LY'COPODIAMES (Neo-Lat. nom. pl., from \titan, lykos, wolf + irons, pans, foot: so called from the appearance of the roots). One of the three great divisions of fern-plants (pterido phytes), and usually regarded as the one of high est rank. Popularly they are called 'elub-mosses.' and the majority of them belong to two genera, Lyeopodium and Selaginella. They differ strik ingly in habit from the other pteridophytes, in that the aerial body consists of slender branch ing stems thickly clothed with very numerous small leaves. Many of the more delicate species of Selaginella resemble coarse mosses, and are common in greenhouses as decorative plants. In the Carboniferous period (enal measures) the club-mosses included tree forms, some of which were very bulky and formed a conspicuous part of the forest vegetation. Only the smaller forms have survived, about five hundred species hieing represented in the flora of to-day. In temperate and colder regions the coarser Lycopodiums pre vail, often called 'ground-pines' as well as 'club mosses': while in the tropics the more delicate and more numerous Selaginellas are chiefly dis played. Aside from the moss-like habit. the most conspicuous feature of the group is the `strobilus.' The word literally means 'cone,' and refers to a terminal, conical or cylindrical, spo•e-bearing structure. It is the presence of these club-like bodies at the ends of the moss-like branches which has suggested the name 'elub-mosses.' The strobilus is composed of a series of closely over lapping bracts (reduced leaves), each one of which bears at its base upon the. upper side a single spore-ease (sporangium), in which the spores are produced. This strobilus is the same structure as that called a 'cone' in the pines and their allies.
A very important fact in connection with the club-mosses is that the species of Selaginella are heterosporous. When a microspore germinates it produces a very small male plant (male gameto phyte), so small that it does not escape from the spore. This small and concealed male plant de velops a sex-organ (antheridium) which pro duces sperms. The sperms of elub-mosses differ from those of other pteridophytes in that they are very small and have only two cilia for locomo tion. When a megaspore germinates it produces
a small female plant (female gametophyte), which remains within the megaspore, but rup tures it on one side, growing out a little beyond it. In this exposed part of the little female plant sex-organs (arehegonia) are developed, in each of which an egg is formed. To these eggs the sperms have access and fertilize them. The resulting fertilized egg (onspore) then germi nates and produces the ordinary leafy club-moss,. which is a sexless plant (sporophyto. The habit of some species of Selaginella which do not shed the megaspore is so suggestive of seed-plants that many think the seed-plants, or at least. some of them, may have been derived from the elub mosses.
The quillworts (species of Isoetes) should probably be associated with the elub-mosses in the group Lyeopodiales, though some would in clude them with the true ferns (Filieales). They look like very slender tufted grasses growing in water, the habit being very unlike that of the dub mosses. In many important particulars, how ever, the resemblance is striking, the most conspicuous being the single spore-case (spo rangium) at the base of each spore-bearing leaf. Quillwo•ts are also heterosporous, as are the species of Selaginella. The most important dif ference is in the sperm, which is large and bears many cilia, as in the ordinary ferns.
Recently it has been thought that perhaps the adder-tongues (Ophioglossum) and nmonworts (Botryehium) should be placed among the Lyeo rather than with the true ferns, with which they have always been associated, although as a very distinct group.
The genus Lyeopodium has fossil representa tives, called Lyeopodites, in the Devonian. Car boniferous. and Jurassic rocks. Allied forms are Psilotum and Psilophyton, the latter of which is very abundant in the form of graceful leafy terminal branches in the Devonian shales and sandstones of North America and the [nine provinces of Germany. Other fossils, usually eon sidered to be gigantic ancestral club-mosses, are the lepidodendrids of late Pa]eozoie time. See the articles LEetuonExpitox: PrEarnornviTs; ALTERNAT1O OF GENERATIONS; 06SPOttE; SPER