Aerial shoots to 50 cm, 4 mm diam. at base. Appendages 0.7--2.5 mm (sterile), 1--1.5 mm (fertile). Synangia yellowish to greenish yellow, 2--3 mm wide. Low to mesic woods, thickets, swamps, hammocks, rocky slopes; 0--50 m (1100 m in Ariz.); Ala., Ariz., Fla., Ga., La., Miss., S.C., Tex.; Mexico; West Indies in the Antilles; Central America; South America; tropical Asia; tropical Africa. Reports of Psilotum nudum in New Mexico and in west Texas remain unverified. A wide range of chromosome numbers on material outside the flora has been reported for this species: n =ca.46--56, 104, 210. Most counts, however, are based on n =52 (reviewed in P.J. Brownsey and J.D. Lovis 1987). No count is available from North American material. Psilotum nudum occurs as a minor weed in greenhouses. Many horticultural forms---including one without appendages and with terminal synangia (A.S. Rouffa 1971)---are grown, especially in Japan.