Latin umbrosus, shady or growing in shade, in reference to the habitat of this species.

Plants terrestrial. Stems erect, arising from short, decumbent bases, 8-25(-40) cm long before branching, not clustered, red, 1/3 to 2/3 frond length, stoloniferous, stem leaves all similar, appressed; branched portion blade-like, forming a closed, deltate to deltate-ovate, fanlike pattern, 10-25 x 10-25 cm, green, often tilted at a 45-90° angle from the stem; rhizophores confined to bases of main stems, to 4 cm long, hairlike; sterile lateral leaves ovate-falcate, main stem leaves usually uniform, 2.5-4 x 0.75-2 mm, lower margins entire, acroscopic margins ciliate, tips pointed; median leaves lanceolate to ovate-lanceolate, smaller, 1-3 x 0.25-1.5 mm; margins entire to serrate, tips acute; fertile leaves monomorphic, narrowly ovate, about 1 mm long, keeled, with acute tips; strobili terminal on branches, 1-2.5 cm long.

Found growing naturalized in 'Akaka Falls State Park on Hawai 'i Island in 2000. In 1994 it was seen growing as a cultivated plant in the Hawai 'i Tropical Botanical Garden north of Hilo. Selaginella umbrosa spreads by proliferations off the stolons. Its current distribution in Hawai 'i is not known, but it is likely to spread. Native from the Yucatan to Colombia and Venezuela. Also found in Barbados and Tobago but probably naturalized there.

Selaginella umbrosa may be distinguished by its red, stipelike stems and a triangular, fan-shaped, bladelike branching portion of the stem that inclines at a 45-90° angle from the stem (in live plants).