TWENTIETH SI~ ALBERT CHARLES SEWARD MEMORIAL LECTURE 1972

WATER : THEIR ORIGIN AND SPREAD

BY T. S. MAHABALE Professor of Botany, Maharashtra Association for the Cultivation of Science, Poona (India).

Published by BIRBAL SAHNI INSTITUTE OF PALAEOBOTANY LUCKNOW

ISSUED 1974 WATER FERNS: THEIR ORIGIN AND SPREAD

BY T. s. MAHABALE Professor of B:Jtany, Maharashtra Ass:Jciation for the Cultivation of Science, Poona (India).

Published by BIRBAL SAHNI INSTITUTE OF PALAEOBOTANY LUCKNOW TWENTIETH SIR ALBERT CHARLES SEWARD MEMORIAL LECTURE

VvATER FERNS: THEIR ORIGIN AND SPREAD

T. s. l\IAHABALE

MR. CHAIRMAN, COLLEAGUES, LADIES AND

GENTLEMEN

FEEL honoured by the invitation, that water is the very life itself, ']eevan' authorities of this Institute have ex­ as it is called in Sanskrit. No life I tended to me, to deliver the 20th as far as our present knowledge of Exo­ Memorial Lecture in the name of late Sir biology goes, exists without water. The Albcrt Charles Seward, my Profcssor's pro­ search is on, and one would know in future, fessor. I feel it all the more, because it whether there is anything similar to it on is here that I had my early lessons in other planets now, or had it in the distant Palaeobotany at the hands of Professor past. Various plant communities have ari­ Birbah Sahni, F.R.S. after whom this sen in water, prospered and have even Institute has been named. Work of it become extinct since ages. Some others has now increased many-fold under the have migrated to land taking temporary leadership of its present Chairman and shelter on the littoral zone, or on the banks active cooperation of highly trained workers, of rivers and margins of lakes. Others who have made a mark in the world of have not changed their aquatic habit and Palaeobotany by their devotion and dis­ habitat, as they found it more congenial tinctive contributions. To Indian Palaeo­ to live in water. Still others migrated botanists it is an academic home, a real land-wards. The conquest of land began Acad. There is no doubt that the Institute this way and terrestrial plant life came into will henceforth progress more and more. existence after a fairly long time when a Let all assembled here today wish it greater large proportion of oxygen released by glory, and work in future. accumulated in the air. The early The subject I have chosen for my lecture reducing atmosphere of the Earth made is of special interest, namely "Water way for the oxidizing atmosphere of it as Ferns ", as it touches both living and fossil now, and tolerance to it has been a great forms, and has provoked a number of step forward for the plant life. Here on problems yet to be solved. Watcr has land they rapidly prospered, and we have been the perpetual source for the origin, a continuous history of them for about organization, and continuation of plant 300 to 400 millions of years. But the life since the ages. It has also been a span of time preceding it is much longer, storehouse of many groups of plants. The 1000 to 1200 millions of years. However, seas, lakes, rivers, their banks, estuaries, not all plants were successful on land and mountain tarns, rapidly flowing cascades many of them reverted to aquatic life, and glaciers, each encourages unique assem­ marine or fresh water. Various taxa and blage of plants today. So they did in the plant communities adapted themselves to past. Therefore, it has been rightly said conditions of watery environment with 4 WATER FERNS: THEIR ORIGIN AND SPREAD varYlllg degrees of tolerance, and they got Intertrappean Series. They have been spread from highly luxuriant tropical forests named as Rodeit.:.s by Professor Sahni to desiccated deserts. (1943) aftu the distinguished Indian geo­ The aquatic plants on land naturally do logist, Professor K. P. Rode of Udaipur not have continuous distribution but are University. Members of the other family segregated into communities at various , and Salvinia, occur, places in lakes, on river banks, estuaries, on the other hand, much more widely in mountain lakes covered with snow etc. U.S.A., U.S.S.R., in Great Britain on the The limiting factor for their spread natu­ Island of Wight, in Holland, Australia, rally is water. Should such isolated plant mostly from post-Cretaceous period till now. communities be cut off from each other Naturally such a distinct group continuing or be dried up for any reasons, they become till today is expected to have a continuous progressively less and less in number and history; but alas! such an expectation is their population decreases, and they become far from being realized. sparse. Some become rare and have to The distinctive characters of the group face intensive competition from other Hydropteridinieae, are heterospory, sporo­ aquatic biotic groups of plants and carps and aquatic habit. It is a highly animals. Ultimately they become rare artificial unit, as quite unrelated groups and eventually disappear on land. After of plants grow together as an aquatic com­ all rariety is undoubtedly the fore-runner munity in the same place. This has tickled of extinction. This in short is the general many botanists, and made difficult to trace story of biology 01 water plants. As a their origin and relationships. In the earlier rule they are wonderfully well adapted to works on Ferns it was customary to recog­ their environment, e.g. mangroves, cacti nize them as a single group on par with and other plants growing in the deserb of the Eusporangisteae - another very pro­ Arizona, Kizil-Kum and Rajasthan, or the blematic and heterogenous group, and the Alpine plants. The water ferns are in no Leptosporangiateae forming the majority way different than others and have to face of present day ferns. The Rhizocarpi or the same fate in course of their wanderings Hydropteridineae as they were called, are on different continents in different eras. not related to each other among themselves, They are a small group of Filicales and although they have two common characters, are supposed to haVe come into existence heterospory and sporocarps. Both families during the last part of the Cretaceous have leaf characters and anatomy modified period. They have no direct relations to suit the life in water and for dispersal. earlier. They are supposed to be a high­ Their original characters are masked by the ly evolved group amongst ferns. They reduced characters due to aquatic habit and comprise two small families, the Salvinia­ it is difficult to decide what characters are .ceae and Marsileaceae. Of these the Sal­ really conservative. They comprise only viniaceae appear:; to be earlier as it occurs a few genera. The Salvaniaceae has two in the Uppermost Cretaceous period. A genera: Salvinia with about 10 species and few fossil spon:s such as A rcellites (Pyro­ Azolla with about 6 well recognized species. bolospora) are claimed to be belonging to The Marsileaceae has three genera: M arsilea the Marsileaceae. They occur in still earlier with about 70 species spread all over the strata of Holland, Belgium, U.S.A. etc. world, many of which are found in Australia, But the memberspositiv(Jy belonging to Pilularia having six species found in Europe the Marsileaceae are known only from the and America, and Regnellidium having one Tertiary strata of India in the Deccan species endemic to Southern Brazil. We \V.HER FERNS: THEiR ORIG1N .\ND SPRE.-\D 5 have only small material for comparison, in salt marshes in the tropical seas. It and, therefore, analogies drawn mainly produces golden coloured sporophylb and on the basis of a common structure such as has striking spores. Its sari are distributed sporocarp \,vould be erroneous. At the all over the back side of leaf in a charac­ same time suggested relationship of the teristic manner and its spores are typically Salviniaceae with Hymenophyllaceae, and trilete. They are known to be 'present in of ~Iarsileaceae with the Cyatheaceae or the Lower Miocene pollen Bora of the Schizaeaceae often becomes a scholastic Klodnica Valley of Upper Silesia. Two effort. Hymenophyllum has 13 as the basic fossil species of spore~ arr rE-cognized. One number of chromosomes, whereas Azolla is identical with the spores of ACl'ostichum has 11 and Salvinia has 9. In the majority aureum and the other with those of A. of species of M al'silea this number is 20. axillare occurring at present in Java, Su­ In Regnellidium it is 19. In Schizaeaceae matra, Borneo, India and Ceylon. The basic number is 10, and the other numbers latter species, like its counterpart, is not a known are 10, 77 and 38. In Cyatheaceae, mangrove but an epiphyte growing on the which are tree ferns, n = 35. To these branches of trees in deep tropical and three genera of the Marsileaceae one has sub-tropical forests. In the Indian Ter­ to add an extinct form genus, Rodeites, tiaries these spores have not yet been irrespective of its taxonomic status whether recognized, as very little is known about as an independent genus or as a species of the tolerance of these species to the degrees Regnellidium. This point will be discussed of salinity. Consequently the limits of later. their zonation along sea coast and estuaries Ferns as a group are essentially shade are not known. If cultivated A. aureum and water loving plants. Their real home also grows as a fresh water . is tropics where there is maximum concen­ The other water fern Ceratopteris prefers tration of genera and species as Manton fresh water marshes and lakE-so It is a and Sledge (1954) found. In Temperate small genus with about four species spread regions the density of population of a parti­ all over the world in tropical and sub-tropical cular species in an area of comparable size waters in the Old and New \Vorld, and also is more, but not many genera and species in a few temperate lakes. Its spores occur occur there. Among \-vater ferns Azolla in various Tertiary and Quaternary for­ and Salvinia grow Boating as segregates in mations and have been reported from the isolated ponds. M arsilea and Pilularia form Oligocene rocks of Barails of Nahorkatiya continuous stretches on edges of lakes, region of Assam by Ghosh (1941), Raksi rivers and Nallahs, rooted in wet mud. (1962), Bis\\"as (1965) and others under the Regnellidium and Pilularia grow similarly name Cicatricosisporites. Sah and his asso­ but do not stand competition from others, ciates Dutta, Kar and Singh (1966, 1968, and very often die due to attacks by aquatic 1971, 1972) have shown that they are the fungi. same as of Ceratopteris and named them Besides these well known five genera of C. macrocostata. Baksi (1962) found that water ferns, there are a few other ferns these spores range from middle Oligocene which grow as hydrophytes or hygrophytes to Miocene. They occur in the Miocene thriving partly or fully in water. Growth of Gujarat also and in Makum-Namdang in water is a necessary condition for the area in East Garo hills. The first definite completion of some stage in their life cycle. record of it is from the Lower Eocene of Two such important ferns are Acrostichum Tura Formation of Garo Hills. Dr. Sah's and Ceratopteris. ACl'ostichum aureum grows work suggests that the different spore forms 6 W-\TER FEfu'lS: THEIR ORIGIN AND SPREAD of this genus serve as good markers for the from the above that all these Leptosporan­ different formations in that area. It has giate ferns growing in steady or rapidly helped in stratigraphic correlation of Ter­ flowing waters, partially or fully, are for tiary sedimentary sequence of Assam. Some some part of their life aquatic or semi­ fossil spores related to Cel'atoptel'is have also aquatic. They share watery habitat as been described under the new genus /'11 ag­ a common feature with the Hydropter­ nastriatites, N1. howardi by Germeraad et al. dinieae; but that need not suggest affinities (1968). This spore marks the Oligocene­ inter se, as they are homosporous. 'We Miocene horizons of tropical South America, have, therefore, to treat the member" of Africa, and South-East Asia. It is interest­ Hydropteridineae each separately. ing to note in this connection that this Pteridophytic spores are known to occur fern spore is a marker of sedimentary in various strata of the Earth, and have sequence in Oligocene-Miocene horizons in vertical as well as horizontal distribution. India also. Being a water fern it cannot They are good markers of time and strata. migrate like other terrestrial ferns and as From this point of view, the families Par­ such it produces several bioforms. As it is keriaceae and Schizaeaceae seem to be of very variable, the affinities of Ceratopte1'is special interest as they occur in the possible as Holttum (1954) points out are not clear. oil-bearing strata of Miocene and Pliocene Besides these two ferns some other ferns strata. The work of Dr. Ghosh, Dr. Baksi grow on river banks and estuaries and in (1962) and Drs. Sah and Kar (1971) of this areas periodically flooded with water, such Institute on the spore forms of Ceratopteris as banks of rivers and Nallahs, in deep is important in co-relating the horizons in tropical jungles. Here these ferns live as different areas, particularly when mega­ hydrophytes in inundated condition for fossils or impressions are not available. some months. As the water recedes, they As a matter of fact this is the special ad­ produce sporophylls and complete their vantage of paleopalynology over other dis­ life cycle. They are: Humata, of which ciplines, as even a small sample of a few one species occurs in Nilgiris, Khasi Hills miligrams helps to unearth vast information and Bhutan. Diptel'is lobbiana is deeply about the sediments and conditions under rooted in crevices of rocks in Malayan which they were laid. Hence they are jungles and for a period it gets inundated likely to prove of considerable help in oil on flooded rocks. osmunda l'egalis and and coal exploration. Thelyptel'is ciliata grow under similar situa­ A spore is an extra-ordinary organic iion. M acrothelypteris ornata and 111. unit of life, being an haploid cell. Botanists terresiana grow close to streams in mar"hy working on living plants consider it as a areas, usually isolated in Khasi and Jaintea definite entity having a definite function Hills in Assam. Many rivers of Deccan in the life cycle of a plant. Some think arise at high altitudes in Western ghats. it to be the first cell of the gametophyte There are three or four ferns here which itself; whereas others think it to be a pro­ grow in a similar way. They are Ampelop­ pagule which on its germination gives rise teris pl'oiifera, Egenoljia asplenifolia, E. to gametophyte. From the view point of appendiculata, Gymnopteris contaminans, a living plant, its function is two-fold: to Schizoloma ensifolia and S. heterophyllum. disperse plant in new localities and to It is quite possible that their spores may produce gametes. The small ones ranging be found in fresh water sediments of Assam from 10 to 30 [J. are considered as micro­ and Nilgiris, as these are the genera that spores, meaning thereby that they are not still occur in those areas. It will be clear only small-sized spores or miospores, but "VATER FERNS: THEIR ORIGIN .\ND SPRE.\D 7 also ones which give rise to male gameto­ as Ceratopteris is known to have two chromo­ phyte and male gametes. On the other somal complexes n=40 and 77. It also hand, megaspores are large and range from shows physiological heterospory, and pro­ 50 to 150 fJ. or more, and give rise to female duces a variety of prothalii. Some of them gametophyte. In Algae and Fungi there have midrib with reproductive organs and are many other kinds of spores besides wings with stomata (Mahabale, 1948a). these, which have a specific function e.g. Its leaves are dimorphic and venation zoospores, uredospores, teleutospores, etc. complex - reticulate. It grows rooted in During sporogenesis spores assume their aquatic mud and even floats on the surface definite shape after the polarity is estab­ of water in some Assam lakes. When lished. Their polarity according to me water begins to recede it migrates to rice is fixed at the time of tetrad division. The fields and produces sporophylls and prothalli. pointed end where four spores meet in a Thus its shape and size, chromosomes, tetrahedron is proximal, and the other nature of annulus and sori, size of spores, rounded end is distal. First division in pro thalli greatly vary. It is no wonder germination and the way in which the first therefore, Miocene strata of Barails, Tipam cell emerges out of spore is indicative of and other places in Nahorkatiya basin have their polarity. Sporodenn gets differen­ yielded differently marked spores of different tiated after the polarity is fixed. The sizes in vertical and horizontal distribution. palynologists make most of sporoderm cha­ Only a few spores of pteridophytes have racters overlooking the functional aspect played such an important role in strati­ of spores and base their conclusions regarding graphic and biological considerations as the identity or relationship of spores very that of Ceratoptcris. Leaving these aquatic often out of proportion. This should serve and semi-aquatic ferns we may turn our as a caution to those who deal with" Sporae attention now to the two members of the dispersae ", and who out of necessity talk Salviniaceae. of isospores, miospores and macrospores The genus Snlvinia has ten species spread in a different sense. To them the spore is mostly in tropical waters. Only S. natans merely a kind of rock·content like a mineral has far wider geographical distribution in having a particular size and which indicates Temperate regions in Europe and Australia. its composition, age and mode of sedimen­ It occurs in fossils and about 20 species tation. In doing so they forget that the have been recognized. They fall in three spore they are dealing with had a function categories: those with oblong leaves, those in the life cycle of the plant to which it \vith upturned leaves, and those with cucu­ belonged, and, therefore, it has to be treated late leave,;. They produce distinct bioform<, differently than minerals, as a live entity which are not stable. The hairs on the of the past. It is not merely a haploid leaves in different species form a distin­ cell of cytogenctists or a propagule of eco­ guishing character. However, many of the logists or a marker of stratigraphists, but species and plants in different areas are an entity having many functions of its own. sterile. as the meiosis in them is irregular And therefore, while dealing with them, (Mahabale and D'Mello, 1952; Loyal and their full significance must be understood. R Kaur 1964). Their megasporoscarp con­ The spores of Cerato)Jtcris are highly signi­ tains a single megasporangium with one ficant in this context. Their size, markings megaspore fully ripened. IVlegaspore in all on sporoderm di ffer in different living species has three-la:,wed \vall. The outer­ species, so they did in the past in different most is perisporium \\'hich is spongy and Tertiary strata. This is not surprising, facilitates their floating Oil the surface of 8 W.\TER PEHNS: THEIR URIGIN AND SPlm,\D water and helps in dispersal. Many oil like Salvinia oblongifulia and comparison globules are present in the distal part which of it with the known fossil species will are consumed by the developing sporophyte throw some more light on the problem formed after fertilization at the apical end which is too well-known to the students of of the megaspore. The microsporocarps~1 palaeobotany in India viz. presence of are many III a chain and each sporocarp South American element in the Tertiary contains massulae in which the microspores· ',ora of India. arc embedded. They are of two types in Other floating genus of the Salviniaceae the genus. In a species like Salv'inia natClnS is Azolla. About six species of it are found a massula occupies the entire c,wity of the in the 'warmer parts of the Old \VOIld and sporocarp after germination and forms a in the Temperate region of Europe, America solid frothy mass. This generally happens and A.ustralia. The genus is very susceptible in fertile species. On the other hand, in to cold, and quickly dies \vithout producing sterile species like S. cueulata or in many fertile plants in different populations. It plants of S. auriculata the megaspores arc grows best in tropical \\'aters. Africa is lnfertile due to meiutic irrcgularitic~. The supposed to be its original home, The microsporucarps produce massulae which genus is divided into b\ 0 sections: Eu­ are hollow and they float on the surface of Azolla which has glochidia in massulae water. In 1Y35, Professor Salmi observed anchor-shaped, and 3 or 4 float corpuscles. some small seedlike bodies in some cherts Azolia jiliculoides, A. caroliniana, A. rubra, collected at Sallsar (M.P.). The shape of A. M exicana belong to this Section. In sporoderm of the megaspore in them was the second category of species massulae peculiar, and it looked as if they were have curved llair-like glochidia and 6-9 or integumellts of a small seed. These bodies, iess float corpuseles as in A. pinnata. Azolla therefore, were named as Sausarospermum. jiilculoides complex is of world-wide occur­ He (Salmi, 1Y43) also instituted genus rence being present in Austrillia also. The Afassulites for the hollow milssllla of some A. pinnata is mostly in Volga basin, water fern, then not known in the living. Australia, Indiil and Japan. The third Later on, however, when I investigated complex is formed by A. Ililotica which is a three species of SalvillZ:a, S. natans a fertile South African species from Rhode~ia de­ species, S. cuculata of Sunderbans which scribed by Demalsay (1 Y53). It also pro­ is sterile, and S. auriculata from Brazil duces different clones and varieties. The \-vhich is also mostly sterile. I found that glochidia are absent in it and float cor­ the megaspore of the introduced Brazilian puscles arc 8 or less. In Eu-AzoLla generally species S. auriculata is identical with Sausaro­ there are four float corpuscles and in the spermwn in all details and that the massulae other Section Rhizosperma there could be in that species arc not solid as in the fertile more, as many as nine. The float corpuscles S. natans, but are hollow as in JVI asslll.ztes serve as a pedestrial to the megaspore and coelatus of Salmi (l\:Iahabale, 1954b). S. upraise the gro\l'ing sporophyte. Glochidia auriculata is believed to be a tetraploid of microspores attach themselves to the species, but probably produces some fertile glochidia found on the basal part of the and some infertile races. The interesting megaspore, fixed in the midst of float fact is, the Paleocene species of India, corpuscles. It 0PCllS at the top exposing S. intcrtrajJjea, found in the Deccan Inter­ small gametophyte. The microspores come trappeans, sho\\'s strong resel1l blance wi th out of microsporangium and their contents the present day South Brazilian species. hreak into small segments forming massulac Further investigation of other fertile species with glochidiil. Glochidia with microsporcs WATER FERNS: THEIR ORIGIN AND SPRE.\D 9 get attached to them and germinate in the 1969). There are three broad complexes. vicinity of megaspores to which they are Pre-Tertiary Azollas have float corpuscles, attracted presumably by some sort of generally 3 or 4 or sometimes less and chemical "timulus. Float-corpuscle" merely glochidia once or more septate, and the tips help the megaspores to float. :\Iicrospores anchor-shaped. Upper Cretaceous Azollop­ germinating in the vicinity of megaspores sis has multibarbed anchor-shaped glochidia release sperms near female gametophyte and many floats. They broadly can be which peep out of the megaspore with one or said to belong to the present day A. jili­ two archegonia. After fertilization megas­ culoides complex. In the second, A. pinnata poresinks below the level of ~water, quite often complex, the glochidia are without anchor reaching the bottom or edge of the shallow tips and have 8 or 9 float corpuscles in pond in which the plants grow. Segmen­ megaspores: The third complex is formed tation of the fertilized egg does not begin by Azolla nilotica of Africa. There are no immediately. For some time oil globules glochidia in it and the number of float in megaspore are utilized by the fertilized corpuscles is more than 4, 8 or 9. All egg. The megaspore becomes light and the known fossil Azollas belong to either comes to surface undergoing rapid cell " Filiculoides" group or Azolla pinnata divisions. Thus both in Azolla and M arsilea group. The Pre-Cretaceous Azollas had the fertilization and developmental mecha­ more than four float corpuscles. But all nism of sporophyte is the same, highly the Tertiary Azolla. species concentrated in adapted to floating at the surface of water. the Miocene or post-Miocene period and Reduced stelar system, floating leaves, have anchor-shaped glochidia e.g. Azolla aerenchyma in stem and other parts, profusely prisca of Island of Wight, London Clays, branched roots as well as light sporocarps A. primaeva, A. caroliniana of U.S.A., A. are similar adaptations in both to resist rubra of Australia and A. intertmppea of water. Their vegetative part:, are highly India all belong to " Filiculoides " complex, adapted to living in water, but the repro­ but they had variable number of floats. ductive mechani"m is very conservative. A. prisca had 9, A. teschiana 2-4-9, A. It has no parallel in ferns. On the basis primaeva 3, A. antiqua 9. A zolla pinnata of anatomy, simplicity of vegetative parts, is found in post-Miocene period. Both the fluffy wall of sporocarps, position of sori at Azollas, A. pinnata and A. jiliculoides, are the tips of veins have suggested affinity of found in Holland, Germany, Volga basin the Salviniaceae with Hymenophyllaceae. of U.S.S.R. and Japan (see Dorofeev, 1959; But it seems to me that their simplicity Hall, 1969; Hills & Gopal, 1967). Some are has been achieved mainly through reduction. intermediate in characters e.g. A. montana, The chromosome numbers found in the A. primaeva, A. prisca. The genus is thus Hymenophyllaceae are n=13, 18, 21, 34 very variable as regards glochidia and floats whereas Azolla has n=12 and 22, Salvinia and is also far flung in distribution and is has n=9 or 18. The venation of the leaf supposed to have migrated from Africa. in Hymcnophyllaceae is open, while that It is difficult to imagine that Azolla nilotica in Salvinia and Azolla is closed. They, endemic to South Africa could be the therefore, do not seem to be related, at any ancestral form, and could have given rise rate closely to the Hymenophyllaceae. to present day Azollas as 'well as the past Azolla is essentially a Tertiary genus and ones belonging to two complexes 'Fili­ 10-15 variable species are known from the culoides' and 'Pinnata', and the inter­ horizons ranging from Cretaceous to Pleisto­ mediate ones also. More evidence would cene (Sahni, 1941; H. S. Rao, 1935, Hall, be necessary for accepting such an idea, 10 WATER FERNS. THEIR ORIG[N AND SPRL\D as no fossil AzoUa is known from Africa. Despite this, one gets no conVIctIOn that None of the fossil species whose repro­ they really are the members of the Marsilea­ ductive organs are known show similarity ceae. According to Dr. Mrs. Chitaley spores with the massulae of AzoUa ni/.otica (Maha­ Pyrobolospora lobata described by Dijkstra bale, 1954a and 1954b). (1959) seems to agree \\'ell with the spores Second family of the Hydropteridineae, of Rodeites, but nothing could be said }Iarsileaceae has three members; M arsilea definitely about them. The third genus with about 70 species of \\'hich 57 are well RegneUidium has unique spores and sporo­ recognized and spread all over the world carps. Like the sporocarp of Marsilea, in the Tropical as well as Temperate waters. its sporocarp is bivalved but round; the The majority of species however, occur in raphe is small and \I'ithout teeth. Its Australia. Pilularia with acicular leaves symmetry is bilateral. The mechanism of has six species mostly in Temperate waters, dehiscence of the sporocarps in Regnellidium and Regnellidimn from Brazil is monotypic and M al'silea is alike by the outthro\\' of having only one living species, A. diphyllmn. a mucilagenous cord having t",o ro\\'s of To these Dr. Mrs. Chitaley has added sori. The sporocarps in Marsilea and Reg­ Sahni's form genus Hodeites as a distinct neUidium produce a variable number of genus of the :Marsileaceae on par with the sori in a sporocarp and each sorus contains tluee other genera. According to her it a variable number of megaspores total per combines the characters of M ars-ilea and sporocarp, ranging 2 to lOin M arsilea and Regnellidium. Sahni thought it to be a upto 90 in RegneUidium, all studded in the distinct fossil species allied to Regnellidium midst of numerous microspares. The num­ diphyllum. Chitaley and Paradkar (1971), ber of sporocarps and megaspores in a however, feel that it is a different genus sporocarp in some species of iVlarsilea, 1\1. of thl: Marsileaceae. This is no doubt due minuta, M. quadl'ifolia. M. erosa is variable. to confused and imperfect understanding The Ilumber of ::.porocarps borne at the of the characters of the two genera. Many base of the petiole b also different in diffe­ botanists would rather agree with the original rent species; in some only one, in some two, vie\\' of it of Profe""or Sahni for very strong and in some many on the petiole of each rea'OI1" Pilulal'ia \"ith its leaf morpholugy, leaf. In Regnellidium diplzyllum there is radial symmetry of sporocarp - its burrow­ only one sporocarp at the base of each leaf, ing habit, imperfect mechanism of dehi­ but in the fo:,sil form genus Rodeites the sr.~nce of the "porocarp, and disper.sal of number seems to be more as in Marsilea spores by developing cracks into it on polycal'pa. The megaspores in a sporocarp decay, undoubtedly suggest that it is a are also variable about 90 and they have primitive member in the family. It has peculiar appendages at the apical end. three doubtful fossil species (l\1ahabale, 1958). In the Tertiary form genus, Rodeites, the T11e genus M arsilea 11 as ten doubtful number of megaspores in a sporocarp, is fossil species; but it is necessary to re­ very large. But no complete reconstruction member that many of the earlier fossil of this water fern has been made. Till records are in the form of leaves previc..usly then perhap!:> it would be better not to described as Sagenopteris, which is no create a new synthetic genus far it, beca­ longer considered to be a fern. Some use, on the Whole, in Evolution divergence megaspores named as A rce/lites (Pyrobolo­ of Characters i" more common than their spora) have been reported from Lower synthesis. And, therefore, to consider Cretaceous and other horizons, and they Rodeites as a new synthetic genus merely are similar to tbe spores of Marsileaceae. on the similarity of characters between WATER FER.NS: THEIR ORIGIN AD SPREAD 11 l?odeites, J11 arsilea and RegneUidium is a from India to America. To my mind, this matter of opinion. has something to do with the foundering of It may be pointed out here that a vast the Gondwana continent where it must amount of work on the morphology and have been in existence before and subse­ cytology of ,VIarsiler. ha; been done, as quently wandered. The African continent also on the morphogenesis and biotypes. is supposed to be the home of Azolla which The chromosomes recorded in it vary­ has also migrated Eastwards, Westwards generally 11=20, sometimes 36, 40, 105. and Northwards; but since no fossils of In Regnellidium they are 19. In 1}1 arsilea Azolla, M arsilea or RegneUidium have been there is both irregular mtiosis, polyploidy, found in that continent, this will merely aneuploiody and parthenogenesis which was amount to guesswork. The mechanism of first observed by Strasburger (1907). Mor­ spore dispersal in Regnellidium and M arsilea phogenetic studies on it show that the is also quite unique in ferns (Mahabale. genus is highly susceptible to external 1968). Their sporocarps have the capacity factor::> and produces in vitro, and in nature, to remain dormant for years. The spores various biotypes and unstable forms. Re­ grow even frOI11 sporocarps obtained from gnellidium diphyllum also yields to morpho­ some old herbarium sheets. This is pro­ genetic treatment producing variable bably due to their compaction in mucila­ structures. Recently Dr. Loyal of the genous mass protected by thick wall of Punjab Univer::>ity was able to obtain in the sporocarp. Under conditions of desic­ culture a haploid plant of it. All this cation in Rajasthan desert M arsilea aegyp­ ought to suggest that convergence of cha­ tica preserves contents for years, and on racters rather than synthesis of divergent return of favourable conditions germinates characters has resulted in the production quickly by imbibing water by the muci­ of a form genus like Rodeites. Obviously lagenous cells and hairs on the sporocarp t here is need for further studies on RodeiLe$ wall. The morphology of this organ is in a ncn-commital way, and also on Regnelli­ highly controversial and attempts made dium diphyllum. to homologize it with the sari - bearing As early as 1948, I (Mahabale, 1948b) organs of the Cyatheaceae or Schizaeaceae had pointed out that the genus Regncllidium is not \ovithout lacunae. I would rather is quite unique in many respects among prefer to consider it as an organ sui generis, ferns. It is the only genus of ferns which remnant of some ancient fern fructification, has latex and laticiferous tissue system. rather than attempt to homologize it with It poses many other problems too. One that of some highly differentiated modern of them is: how a Tertiary fern in the ferns. Some have compared it even with Deccan Intertrappeans of Inia and living the seed capsule of angiosperms, but this Regnellidium of South Brazil could show seems to be a far fetched comparison, great similarity, despite their occurrence just as it would be to consider Azolla and in two different countries of Southern Marsi!ea related to each other, simply hemisphere, separated by two oceans and because both possess heterospory and sporo­ a continent in between. Could they have carps. The morphology of sporocarp migrated from some common source in suggests that in Salviniaceae it represents the mid-oceanic islands, now no more, in a soral envelope enclosing sorus, whereas two directions westward to south America, in Marsileaceae it represents the whole of and Eastwards to India;> It is difficult sporophyll, bearing several sori in positions to imagine that this Tertiary species of not yet satisfatorily explained. As a India Rodeites dakshini could have migrated matter of fact these two different ways of 12 WATER FERNS: THEIR ORIGIN AND SPREAD bearing son IS an age-long practice. Some two species of fern 5tauropteris, S. oldhamia sporangiferous organs of the Devonian and 5. burntislandica differed to some extent genera bore them on organs of intermediate from each other. The microsporangial wall nature which cannot be categorized as in S. oldhamia was multiseriate, but in stem or leaf. The fact is, various taxa of 5. burntislandica it was one-celled. Another ferns evolved broadly on these two lines, main difference between the two lay in but similarity as well as deviation from their megasporangia. Hensonites is con­ them are not without significance. They sidered to be a megasporangium of 5. indicate parallel tendencies in evolution. burntislandica. It had two megaspores well Therefore, too much of phylogeny should developed within a megasporangium, lodged not be seen in them in order to fit them over a loose epithem-like tissue. Some into our phylogenetic systems with perfect times there were in addition one or two harmony. small possibly abortive spores. Chaloner The major problem, however, they both (1958) confirmed this and further found provoke is that of heterospory - apart that there could be two large megaspores from the nature of sporocarps, extraordinary and two minute presumably abortive spores. mechanism for fertilization and spore dis­ The sporangial wall though cutinized had persal by a mucilage cord. Heterospory no definite mode of dehiscence. Sporan­ has been in vogue since long time from gium was shed intact in soil and megaspores Devonian. It has been pre~ent on a large were released by decay and disintegration scale in Green, Red and Brown Algae. of the sporangium wall Like the sporocarp One visualizes a floating mass in sea in wall of Pilularia. A large number of such which many plants had heterospory both megasporangia, Bensonitcs, are some times in the physiological and morphological obtained in the same matrix. Some of sense. Also there were zoospores, isospores these meg

Gleicheniaceae, Schizaeaceae. Many things The sporangial wall in Salvinia likewise are common between the Coenopteridaceae is simple and profusely hairy and even and Eusporangiateae, and between Coenop­ possesses stomata. It would be worth­ teridaceae and Salviniaceae. Similarly there while searching them in Bensonites also. is a good deal of similarity between the Sporocarps in Marsileaceae on the other Marsiliaceae and Schizaeaceae. But how hand, its general organization of l~af, stem, the Coenopteridaceae, which is earlier than anatomy are similar to those in Schizaeoid the other three major fern taxa Osmun­ ferns like Lygodium, A neimia and Schizaea daceae, Gleichcniaceae and Schizacaceae, and even Ceratopteria. The probability, is related to Hydropteridineae is not very therefore, is that for the origin of heteros­ clear. Possibly we have to derive Salvi­ pory, at least in the family Salviniaceae, niaceae from heterosporous Coenopterid like we have to look to heterosporous Staurop­ S. burntistandica, though not directly from teridineae. For that in the other family, it. Both have extremely simple tripartite :Marsileaceae, we have yet no clues. Herein leaves, dichotomy or trichotomy of stem lies a great opportunity for work to modified heterosporous sporangia, which pteridologists, palaeobotanists and physio­ are extremely simple in S. burntislandica. logists.

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