Wednesday, June 22, 2016

Mosses of Central Florida 17. Sphagnum strictum

Sphagnum strictum occurs in dry woodlands, and forms whitish branch heads
that are more compact than those of S. palustre.
Sphagnum strictum Sull. (Sphagnaceae) occurs throughout northern Florida, as far south as
Collier County.  It is distinctive within the local species for its dry habitat preference and tolerance of desiccation. It occurs in oak hammocks and other dry woodlands, on dry, sandy soil.  It most often has a very whitish color, as its leaves consist of large water storage cells within which the photosynthetic cells are confined to very narrow strands. 

When dry, the branch heads become more feathery.  Photo by Alan Franck.
(from Franck 3787 (USF)
Sphagnum strictum produces sporangia in the spring, while S. palustre produces them in the Fall. 
The reddish sporangia of Sphagnum strictum appear
in the spring.

The leaf of Sphagnum strictum is composed mostly of large water-storage
cells, which appear as empty.  The cells are reinforced by fibrils wrapped
around each cell.  What appear to be thick cell walls are actually the very
narrow photosynthetic cells.

Mosses of Central Florida 16. Sphagnum palustre

The leafy shoots of  Sphagnum palustre consist of
a compact head of short shoots, with a ring of
longer shoots hanging below.  Each shoot in this
complex consists of a series of closely spaced
ovate leaves.
Sphagnum palustre L (Sphagnaceae) is one of the most common, and most abundant sphagnum mosses in central and northern Florida.  Outside of the state, it extends into to the boreal zone of Canada, and contributes to the massive sphagnum bogs found there.

 Sphagnum species are notoriously difficult to identify, however, and it is probably safe to say that only Sphagnum specialists can use the technical keys to identify a specimen, and even then there is uncertainty and disagreement.  The characters that distinguish particular species, and even whole groups of species, are anatomical in nature, requiring specialized skills to view and interpret.

On a local level, however, particularly in Florida, there are typically only a few species in an area, occupying slightly different habitats, and differing in the size, shape, and coloration of the leafy shoots.  25 species are presently known to occur in Florida, 18 of which extend into central Florida.  Few extend much further south than Hillsborough and Polk Counties, but P. palustre  reaches its southern limit in Highlands County. These numbers and distributions are only approximate, as the herbarium records involved have not all been verified by specialists.  Additional collecting will also add to our knowledge of the distributions of species. 

An extensive colony of Sphagnum palustre near the Hillsborough River, occurring in a flat
seepage zone.
Sphagnum palustre is distinguished from other species in Hillsborough County by its larger shoot size, and the distinctive shape of its terminal cluster of branches. It also occurs, in our area, in a unique habitat zone: in relatively flat, continuously wet zones, such as a seepage area, which is neither often flooded nor completely desiccated.  S. palustre produces sporangia in the Fall. 

Another common species found nearby, S. strictum occurs in drier habitats and has smaller, distinctly whitish clusters of shoots (profile of this species to follow immediately after this).  A third species, yet to be identified, occurs in intermediate habitats.

Although the species are difficult to identify, the genus is unmistakable, particularly with a quick look at a leaf under a microscope.  The leaves are just one cell thick, but differentiated into two kinds of cells.  The green, photosynthetic cells are long and narrow, and form an interconnected network between much larger water-storage cells.

Special note: the mosses have now been added to the Atlas of Florida Plants, where you can see the county by county distributions of each species.  We are also slowly adding photographs to the database.