Lycopodiaceae P.Beauv. ex Mirb.

Terrestrial, epilithic or epiphytic. Sporophytes emergent, photosynthetic, annually deciduous or perennially evergreen and long-lived. Protostelic (mostly), plectostelic (in lateral shoots of some species) or solenstelic (rarely). Habit varied, including: (i) solitary unbranched determinate shoots arising from a subterranean tuber bearing the roots; (ii) tufted isotomous indeterminate shoots arising from the axils of basal leaves, with roots arising from the narrow stem stele and descending through the broad cortex to the stem base to emerge as a basal tuft in Huperzioideae; and (iii) non-tufted, anisotomous shoots with indeterminate horizontal stems and determinate aerial stems usually of differing thickness and branching pattern, with roots arising from a broad stem stele and emerging directly through the stem wall in Lycopodioideae and Lycopodielloideae. Shoots may be erect, pendulous, scrambling or climbing. Shoots homophyllous with undifferentiated sterile leaves and sporophylls, or heterophyllous with markedly differentiated sterile leaves and sporophylls. Sterile leaves simple and single-veined, isophyllous or anisophyllous, lacking a ligule, arranged in alternating subspiral whorls of 2–11, appearing subopposite decussate, longitudinally ranked, verticillate or spiralling. Sporophylls intermingled with undifferentiated sterile leaves or arranged into sessile or leafless pedunculate terminal or lateral spikes. Sporophylls simple and single-veined, isophyllous, lacking a ligule, persisting after sporangia dehiscence or deciduous after sporangia dehiscence. Sporophyll arrangement similar to sterile leaves or with a reduced number of parts per subspiral whorl in heterophyllous species. Sporangia axillary, reniform to globular, isovalvate or anisovalvate. Spores trilete tetrahedral (sometimes appearing round) with bacculate, fovelate, fossulate, reticulate, rugate or scabrate surface ornamentation. Gametophytes subterranean and mycoheterotrophic or emergent and photosynthetic, tuberous of various forms, with gametangia on the upper surface.

The habit and habitat of Lycopodiaceae is extremely diverse, including a myriad of terrestrial, epilithic and epiphytic forms ranging from colonial terrestrial plants in oligotrophic wetlands to hanging epiphytes in rainforest canopies. They occur in a variety of high light humid habitats and are generally absent from deep shade or arid zones. Most species diversity globally is associated with montane areas, especially in the tropics.

Many species of the epiphytic genus Phlegmariurus (tassel ferns) are cultivated as ornamental hanging basket plants, especially in tropical and subtropical regions (see Jones 1987; Elliot & Jones 1993; Spencer 1995; McAuliffe 2012 under the generic names Lycopodium L. and Huperzia Bernh.). The trade in tassel ferns has been regulated in Queensland to prevent poaching of wild plants, with native species being required to be produced artificially and tagged by approved propagators (Anon. 2010). Huperzine extracted from Huperzia serrata (Toothed Clubmoss) has been used as a traditional medicine in China and has been reported to have efficacy in preventing Alzheimer's disease (Ma & Gang 2008). Several Australian species of the genera Huperzia and Phlegmariurus contain Huperzine, but are not presently used as a commercial source of Huperzine (Goodger et al. 2008; Lim et al. 2010). Several species of Phlegmariurus (tassel ferns) are named by, and have cultural significance for, indigenous people of the Wet Tropics, Queensland.