Genus GrimmiaGenus GRIMMIA, Ehrh.
The species of the Genus Grimmia sometimes form conspicuous gray tufts, often hoary from the white hair-points which terminate the leaves; sometimes they form soft fragile patches on exposed rocks of higher mountain regions. The tufts vary in size from little dense cushions one-third of an inch high, to the mats of Gr. hypnoides, whose stems attain a length of eight inches.
The dingy colour of their leaves, tipped with long or short white hairs is their most striking character. The chlorophyll is not only absent from the hair-point but often from the apex of the leaf-blade as well, thus adding to the grayish-white appearance of the tufts. The plants are usually short, with forked stems, crowded with lance-shaped leaves, frequently thickened along the margin, which is mostly entire; the vein is percurrent or extends into the transparent hair; the cells of the lower part are rectangular, of the upper part small, often obscure.
The generic name was given in honour of J. F. C. Grimm, a German botanist, who was a physician of Gotha.
The spore-cases are oval and smooth, borne on arched or straight pedicels. The peristome consists of sixteen red, lanceshaped teeth, entire or cleft at the apex and often perforated below.
There are about two hundred and forty species known at present, fifteen of them in North America.
Grimmia Apocarpa Moss