Selaginella apoda
Selaginella rupestris
meadow spike-moss, sélaginelle apode
dwarf spike-moss, ledge spikemoss, northern selaginella, rock selaginella, rock spike-moss, sélaginelle des rochers, sélaginelle rupestre
prostrate to short-creeping, sparsely branched, branches mostly simple or 1-forked, flat, not articulate, glabrous.
radially symmetric, long to moderately short-creeping to decumbent, not readily fragmenting, irregularly forked, without budlike arrested branches, tips straight;
main stem indeterminate, lateral branches conspicuously or inconspicuously determinate, sometimes ascending, 1–3-forked.
delicate, papery.
monomorphic, in alternate pseudowhorls of 6 (on main stem) to 4 (on lateral branches), tightly appressed, ascending, green, occasionally reddish, linear or linear-lanceolate, 2.5–4(–4.5) X 0.45–0.6 mm;
abaxial ridges well defined;
base cuneate and decurrent on underside to rounded and adnate on upperside, pubescent or glabrous;
margins long-ciliate, cilia transparent, spreading, (0.05–)0.07–0.17 mm;
apex slightly keeled, mostly attenuate;
bristle white, whitish, or transparent, puberulent, 0.45–1(–1.5) mm.
paired or solitary, lax, flattened, 1–2 cm;
sporophylls ovate to ovate-deltate, strongly keeled, keel dentate, base slightly cordate to rounded, margins with scattered teeth, apex acuminate;
megasporophylls larger and wider than microsporophylls, usually on underside of strobili.
solitary, 0.5–3.5 cm;
sporophylls deltate-ovate to ovate-lanceolate, strongly tapering or not toward apex, abaxial ridges well defined, base glabrous, margins ciliate to slightly dentate, apex slightly keeled, not truncate in profile, long-bristled.
axillary, throughout stem length or restricted to proximal 1/3 of stem, 0.05–0.1 mm diam.
borne on upperside of stems, throughout stem length, 0.25–0.45 mm diam.
leaves distant, green, ovate to ovate-lanceolate, 1.35–2.25 × 0.75–1.35 mm;
base slightly cordate;
margins green or with 1 row of transparent cells, serrate;
apex acute, ending in teeth.
leaves ovate-lanceolate, 1–1.6 × 0.45–0.7 mm;
base oblique on inner side, rounded and prominent on outer side;
margins green or with row of transparent cells, serrate;
apex straight, acuminate to long-acuminate.
= 18.
Selaginella apoda
Selaginella rupestris
Selaginella apoda is the central component of a taxonomically difficult species complex of eastern North America. It is closely related to S. eclipes (see discussion) and S. ludoviciana. Naturally occurring and experimental hybrids between S. apoda and S. ludoviciana have been reported (P. Somers and W. R. Buck 1975; T. R. Webster 1990). Also, some evidence indicates that hybrids may occur between S. apoda and S. eclipes. More studies are needed in this complex.
The species in the S. apoda complex may be best classified under subg. Homostachys of J. G. Baker (1883, 1887), with which they share flattened strobili and larger sporophylls (megasporophylls) that are usually in the same plane as the vegetative lateral leaves. They are, however, treated here with the other heterophyllous species of subg. Stachygynandrum until a reassessment of the classification of the genus Selaginella can be made.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Selaginella rupestris has the widest range of any selaginella in the flora. It is variable in many characteristics, e.g., the hairiness of the margins (which sometimes are not hairy), leaf base pubescence, and shape of sporophylls. The variation in sporangial distribution pattern in the strobili and the number of megaspores per megasporangium are important for understanding reproduction and relationships in this species. Very often the strobili are wholly megasporangiate, with only 1–2 megaspores per megasporangium, suggesting asexual reproduction. In other cases, both types of sporangia are present in a strobilus, suggesting sexual reproduction. R. M. Tryon (1971) correlated sporangial and spore distribution patterns in S. rupestris with distributional ranges and concluded that there are four races. Race A has 4 megaspores per megasporangium, has microsporangia, is sexual, and is distributed from southeastern Pennsylvania south to Georgia and Alabama. Race B has 1–2(–4) megaspores per megasporangium, has microsporangia, has an unknown type of reproduction, and has the same range as Race A, but it extends into New York. Race C has 1–2 megaspores per megasporangium, has microsporangia, is probably asexual, and is distributed throughout the species range. Race D has 1–2 megaspores per megasporangium, lacks microsporangia, is therefore asexual, and is found throughout the species range except where Race A occurs. These patterns suggest the presence of more than one species within S. rupestris in the broad sense. More studies, especially cytologic, are needed, as well as fieldwork, in order to understand these relationships and the variability in S. rupestris. Among the species in the flora, S. rupestris seems to be most closely related to S. sibirica (see discussion) and may also be allied to the S. arenicola complex (see discussion).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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