Selaginellaceae

Abstract

Terrestrial, or very occasionally epiphytic, usually perennial plants, of varied habit, with an erect or prostrate main stem and subsidiary branch systems of varying arrangements, the basal portions not differentiated into a distinct rhizome although some erect species spread by means of creeping basal branches known as sobols, which in turn give rise to further erect branches; growing points not protected by scales. Roots (sometimes termed rhizophores) dichotomously branched, varying in thickness, arising from the axils of branches, either throughout the length of the main stem, or basally (acting as support in erect species), or occasionally apparently adventitiously. Main stems either far-creeping and often much-branched, of indefinite growth which may be only seasonally halted or terminated; or short-creeping and then becoming erect, often with a distinct unbranched (‘caulescent’) region below, and with variously arranged frond-like complanate branch systems (pseudofronds) of finite growth above, further growth arising only from basal branches; sometimes exhibiting a scrambling or climbing habit. Leaves spirally arranged, ligulate, those on basal creeping portions often distantly arranged, either all similar or of two kinds, at least on the secondary and ultimate branches where they are arranged in four ranks. Strobili terminal on primary or ultimate branches, compact, or occasionally more spread out along secondary branches, apex occasionally reverting to become a vegetative shoot; or, more rarely, in a lateral position on a primary or secondary branch. Sporophylls leaf-like, spirally arranged or in ranks of four, uniform or, more rarely, dimorphic, subtending sporangia which are on the adaxial surface just above the ligule; sporangia stalked, of two kinds, variously disposed throughout the strobilus, megasporangia assuming a shape dictated by the developing megaspores, microsporangia globose or slightly wider than long, thin-walled but with areas of thickened cells which aid dehiscence; megaspores trilete, usually four (> 42 have been observed) in each sporangium, pale buff or white, with distinct muri or ridges around the equator and along the triradiate scar, sporoderm variously patterned, rugose-reticulate, rugose, papillate, tuberculate, granulate, rarely plain on proximal face, rugose-reticulate patterns predominate generally there is less ornamentation on the proximal face than on the distal face, 200–600, μm in equatorial diam.; microspores trilete, > 100 in each sporangium, ranging in colour from yellow, through orange-brown, to red, sporoderm variously patterned from finely echinulate through papillate to verrucate, sometimes strongly rugose, 20–60 μm in diam.