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Tmesipteris (family Psilotaceae) A genus of primitive cryptogamic vascular plants which (unlike Psilotum, the other genus of the family) have strap-shaped, pointed, one-veined leaves, and sporangia fused in pairs on to a pair of bracts. Like Psilotum, it has no roots, only rhizoids on its rhizomes. The genus is of great interest for its probable relationship to the most ancient vascular plants known, the Psilophytales of Devonian times, such as Rhynia and Hornea. There are probably only 2 species, confined to Australasia and some Pacific islands.