Scientific name: Lycopodiaceae
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Vietnamese name: Thông đất
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The Lycopodiaceae are terrestrial or epiphytic homosporous, protostelic vascular plants comprising about half a dozen genera and 300 species. The free-living sporophytic plant body is basically dichotomously branching, consisting of a rhizome with adventitious roots, and an aerial portion with numerous, closely spaced, mostly spirally disposed microphyllous leaves, each with a single vascular trace. Eusporagia are found on the upper surface of the microphylls, either in unmodified shoot axes or in compact strobili. The independent gametophytes are bisexual, and are either irregularly lobed photosynthetic masses, or subterranean, branching structures that lack chlorophyll and require a fungal symbiont. Multiflagellated sperm produced in an antheridium must travel through a film of water to reach the egg of an archegonium in order to initiate the zygote that may develop into the new sporophyte individual.

The Lycopodiaceae (class Lycopodiopsida, order Lycopodiales) are a family of vascular plants, including all of the core clubmosses. These plants bear spores on specialized structures at the apex of a shoot; they resemble a tiny battle club, from which the common name derives. They are non-flowering and do not produce seeds.

The genera Huperzia, Phlegmariurus and Phylloglossum, the species of which were generally included in a more broadly defined Lycopodium in older classifications, are treated in the separate family Huperziaceae in some classifications, and are treated so here; they differ in producing spores in small lateral structures in the leaf axils. There is as yet no consensus on the recognition of Huperziaceae as a separate family; a more broadly defined Lycopodiaceae, including these genera, is still recognized in some classifications.

The species within this family generally have chromosome counts of n=34. A notable exception are the species in genus Diphasiastrum, which have counts of n=23.