Plants small, terrestrial, epipetric, or, rarely, epiphytic. Rhizomes prostrate, decumbent, or erect, creeping, slender, leafy, producing roots (rhizophores) at bases or intermittently on creeping rhizomes. Stems prostrate or erect, branching repeatedly. Sterile leaves (trophophylls) all alike, arranged spirally, small, simple, circular to linear, with a single vein, or of 2 kinds and arranged in 4 ranks (2 lateral and spreading; 2 medial, appressed, and ascending), small Iigules present at abaxial bases. Strobili on terminal branches and tips, 1-2.5 mm wide, composed of fertile leaves (sporophylls) different from sterile leaves (except in Selaginella deflexa, which has cylindrical cones, 4-6 mm wide). Sporangia of 2 kinds, borne at adaxial bases of sporophylls; thousands of microspores (20-60 J.liil diam.) in ovoid to reniform microsporangia, and 4 megaspores (200-600 J.liil diam.) in 4-Iobed sporangia, borne in separate sporangia but on same strobilus.

The only genus (sometimes divided into five subgenera) in the family Selaginellaceae, Selaginella includes about 750 species worldwide, most commonly in tropical and subtropical regions. Represented in Hawai 'i by two endemic and three naturalized species. The distinctive and very different Selaginella deflexa belongs to the subgenus Selaginella, and the other four species belong to subgenus Stachygynandrum (P. Beauv.) Baket:

Because characters separating the species of Selaginella are often subtle and species are difficult to distinguish, new native species may be found, and unrecognized horticultural taxa that may already be naturalized may be discovered.

KEY TO THE NATIVE AND NATURALIZED SELAGINELLA SPECIES IN HAWAI'I

1. Sterile leaves all alike, spirally arranged; aerial stems simple, unbranched, round; strobili resembling sterile shoots but about twice as thick; all major islands except Lana 'i ........ : . . . . . . . . . . . . . . . . . . . . . . . 2. S. deflexa

1. Sterile leaves of 2 kinds in 4 rows, 2 lateral, spreading, and 2 medial, appressed on the stems; aerial stems branched, flattened; strobili differing from sterile stems, narrower; O'ahu, Maui, Hawai'i, or all major islands (2).

2(1). Stems prostrate, long-creeping, repeatedly branched, lateral branches ascending, these in tum 1- to 3-branched; rhizophores borne all along length of main stem; O'ahu, Maui, Hawai 'i ........................ 3. S. kraussiana

2. Stems ascending or erect from decumbent base, unbranched in lower half; rhizophores confined to bases of main stems, or short and borne along lower 1/3 of main stems (3).

3(2). Main stems with swollen joints scattered along their length; rhizophores borne along lower 1/3 of main stems, up to 15 em long, 0.5-1 mm in diam.; Hawai 'i .......................................... 4. S. stellata

3. Main stems without swollen joints; rhizophores at very bases of main stems (rarely along the lower 114), less than 3 cm long, 0.2 mm or less in diam. (4).

4(3). Stems straw-colored, branching near bases; rhizophores arising from stems; all major islands ....................................... 1. S. arbuscula

4. Stems red, 8-25 cm long before branching; rhizophores mostly arising from stolons; Hawai'i ........................................ 5. S. umbrosa