Description from Flora of China
Plants terrestrial, helophytic, or epiphytic, small to large. Main stems creeping, pendulous, climbing, or short and erect, mainly protostelic, rarely actinostelic or plectostelic, on substrate surface or subterranean, or forming stolons. Upright shoots once to multiple times dichotomously branched, conspicuously leafy; upper portion of stem and branchlets with or without bulbils. Lateral branches ascending or erect, dichotomously branched or nearly sympodially branched, rarely pseudomonopodially branched. Main stems and lateral branches rounded or flat in cross section. Leaves as microphylls, with 1 unbranched midrib, monomorphic, spirally arranged. Leaves on subterranean parts flat, appressed, not photosynthetic, and scalelike; leaves on aerial parts appressed, ascending or spreading, subulate, linear, lanceolate, ovate, or scalelike, not lustrous or lustrous, remote to dense and imbricate, papery, leathery, or thinly leathery, base truncate, margin entire or serrate. Strobili terminal on branchlets or main stem, abruptly becoming much smaller than or similar to sterile branches or branchlets in size, solitary, erect, nodding, or pendent, terete, sessile or stalked. Sporophylls homomorphic with or different from trophophylls, monomorphic or dimorphic, papery, margin toothed, membranous. Sporangia in axils of sporophylls, yellow, reniform, thick-walled, outer walls variously modified. Spores trilete, thick-walled, surfaces pitted to small-grooved, rugulose, or reticulate. Gametophytes subterranean or surficial. x = 11, 13, 17, 23.
Some pteridologists recognize a narrowly defined Lycopodiaceae s.s. and Huperziaceae with the latter comprising Huperzia, Phlegmariurus, and Phylloglossum Kunze, considering that the split between Huperziaceae and Lycopodiaceae s.s. has been dated to ca. 350 million years ago using plastid rbcL data (Wikström & Kenrick, Molec. Phylogen. Evol. 19: 177-186. 2001), an age much older than many extant fern families/orders. In spite of this, here Lycopodiaceae s.l. including Huperziaceae is recognized because of the sister relationship between Huperziaceae and Lycopodiaceae s.s.
In the Lycopodiaceae, sometimes Lycopodiastrum is subsumed under Lycopodium. However, the split between Lycopodiastrum and Lycopodium s.s. has been dated to the Permian Period (251-299 million years ago), much earlier than when extant species of Lycopodium s.s. started to diversify (Wikström & Kenrick, loc. cit.). Also, the morphology of Lycopodiastrum is distinct from Lycopodium. Therefore, Lycopodiastrum is recognized here.
Zhang Libing. 2004. Huperziaceae and Lycopodiaceae. In: Zhang Xianchun, ed., Fl. Reipubl. Popularis Sin. 6(3): 1-85.
Five genera and 360-400 species: cosmopolitan, with centers of diversity in the tropics; five genera and 66 species (28 endemic) in China.
(Authors: Zhang Libing (张丽兵); Kunio Iwatsuki)