In this article we will discuss about the characters of Lepidocarpon.
Though Lepidocarpon is known only from its strobilus it has been widely held that it could have been borne on a Lepidophlois type of stem. The fossils of Lepidocarpon have been obtained from the coal strata in England and U.S.A.
The strobili were mososporangiate though the plant was heterosporous. The microsporophyll’s were like those of Lepidostrobus. Each microsporophyll was peltate and had an elongate microsporangium. The megasporophylls bore elongate microsporangia on their adaxial surface.
The jacket of the mega-sporangium extended at the apex to form a projection. The sporangium was enveloped by the flaps of a tissue which is termed as integument (Fig.57). But it is doubtful how far this terminology is appropriate. Because in reality this inegument is nothing but an upturning of the megasporophyll though many people believe it to be a special outgrowth artising from the megasporophyll.
There were four spores in a sporangium of which only one developed into the female gametophyte. The size of the gametophyte and the fact as to whether it completely or incompletely filled the sporangium are specific characters. Andrews and Pannel (1941) have reported several fertile mega-gametophytes with archegonia at the apex.
The mega-sporangial cavity also showed many spores of which at least some of them were the microspores of Lepidocarpon. This suggests that Lepidocarpon had something like an incipient pollination which is also seen in the extant genus Selaginella.
The one unique feature of Lepidocarpon which is not seen in any lycopods extinct or extant was the permanent retention of the mega-gametophyte within the sporangium thus marking a significant step towards the evolution of seed habit.
The megasporophylls were, ultimately liberated and on falling upon a suitable substratum the embryo developed into the sporophyte. It will be very interesting to analyse whether Lepidocarpon could be regarded as having attained a seed habit.
Most of the attributes of Lepidocarpon – an integument, a permanent retention of the female gametophyte, development of only one spore in the mega-sporangium, incipient pollination, all point out towards the seed like habit.
But a closer scrutiny reveals that all the seed like features are only superficial, for, the so called integument is a part of the megasporophyll and not of the mega-sporangium. Further there is no formation of pollen tube, no seed coat and in all probability the embryo did not have dormancy characteristic of true spermatophytes.
All these clearly show that though Lepidocarpaceae apparently possessed the attributes of a seed-habit (particularly in the permanent retention of the female gametophyte but the additional features to support such a retention were not sufficient) it did not reach the level of a seed habit and hence it could at best be regarded as a pseudo-spermatophyte.