Selaginella siamensis

Plants terrestrial, evergreen or seasonally green, long creeping or ascending from decumbent base or scandent, 20-45 cm. Rhizophores at intervals throughout length of main stem or up to middle of main stem, borne on ventral side in axils of branches. Main stems branched throughout, anisotomously branched, brown, 1-2 mm in diam. in lower part, terete, glabrous, branches few to many, some primary lateral branches developing into long branch systems, twice pinnately branched, tertiary branches forked, branchlets sparse and regular, adjacent primary branches on main stem 2-8 cm apart; leafy portion of main stem including leaves 3-3.5 mm wide at middle, ultimate branches 2-4 mm wide including leaves. Leaves papery, not iridescent, not white-margined, margin not entire or subentire; leaves on main stems approximate or sparse, larger than those on branches, slightly dimorphic, green or yellowish, oblong-ovate, appressed, not keeled, base not peltate, margin ciliolate. Axillary leaves on main stems obviously larger than those on branches, oblong-elliptic or oblong-ovate, base obtuse or subcordate; axillary leaves on branches symmetrical, ovate, 1.3-2.5 × 0.7-1.7 mm, base exauriculate, margin ciliolate. Dorsal leaves asymmetrical or ± symmetrical, those on main stems obviously larger than those on branches, base obliquely cordate or biauriculate, margin ciliolate, apex aristate (1/3-1/2 as long as leaves); dorsal leaves on branches imbricate, ovate-elliptic or ovate-orbicular, 1.2-1.8 × 0.4-0.8 mm, base obliquely subcordate, margin entire or subentire, apex aristate, parallel to axis, arista ca. 1/3 as long as leaves. Ventral leaves asymmetrical, those on main stem obviously larger than those on branches, basiscopic margin ciliolate; ventral leaves on branches contiguous, slightly ascending, ovate or oblong-ovate, 1.8-2.6 × 0.8-1.4 mm, margin ciliolate, apex acute and aristate; acroscopic base rounded, overlapping stem and branches; ventral leaves on ultimate branches with basiscopic base rounded, margin subentire, shortly ciliolate at base. Strobili solitary, terminal, compact, tetragonal, 4-10 × 1.2-2.6 mm; sporophylls uniform, not white-margined, ovate-triangular, carinate, margin minutely ciliolate, apex acuminate; megasporophylls in basal portion on lower side or megasporophylls and microsporophylls at intervals, or only 1 megasporophyll at base of lower side of strobilus, elsewhere with microsporophylls; microsporangia cordate, relatively thick, marginal cells differentiated, smaller with thin walls; microspores yellowish orange, megaspores brown.