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Psilotaceae (order Psilotales) A family of very ancient and primitive vascular cryptogams (Pteridophyta), characterized by forked stems bearing small, scale-like appendages (Psilotum), or flattened leaves with a single vein (Tmesipteris), creeping rhizomes without roots, and spore capsules fused in pairs (Tmesipteris) or in triads (Psilotum). The gametophytes are cylindrical and subterranean, and live by means of a mycorrhizal fungus as saprophytes. There are 2 genera, and 4–8 species, the only living representatives of the order, probably the most primitive of living vascular plants, and possibly related to the Devonian fossil group the Psilophytales. Tmesipteris is confined to the Australasian region.