Description from Flora of China
Plenasium C. Presl.
Plants terrestrial, moderate-sized to large. Rhizome erect to shortly creeping, stout, woody, without scales. Fronds dimorphic or more commonly hemidimorphic with dimorphic pinnae; stipes arising as a crown at apex of rhizome, ± hairy when young, base of stipe swollen and with lateral flaplike stipules; lamina 1- or 2-pinnate, fertile portions reduced to a midrib with almost no lamina present; pinnae articulate to rachis. Sporangia large, naked, with a small patch annulus. 2n = 44.
About ten species, with some native hybrids; nearly worldwide in tropical and temperate regions, the greatest concentration of species in E and SE Asia; seven species including one putative hybrid species (one endemic) in China.