Psilotaceae

Abstract

Plants small to medium-sized, epiphytic or on rocks. Rhizomes creeping, brown, with protostele or siphonostele, bearing rhi-zoids; roots absent. Stems erect or pendulous, green, unbranched or dichotomously or pinnately branched; branches ridged to sulcate or complanate. Leaves small or rudimentary, with a single vein (microphylls) or lacking veins (enations), spirally or distichously alternate, sessile or subsessile, dimorphic; trophophylls scalelike and subulate-triangular, or lanceolate to narrowly ovate; sporophylls deeply bifid. Sporangia appearing solitary at or above bases of sporophylls, large, 2-or 3-lobed (sometimes interpreted as synangia of 2 or 3 unlobed sporangia), thick-walled, lacking an annulus, each lobe dehiscing longitudinally by a slit. Spores reniform, mono-lete, many (> 1000) per sporangium, exospore translucent, rugulate to foveolate. Gametophytes subterranean (Psilotum), non-photosynthetic, cylindrical, mycorrhizal. x = 52. Two genera (Psilotum, Tmesipteris) and ca. 17 species: tropics to temperate regions; one species in China. 松叶蕨属 song ye jue shu Plants small to medium-sized, often epiphytic. Rhizomes long creeping, mostly dichotomously branched. Stems erect to somewhat pendulous, glabrous, repeatedly dichotomously branched; branches green, ridged or complanate. Leaves reduced, veinless, ses-sile, dimorphic; trophophylls scalelike, subulate-triangular; sporophylls deeply bifid. Sporangia 3-lobed, attached at bases of sporo-phylls. Spores oblong in polar view, reniform in equatorial view, monolete, foveolate. Two species: widespread in tropical and warm-temperate regions; one species in China. Psilotum complanatum O. Swartz, which differs from P. nudum in its flattened stems 1.5-3 mm wide, has been reported from Malaysia and Oceania (among other regions). It eventually may be discovered in S China.