Phylloglossum, a genus in the clubmoss family Lycopodiaceae, is a small plant superficially resembling a tiny grass plant, growing with a rosette of slender leaves 2–5 cm long from an underground bulb-like root.

It has a single central stem up to 5 cm tall bearing a spore-producing cone at the apex, and was previously classified variously in the family Lycopodiaceae or in its own family the Phylloglossaceae, but recent genetic evidence demonstrates it is most closely related to the genus Huperzia and is a sister clade to the genus Phlegmariurus, which was formerly included in Huperzia.

[2] A morphological character that complicates this is the presence of a perenniating tuber in Phylloglossum, which has, in the past, misled scientists to place it more closely to the genus Lycopodiella.

Phylloglossum is unique within Lycopodiaceae due to this underground perenniating tuber, which is a reduced stem system that has developed to be considered a new organ.

[3][4] Its gametophyte is non-photosynthetic at first, getting its nutrients from mycorrhiza, but develops a photosynthetic crown as it matures.