Tuesday, July 5, 2016

Mosses of Central Florida 18. Bryum argenteum

The fine, compact cushions of Bryum argenteum are a distinctive
grayish-green.  This specimen was collected in gravel at the base
of a palm tree along a walkway above a saltwater channel in
Tampa (Essig 20160503-1 (USF).
Bryum argenteum Hedw. (Bryaceae) forms compact, fine-textured cushions in exposed areas of poor soil, gravel, or even concrete. It is easily recognized by it's grayish green color, in contrast to the bright green of most other members of the family in our area.  It is the only member of Bryum in Florida.  Other species formerly included in the genus have been segregated out into other genera, including Gemmabryum and Rosulabryum.  It is distinguished from these latter genera by its smaller, more compact dimensions, and the leaves that are more-or-less pressed to the stem, like the scale leaves of a juniper.
The leaf cells of Bryum argenteum, are large, thin-walled,
and filled with chloroplasts. 
Like other members of the family the cells of the leaf are large, and thin-walled, and there is a prominent midrib.  Also very distinctive in this family are the nodding capsules.  This species does not produce capsules very often.  The accompanying picture of capsules is from a specimen collected in Bronx, NY.
The capsules of Bryum argenteum, like
most members of the family Bryaceae,
are symmetrical but nodding by a bend in
the uppar stalk.  From Ahles s.n.,
Bronx, NY 1949 (USF)