no morphological future open ancestors of vascular plants, if not actuaIly to it, is retention of a stage, which is quickly anthocerotes at any rate closely reHmbled passed through in other orders of the them". He (p. 190, fig. I) did not Hepaticae. Presence of mucilage clefts on remove the Anthocerotaceae from its posi­ the thallus and stomata on the capsule wall tion with the Bryophyta and lump it with are retention of a feature of early arche­ vascular plants, as was done by Mehra goniates. Sphagna, in retaining hepatic (1968, p. 24, fig. 9). Zimmermann (1952, features and the psilophytes, in lacking p. 464) wrote, " Parallel to the Rhyniaceae lignin, are other examples. Cytological and the Bryophytes developed from thalassio­ physiological resemblances between the phytic forms by relative dominance of the green algae and Embryobionta are the gametophyte". best examples of the retention of features Mehra and Handoo (1953) developed from the pre-archegoniate green ancestors the 'Antho-rhyniaceae' concept. Howe with the same cytological and physiological (1898, vide Cavers, 1911, p. 148) enume­ features. I (1981) named these early rated five peculiarities to distinguish antho­ ancestors as " green autotrophs". cerotes from rest of the Hepaticae. Of the Diametrically opposite views have been features enumerated by Mehra and Handoo expressed on the relationship between the four are more or less the same as those Anthocerotales and the Psilophytales. of Howe. Instead of the stomata on the Various authors have suggested the deriva­ capsule wall they added the low number tion of bryophytes or anthocerotes from of chromosomes in Anthocerotes. Goebel pteridophytes or the Rhyniaceae through (1905, p. 185) noted the deviations from regressive evolution (for references see the Hepaticae shown by Anthoceros and Takhtajan, 1953). Miller (1974, p. 166) wrote, "But a careful examination does wrote "Bryophytes in the broadest sense not show a resemblance with peculiarities are vascular plants from stocks which arose found in the Pteridophyta". in the early to middle Devonian from Mehra and Handoo compared the Rhyniophytina and Zosterophyllophytina". sporangium of Horneophyton with sporo­ I do not propose to add to what I pave gonium of Anthoceros and did not derive already written (1981) on this topic. the latter from the former taxon and Campbell (1895), on the basis of what he rightly so. They derived this stock from considered to be similarities between the the Chlorophyceae. sexual organs of the two taxa found kin­ Proskauer (1960, pp. 15, 16) wrote, "I ship between Anthoceros and pteridophytes. suspect that the anthocerotalean sporo­ Goebel (1898, 1905, p. 186) wrote, "The phyte is derived by reduction and specia­ kinship of Anthoceros to the pteridophytes lization from a sporophyte such as that of is then, so far as the sexual organs are Horneophyton...... In the case of concerned, a mistaken one". Bower (1935, Horneophyton itself the occurrence of p. 109) wrote, "Before basal intercalary forked sporangia represents indirect counter growth alone no morphological future seems evidence...... I do not wish to expostu- 96 THE PALAEOBOTANIST

late at length on the Psilophytic ancestory so, why such an important feature was of Anthocerotales. At present no firm lost in the Hepaticae and was replaced by proof can be brought...... I have no basal growth in the Anthocerotaceae ? quarrel with the postulated "Antho­ Steere (1969, pp. 137, 138) wrote, "It rhyniaceae" of Mehra and Handoo has been proposed by Zimmermann (1932) (1953) ". He also presented a pen picture and others who promulgate the analogy of "common ancestral denominator" for between isomorphic algae and bryophytes these groups. or protobryophytes were identical but sepa­ Mehra (1967, p. 50), on "common rate, and that the present-day epiphytic ancestral denominator ", quoted Proskauer habit of the sporophyte is derived or as: "A green parenchymatous land plant; secondary, and relatively recent. Although with stomata, single laminate plastids with space does not permit a full discussion • pyrenoid " presumably archegoniate, and of the merits of the case, in my opinion with alternation of generations". the idea is fallacious and should be dis­ According to Zimmermann (1952) origin carded ". of an apical cell capable of continuously Recently, I have re-confirmed lhat bryo­ cu tti ng off segments in a spiral manner, phytes are collaterals of green algae and was followed by internal differentiation pteridophytes, offered an explanation of into a central or medullary and a peripheral the origin of archegonium and concluded or cortical regions. This was an important that the advent of archegonium brought step in the evolution of the Embryobionta. about changes, which were not possible in It made possible the divergence between the oogamous green algae. Meiosis was oogamous and archegoniate plants as well deferred and the zygote continued to as the internal differentiation of the stem, develop into a new, hitherto unknown, its branches and the sexual organs of the entity - the embryo. Origin and evolution Archegoniatae. of an interphase became possible, the In the passage quoted above by Mehra function of nourishing the developing sporo­ no mention is made of an apical cell. It phyte, was passed on, mainly to the gameto­ is assumed that Proskauer's "common phyte. ancestral denomator ", in the absence of Bower (1935, pp. 142, 143) after discuss­ an apical cell, was not archegoniate. ing the embryos of Tmesipteris and Antho­ Proskauer, continuing (pp. 15, 16) wrote, ceros (a consideration which can include .. It is quite possible that the archegoniate the embryos of Sphagnum and Rhynia (cf. plants arose from a member of the Ulotri­ Pant, 1962) wrote, " It will be more instruc­ chales which not only possessed isomorphic tive to enquire what follows in each, as it alternation of generations but was itself passes to the adult state...... The alter­ su baerial and parenchymatous. .. .. Addi ng natives open to the epibasal half are either stomata, sex organs with sterile outer (i) direct spore-formation without branching tissue, etc. we arrive at the ., Antho­ or other marked morphological features rhyniaceae, but as a group with at maturity than intercalary growth, or apical growth free alternating phases, and thus by mini­ soon arrested; or (ii) morphological elabora­ mum deflnition a pteridophytic group". tion with continued apical growth and Again no mention is made of an apical branching, while spore-formation is cell. deferred. The former is the method of Mehra (1968, p. 23) on Anthorhynia­ the Bryophyta, with their capsules depen­ ceae concept wrote, "...... the haploid dent" on the gametophyte; the latter is the and diploid phases were morphologically, method of vascular plants with their more or less similar, independent and independent* sporophyte". photosynthetic. Both of them had apical In the light of these remarks is it fai-r cell segm~ntationand were radial in to remove the Anthocerotales from the organization...... The haploid phase Bryophyta and lump them with the Pterido­ possessed antheridia and archegonia " phyta? The place of the Anthocerotales, 'The Antho-rhyniaceae of Mehra and Handoo were archegoniate. It is difficult *It should not imply thaI Bower considered that to accept that the diploid phase in all the two phases in the Pteridophy1a were free from the early archegoniates had apical growth. If very beginning (see Bower, 1935, p. 139, fig. 103A), CHOPRA - STATUS AND POSITION OF HORNWORTS 97

with hepatic sexual organs, and the sporo­ unlignified. These elements in R. major gonium lacking in branching and apical and Nothia would then be very similar to growth, is with the Hepaticae. The place the hydroids of mosses. Indeed the stele of Rhyniaceae, with branched axes bearing of Rhynia as a whole may show an extra­ terminal sporangia and the archesporium ordinary resemblance to certain moss steles with a tapetum, as well as, the pteridophytic (figs 339-341). " archegonium of Rhynia is with the Pterido­ It is clear that Rhyniaceae resemble the phyta. mosses more than they do with the Antho­ Takhtajan (1953) compared the branch­ cerotes and that a moss type sporogonium ing axes of Horneophyton with branched is not handicaped by a basal meristem as sporogonia (teratologies) of mosses. apical growth of the sporophyte is the rule According to Mehra (1968, p. 9), " Merker in mosses. I am not tempted to suggest a (1959) interprets the creeping part in " Musco-rhyniaceous" stock, nor I suggest Rhynia and Horneophyton is the gameto­ an "Antho-sphagno-rhyniaceous" steck phyte and not the rhizome. . .. He con­ because I am fully aware of the limitations siders that a circumvellation is present at inherent in the diplophase of bryophytes. the region of the junction of the aerial The position of the anthocerotes vis-a-vis part with the prostrate one which is not other hepatics is the same as that of the case in a dichotomously branched Sphagnum vis-a-vis other mosses and the stem". Miller (1974, p. 162) credited to Rhyneophytina vis-a-vis other sub-divisions Lemoigne (of course with a note that his of pteridophytes. The resemblances bft­ interpretations are not fully accepted by ween the Anthocerotales, Sphagnales and palaeobotanists) on Rhynia as: "He has the Psilophytales do not warrant any unquestiona bly discovered both archego­ phyletic affinity between these three taxa n ium-like and antheridium-like structures, closer than what exists between the Hepa­ which are consistent generally with Merker's ticae, Musci and the Pteridophyta. Each observations". This confirms the dis­ one of the first three taxa is an early blind covery of archegonia in Rhynia gwynne­ offshoot from its respective stock. vaughani (Pant, 1962). Hebant (1977, pp. 108, 109, pI. 80) wrote, "It may be noted that the earliest known CONCLUSION tracheophytes were more similar in general appearance to certain present day bryo­ Bold (1956-57) modified the classical phytes than to most contemporary vascular concept of the Bryophyta by raising the plants. This concerns more particularly rank of anthocerotes, other hepatics and certain Rhynophytina such as Steganotheca mosses to that of three divisions. Steere or Cooksonia. Their tiny dichotomously (1958) did not concur with him and re­ branched axes with terminal sporangia are marked, " As a professional bryologist, on somewhat reminiscent of moss sporogonia. the other hand, I can go much further than (The latter are unbranched, but some Bold has and with equal justice raise other examples of teratological branching are highly distinctive groups of Bryophytes to known; in these cases, they are frequently divisional rank". I fully agree with him. dichotomous)..... , As pointed out earlier, I (1975) treated mosses as subdivision the internal organization of these early tra­ Muscophytina, and I still maintain the cheophytes, with a ring of outer supportive rank of a division for the Bryophyta. A cells and a 'simple' central strand, is also lot of information is needed to do justice more or less comparable to that of moss to splitting up of Bryophyta. In my opinion stems". a start should be made by defining the "With particular reference to Rhynia, it subdivisions and classes before the creation must be noted that Kidston and Lang of more divisions. (1920) failed to identify lignified secondary In 1967, I considered the Bryophyta to thickenings in the tracheids of R. major. be diphyletic and Steere (1969) considered Similar observations were made on Nothia them to be polyphyletic. I (1975) treated aphylla by A. G. Lyons ..... , Similarly, Musci as a subdivision. They are at least Proskauer (1960) suggested that the water­ triphyletic, Takakiophytina being the tbird conducting cells of R. major may have been suborder. 98 THE PALAEOBOTANIST

Subdivision Takakiophytina* -Prostrate or warrants the status of a class coordinate subterranean axes, lacking in leaves and with other classes into which the Hepatico­ rhizoids, with parenchymatolls apices, phytina is to be split up Sooner or later. bear erect leafy shoots with pyramidal or Resemblances between the two phases tetrahedral apical cells; mucilage pads on coupled with 5 or 6 chromosomes against the lower portions of shoots are composed 8-9-10 chromosome in other hepatics indi­ of crowded, numerous, multicellular and cate for this class a position at the very branched hairs, which may possibly be bottom of the heirarchy of the Hepatico­ homologous to moss rhizoids (though the phytina. functions of the two are different); leaf It seemS reasonable to presume that the development from a segment, besides un­ ancestors of modern Anthocerotae or paralleled form, is unique; oil-bodies are Anthoceropsida parted company from the present; antheridia are unknown; pedastaled stock/stocks that gave rise to other modern and spirally twisted archegonium recalls orders of the Hepaticophytina earlier than moSS archegonium and sporogonium is did the latter steck/stocks diverge to be the unknown. Under humid cultural conditions ancestors of mcdern orders other than the apices of erect shoots become parenchy­ Anthocerotales or classes other than the matous and often the oil-bodies are lost. Anthocerotae or Anthoceropsida. The chromosomal compliment, as a rule, is To sum up, Anthoceropsida or the K(n) = 4 = V(H) + V -.L J + J(h), or K(n) Anthccerotae, a class of Hepaticophytina, = 5 = V(H) + J + V j + V2 + J(h), though have been considered a synthetic taxon sometimes in T. lepidozoides an additional and much, that is unwarranted, has been " F-derivate" is present. read in the resemblances between this and Subdivision Hepaticophytina - The shoots other taxa. This class like the other Bryo­ whether erect or prostrate are with flat phyta is a collateral of green algae and the leaves, with genetically fixed apical cells in Pteridophyta. Ancestors of A nthocero­ both cases and so are the oil-bodies psida, presumably, were the first to part (except the Anthocerotales); all growth other company or diverge from the stock/stocks than that of the plant body is intercalary; that later diverged into other sections of elaters or pseudoelaters are almost invariably the Hepaticophytina. Modern hornworts, at present. the very bottom of the heirarchy of the Subdivision Muscophytina - Leaves are Hepatophytina, are a blind evolutionary line. flat, apical cells and oil-bodies are geneti­ I thank all authors whose contributions cally fixed; and growth (except some organs have provided material for this lecture, in Sphagnum) is apical; and elaters or particularly Prof. Kashyap, a pioneer bota­ pseudoelaters are always absent. nist and father of bryology in India; Diagnostic features of the three sub­ Professors Goebel, Bower, Campbell, divis.ions of the Bryophyta indicate that the Zimmermann and Dr Cavers. I am in­ Anthocerotales belong to the Hepaticophytina. debted to the Chairman and members of This is in conformity with the conclusion the Governing Bcdy of Birbal Sahni Institute arrived at while discussing the relationship of Palaeobotany for the honour they have of the Anthocerotales with rest of the conferred on me by inviting me to deliver Hepaticae on the basis of data and discussion this lecture on the birthday of the late (cf. Bower, 1935, p. 19: "the place of the Professor Birbal Sahni. Anthocerotales is with the liverworts "). Scion of a family of intellectuals, by his A combination of features seen in the qualities of head and heart, care for the Anthocerotales is not shared by it with progress of juniors, and courage to fight any other section of liverworts. This for upholding the right causes, he inspired many persons and endeared himself in *This diagnosis is based upon the contributions their hearts. I consider him a model to of Haltari et M. (1968, 1974) and Schuster (l966a). be emulated. REFERENCES

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