Selaginella hansenii
Selaginella underwoodii
Hansen's spike-moss
Underwood's spike-moss
not readily fragmenting, prostrate, upperside and underside structurally different, irregularly forked, branches determinate, tips upturned.
radially symmetric, long-creeping, short-creeping, or pendent, not readily fragmenting, irregularly forked, without budlike arrested branches, tips straight;
main stem indeterminate, lateral branches determinate, spreading, 1–2-forked.
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).
monomorphic, in alternate pseudowhorls of 4 (on main stem and older lateral branches) or 3 (on young lateral branches and secondary branches), loosely appressed, ascending, green, linear to linear-lanceolate or narrowly triangular-lanceolate, (2–)2.5–3.4 × 0.45–0.5(–0.7) mm;
abaxial ridges prominent;
base mostly cuneate and decurrent, rarely rounded and adnate (on young branches), pubescent or glabrous;
margins entire to denticulate or very short-ciliate, cilia transparent, scattered, mostly ascending, dentiform toward apex, 0.02–0.07 mm;
apex keeled, slightly attenuate, short- to long-bristled;
bristle transparent greenish to greenish-yellowish, rarely white, smooth, seldom slightly puberulent, sometimes breaking off, 0.25–0.7(–1) mm.
solitary, 5–7 mm;
sporophylls ovate-deltate to ovate-triangular, abaxial ridges not prominent, base glabrous, margins short-ciliate, apex bristled.
sometimes paired, 0.5–3.5 cm;
sporophylls lanceolate to ovate-lanceolate, abaxial ridges prominent, base glabrous, with prominent auricles (no other species has such prominent auricles), margins entire or very short-ciliate to denticulate, apex keeled, short- to long-bristled.
borne on upperside of stems, throughout stem length, 0.25–0.45 mm diam.
borne on upperside of stems, throughout stem length, 0.15–0.27(–0.3) mm diam.
Selaginella hansenii
Selaginella underwoodii
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.)
R. M. Tryon (1971) reported that the bristle on Selaginella underwoodii leaves is longer (to 1.44 mm) in the southern part of the range and shorter (to 0.43 mm) northward and in central Arizona. Selaginella underwoodii seems to be closely related to S. oregana, perhaps sharing a common ancestor.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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