Selaginella hansenii
Selaginella arenicola
Hansen's spike-moss
sand spike-moss
not readily fragmenting, prostrate, upperside and underside structurally different, irregularly forked, branches determinate, tips upturned.
radially symmetric, underground (rhizomatous) and aerial, not readily fragmenting, irregularly forked; rhizomatous and aerial stems often with 1 branch arrested, budlike, tips straight; rhizomatous stems mostly ascending;
aerial stems erect or ascending.
with underside leaves slightly longer and narrower than upperside leaves, otherwise monomorphic, not clearly ranked, tightly appressed, ascending, green or green with red spots, or reddish, linear-lanceolate (underside) to linear-triangular (upperside), (2–)3–4.5 × 0.5–0.6 mm;
abaxial ridges present;
base abruptly adnate, pubescent (sometimes glabrous);
margins ciliate, cilia white to white opaque, strongly appressed and ascending, 0.03–0.1 mm;
apex with bristle white to white-opaque, 0.5–1.4 mm (those on underside leaves sometimes 1/4–1/2 longer than those on upperside leaves).
dimorphic, in pseudowhorls of 4.
solitary, 5–7 mm;
sporophylls ovate-deltate to ovate-triangular, abaxial ridges not prominent, base glabrous, margins short-ciliate, apex bristled.
solitary, (0.5–)1–3(–3.5) cm;
sporophylls ovate-lanceolate to lanceolate, often abruptly tapering toward apex, abaxial ridges not prominent, base glabrous, rarely with few hairs, margins ciliate, apex often recurved, bristled.
borne on upperside of stems, throughout stem length, 0.25–0.45 mm diam.
borne on upperside of stems, restricted to rhizomatous stems, 0.2–0.33 mm diam.
stem leaves persistent, appressed, scalelike.
stem leaves tightly or somewhat loosely appressed, ascending, green, narrowly triangular-lanceolate or narrowly lanceolate, 2–3 × 0.4–0.5 mm;
abaxial ridges present;
base cuneate, strongly decurrent, pubescent or glabrescent;
hairs restricted to base;
margins short-ciliate, cilia transparent, scattered, spreading at base, dentiform and ascending toward apex, 0.02–0.07 mm;
apex plane, attenuate;
bristle white to whitish, straight, coarsely puberulent, 0.25–0.85(–0.9) mm.
Selaginella hansenii
Selaginella arenicola
Leaf dimorphism in Selaginella hansenii is only slightly and inconsistently expressed; the upperside leaves tend to be more lanceolate, short, and slightly thick, whereas the underside leaves tend to be more linear, longer, and thinner, but in some specimens the leaves are monomorphic. Red leaves are rare within Selaginella subg. Tetragonostachys, otherwise found in the flora only occasionally in S. rupestris. Such leaves are more common in S. steyermarkii Alston from southern Mexico and Guatemala and S. sartorii Hieronymus from Mexico.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Selaginella arenicola and related species have been considered as forming a species complex. This interpretation has been the center of much taxonomic controversy (R. M. Tryon 1955; G. P. Van Eseltine 1918). Tryon recognized one species in the complex, S. arenicola, with three subspecies: subsp. arenicola, subsp. riddellii, and subsp. acanthonata. Other authors (e.g., R. T. Clausen 1946) treated the subspecies as species. I recognize two well-defined species within this complex, S. arenicola and S. acanthonota, which are readily distinguishable by the characteristics given in the key. Some specimens reported by R. M. Tryon (1955) as intermediate between S. arenicola and S. acanthonota appear to be hybrids between S. acanthonota and S. rupestris. In particular, more detailed studies are needed to assess whether populations from Georgia are hybrids or variants of S. acanthonota or of S. rupestris. Future studies are also needed to determine relationships and proper taxonomic rank of Selaginella arenicola subsp. arenicola and subsp. riddellii, which are provisionally recognized here.
Subspecies 2.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Leaves mostly tightly appressed; base conspicuously pubescent; strobili distinctly larger in diameter than subtending stem; sporophyll apex often recurved. | subsp. arenicola |
1. Leaves usually loosely appressed; base very often glabrescent; strobili not distinctly larger in diameter than subtending stem; sporophyll apex usually straight. | subsp. riddellii |
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