Watson's Spikemoss

R. M. Tryon (1955) suggested that Selaginella watsonii is a possible ancestor of (or shares a common ancestor with) S . leucobryoides , S . asprella , and S . utahensis (see discussion).

Plants on rock or terrestrial, forming long or compact cushionlike mats. Stems radially symmetric, decumbent to long-creeping, not readily fragmenting, irregularly forked, without budlike arrested branches, tips straight; main stem conspicuously determinate, lateral branches conspicuously or inconspicuously determinate, strongly ascending, 1--3-forked. Rhizophores borne on upperside of stems, throughout stem length, 0.35--0.55 mm diam. Leaves monomorphic, in alternate pseudowhorls of 4, tightly or loosely appressed, ascending, green, linear-lanceolate, (2.5--)3--4 X 0.5--0.7 mm; abaxial ridges prominent; base cuneate, decurrent, glabrous or sometimes pubescent; margins entire or short-ciliate, cilia transparent, scattered, spreading, 0.05--0.1 mm; apex strongly keeled, obtuse, abruptly bristled; bristle whitish to transparent, smooth, 0.25--0.5 mm. Strobili solitary, 0.5--3(--3.5) cm; sporophylls lanceolate to ovate-lanceolate, abaxial ridges well defined, base glabrous, margins entire, rarely dentate, apex strongly keeled to truncate in profile, short-bristled.

Ariz., Calif., Idaho, Mont., Nev., Oreg., Utah, Wyo.

On exposed or shaded cliffs, rocky slopes, rock crevices, granite boulders, quartzite rock, gravelly or sandy soil, alpine meadows, or swampy grounds; 1800--4300m.

Selaginella watsonii is a species of spikemoss known by the common name Watson's spikemoss. It is native to the western United States, where it grows in many rocky habitat types, including high mountain peaks in alpine climates. This lycophyte forms mats or cushions of short, forking stems. They are lined with linear or lance-shaped leaves no more than 4 millimeters long, often tipped with tiny bristles. The strobili containing the reproductive structures are 1 to 3 centimeters long.