Sunday, February 19, 2017

Mosses of Central Florida 19. Rosulabryum capillare and R. pseudocapillare

Although the leafy shoots are buried within a
different moss, the presence of this Rosulabryum
is evident by the abundant and very large sporangia,
or capsules.
[For other mosses in this series, see the Table of Contents]

Like many other groups of mosses, those in the family Bryaceae are difficult to identify.  The available keys are highly technical and difficult to for non-specialists to follow.  The two species of Rosulabryum are presented together here because of those difficulties. R. capillare (Hedwig) J. R. Spence (Bryaceae) is common throughout North America, including Canada and our western states.  According to Flora North America, it is not found in Florida, but the related species R. pseudocapillare (Besch.) Ochyra takes its place.  However, numerous collections made in Florida have been identified by experts as R. capillare, along with many labeled as R. pseudocapillare.

Here, some leafy shoots have been isolated.
They are upright and radially symmetrical,
and the stalks of the sporangia arise from
the bases of the shoots. Sporangia are
symmetrical, cylindric and nodding.
Rosulabryum pseudocapillare typically has numerous thread-like reproductive structures (filiform gemmae) in the upper leaf axils, at least when not producing sporangia, while those of R. capillare do not.

Rosulabryum is common in Central Florida  and produces abundant nodding, nearly cylindrical sporangia (capsules) in the springtime.  It can be found most readily in wet soil at the margins of receding ponds, forming mounds of upright stems. It might almost be considered weedy, as it also pops up readily in pots containing wet, organic soil, and in wet soil along sidewalks.

Rosulabryum was formerly included in the genus Bryum, having been segregated out on details that are hard to follow in the formal keys.  In Florida, only Bryum argenteum remains in the original genus, which incidentally gives its name to the entire clade of non-vascular plants we call Bryophytes.  B. argenteum differs from Rosulabryum in its more compact growth form, its grayish coloration, and leaves that press flat against the stem when dry.  The dried leaves of Rosulabryum twist around the stem.

Nearly ripe sporangia of Rosulabryum
are cylindrical and bright green.
The leaves of Rosulabryum become twisted when dry.
The other segregate from Bryum found in Florida is Gemmabryum, but it apparently forms sporangia less often than Rosulabryum, relying more on asexual bulbils and gemmae for reproduction.  When sporangia do appear, they are more egg- or pear-shaped.  The leaves in Gemmabryum are also said to be pressed flat against the stem when dry, as in Bryum argenteum, rather than being twisted like in Rosulabryum.

Leaves of Rosulabryum, like other members
of the famly, have a strong midrib (or costa).
Leaves in the Bryaceae have a strong midrib, and the leaf cells are mostly large, more-or-less rectangular or rhomboidal in shape, thin-walled, and with numerous distinct chloroplasts.  This, along with the upright, mound-forming stems and the nodding sporangia, makes members of the family fairly easy to recognize, though the genera and species are more difficult to distinguish.

Leaf cells of Rosulabryum, are thin-willed,
revealing many distinct chloroplasts within.

The leafy shoots of Rosulabryum peudocapillare produce
many thread like reproductive structures called filiform gemmae,
while those of R. capillare rarely do.