The Questionable Origin of Early Land Plants from Algae

The Palaeobotanist, 28-29: 423-426, 1981. THE QUESTIONABLE ORIGIN OF EARLY LAND PLANTS FROM ALGAE F. P. JONKER Laboratory of Palaeobotany and Palynology, The State University of Utrecht Heidelberglaan 2, The Netherlands ABSTRACT The paper deals with the rise of terrestrial plant life in the Early Devonian. The view is developed that apart from Psilophytes some algal groups may have given rise to (semi-) land plants. (Semi-) land algae, however, have not been successful in competition with land invading Tracheophytes and became extinct after a relatively short existence. Key-words - Algae, Early land plants, Terrestrial vegetation, Psilophytes, Early Devonian. 5lTU'll'li ~ tftlif 'fiT JiTcm;iT ~ ~ ~W.f - 1'%0 tfto ~ ~ mlt-qz;f 5lTU'll'li ~ iT ~ 'TT~-;;r')q.; ifi ~ ~ w<rf.mr ~ I ~ ~ Olf'ffi f'f;m 'flIT ~ fif; l;li'.5'tl!flI<;<i)li'iifi ~rncr ~ ~ <!~ ~ '+IT (ri) "!-~ 'fiT ~ gm ~ I cr~, ~r ~!flT~ ifi ~ iT (>;f~) ~lf!lT9m~!fl<'f;r@ ~ crqf >;fq-~ >;J~q'lllf"l'll ~ ifi w:rrq: ~ \[1 'Tit I The two above mentioned papers prove J.whatM. SchopfI presume(1978)wasshowedhis finalthatpaper,the again that some knowledge of modern larger INtill then enigmatic, North-American, algae, their life form, and their reproduc• Devonian genus Foerstia White belonged tion and life cycle is needed in studying to the Phaeophyta and should be regarded and interpreting Silurian and Devonian as a marine "fucoid". The presumed plant megafossils which are too often attri• spore, or megaspore, tetrads represented buted to Psilophytes or other Pteridophytes. egg cells of which the coats were resistant. Another question in connection with These eggs, borne in fucoidal conceptacles, these fossils, however, arises, in regard to might be forerunners of the more l'educed which problem numerous suppositions have oocytes that occur in modern Fucales. been published, viz., did these algae represent The thallus of Foerstia lacks a cuticle early land plants or at least temporarily and it has internal filamentous pseudo• emerged and at other times submerged tissue like Fucus and other fucoidal brown plants. The sudden rise of land plants algae. in the Devonian, belonging to different A yeal' later, Jonker (1979) developed divisions of Pteridophytes, is apparent. the view that the Early Devonian members It is, generally, attributed to a gradual, also of the enigmatic genus Prototaxites "genesis of atmospheric conditions suitable Dawson were Rhodophyta-Nemalionales to terrestrial plant life. It might be that with stout, erect, branched, winged cauloids, this atmospheric change also produced a the wings in some places expanding into certain effect on some groups of algae, phylloids, while terminal phylloids also giving rise to different groups of land algae, occurred. The phylloids were described or at least algae tl'ansitional from water before as Nematothallus Lang and the cysto• plants to land plants, but then apparently carps as Pachytheca J. D. Hook. to unsuccessful (semi) land plants that be- 423 424 THE PALAEOBOTANJST came extinct after a relatively short infer the existence of large land algae in existence. Devonian times. Brzyski (L976) was of With regard to both Foerstia and Proto• the opinion that Prototaxites and Pachytheca taxites, Gray and Boucot (L977) argued were parts of the same plant. A partial that the "Nematophytalean tracheid-like fusinization of his Pachytheca and Proto• tubes" as found in the cauloids and taxites specimens indicates, in his opinion, phylLoids of these genera, may have had that for some period of time the dead plants a functional role similar to that of tracheids, had not been immersed in water. Either i.e. they may have been water conductors, a they have been washed ashore or the water circumstance only expected in a land receded from their habitat. A third, ac• plant or possibly in an emergent aquatic. cording to him least likely, explanation is They attributed the two genera, together with that it concerned land plants. In a later Protosalvinia Dawson in which genus they phase the fossilization took place in water included Foerstia, to the Nematophytales under reductive conditions, during which Lang, an order of land algae and more the remains became pyritized. According or less intermediate between water and to him the fossils in question were, con• land plants or between algae and vascular sequently, at least once redeposited, and plants. submitted to two successive stages of fossiLi• In his above mentioned paper Schopf zation. (1978) strongly opposed to Gray and For further details and literature I refer Boucot's concept with regard to Foerstia. to Jonker (1979) who himself held the Foerstia should be regarded as a marine opinion that the plants occurred in dense fucoid and, according to him, there is no vegetations, tightly packed in muddy tidal evidence that these plants have ever been flats or lagunes, temporarily emerged and anything but marine. Foerstia remains have at other times partly or totally submerged never been reported from a nonmarine as the transport of rhodophytalean sper• association and this statement contrasts matia, carpospores and tetraspores require with Gray and Boucot's view when they submerged conditions. He also expressed compared marine occurrences with that of that in all probability the same way of life occa~ional pieces of drift wood of Calli• - water pLants adapted to periods of xylon. drought and permanently or periodically In a reply that was published shortly completely or partly emerged - is to be after the death of J.M. Schopf, Gray and attributed to the also stout and solid stems Boucot (1979) stuck to their opinion and of Taeniocrada dubia K. et W., a rather stated that a number of features, to which enigmatic plant but occurring in association they now added recent biochemical data, with Prototaxites. suggest that Foerstia and Protosalvinia have On the basis of chemical analyses Niklas been land plants or, possibly, emergent (1976a) came to the conclusion that Proto• aquatics, neither fucoids nor algae but re• taxites loganii Dawson (the common Early presentatives of a separate group of land Devonian species) was either a land plant plants as previously advocated. or a water plant adapted to long periods With regard to Pro totaxites, this genus of drought. He isolated from the fossils was, apart from earlier attributions to seed a number of compounds considered in• plants, fungi or lichens, mostly attributed consistent with algal biochemistry. His either to Phaeophyta-Laminariales or to first conclusion is in accordance with a separate group of algae. But both the Jonker's deductions, the second one, how• land plant concept and the seaweed theory ever, is in direct contradiction to an attribu• have had supporters. The land plant theory tion to Rhodophytes. Also on the basis or a concept in the direction of semi• of organic chemical constituents Niklas aquatics gained the support of Dawson, (1976b) emphasized an algal affinity of Chiarugi, Lang, Arnold and Niklas. Sup• Pachytheca which is in accordance with porters of the seaweed theory have been, Jonker's view and might point to a deve• e.g. Carruthers, PenhalLow, Gothan and lopment of cystocarps under submerged Weyland and especially Krausel who argued conditions. that as marine algae of large dimensions When we evaluate the published indica• e~ist at present time, there is no need to tions of a terrestrial or of a partially JONKER-QUESTIONABLE ORIGIN OF EARLY LAND PLANTS 425 emerged nature, we may state that no value sea. One occurrence in Maine shows large is to be set upon: scattered stems in a coarse cobblestone cong• 1. the solid, firm cauloids, as large and lomerate on the slopes of Mt. Katahdin solid seaweeds even occur in modern times, with no trace of anything marine .... And I especially among Phaeophytes. It, how• will not have any reservations about accep• ever, opens the possibility for an adaptation ting an alliance of Prototaxites with the red to periods of drought; algae. I think the red algae got a big 2. the cuticularization, which term was lead on other kinds of plants during the used for the resistant nature of the outer Early Paleozoic and may have more or less surface and of the tetraspore wall. A completed their necessary environmental similar pseudo-cuticle and spore coat occur adaptations that time. We have had in many recent algae, Submerged Rhodo• "fucoids" in disrepute for some time but phyta- N emalionales included; the fact is that some of the forms deserve 3. conductive tubes, which occur in extant detailed study ". submerged Phaeophytes as well, and prob• My line of thought regarding the problem ably in a number of larger seaweeds of the rise of land life in the Early Devonian belonging to other algal groups. is as follows. An existent tendency (Jonker, With regard to the last item, some tubes 1976, 1977a, 1977b) in the plant life in Pro totaxites, and apparently in Foerstia to invade the land, was effective only after as well show annular thickening though no the atmospheric conditions made land life proof exists that these "tracheid-like tubes" possible, and could be effective only with were lignified. According to Schopf "they those plants that were firm and solid and can be of diverse significance and deriva• more or less resistant against desiccation. tion" and he doubted whether "they have This advantages those seaweeds that posses• anything to do with vascular protoxylem" sed an algal conductive system. The occur• as the internal organization is different rence of coenocytic or septate tubes alone, from that of vascular plants. Gray and either non-conducting or conductors of Boucot (1979), however, notwithstanding water or assimilates is, however, no proof of Schopf's arguments persist in their opinion life under terrestrial conditions. Hence we that the "Nematophytales" have been terres• may expect early land invading plants with trial and that the "tracheid-like cells" had, the larger Rhodophyta and Phaeophyta.

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