3. Selaginella rupestris (L.) Spring (rock spikemoss) Pl.
19c,d; Map 67
Leaves spirally alternate along the stems, all similar in shape and size,
3.0–4.5 mm long, linear-lanceolate to subulate, appressed, the margins minutely
ciliate, the tip with a thin white bristle, the midvein extending to the tip.
Strobili square in cross-section, the leaves 4-ranked, the megasporangia
usually occurring in the rank on the underside of the strobilus. Megaspores
orangish yellow, with a dense network of ridges on the surface. Microspores
Scattered throughout the Ozark and Ozark Border Divisions (eastern and northern
U.S. and Canada west to Wyoming). Dry, exposed sandstone, igneous,
and chert glades, rocky ledges, and rock outcrops in prairies.
populations of this species either do not produce microsporangia or produce
them very rarely, and the number of megaspores is usually 2 per sporangium,
rather than 4. Tryon (1955) speculated that these plants may reproduce
apomictically. In the Appalachian Mountains,
where plants regularly produce microsporangia, they tend to be found toward the
tips of the strobili.
A single collection by G. C. Broadhead labeled as having been collected in Adair County
(in the Missouri Botanical Garden Herbarium) is not included for distributional
purposes. Although Broadhead collected in Missouri
during the mid-1800s, this specimen also contains plants of S. underwoodii,
a species endemic to the southwestern U.S.
and adjacent Mexico.
The locality listed on the label, “shaded damp hillsides,” is not typical for S.
rupestris. The specimen is thought to contain the two different species
from two different states and a label with a mixture of data from both of these