Monographs Details: Sphagnum L.
Authority: Sharp, Aaron J., et al. 1994. The Moss Flora of Mexico. Part One: Sphagnales to Bryales. Mem. New York Bot. Gard. 69 (1)
Family:Sphagnaceae
Scientific Name:Sphagnum L.
Description:Genus Description - Moderately robust plants of wet habitats, usually in carpets, cushions, or hummocks, rarely submerged or floating. Stems erect (or in aquatic species weak and spreading), forked and fasciculately branched, consisting of an inner hyaline parenchyma enveloped by a wood cylinder of thick-walled prosenchyma and a cortex of 1 or more layers of large, empty, quadrate to short-rectangular, thin-walled cells that may be spirally fibrillose and porose or efibrillose and, most often, without pores, the cortical cells rarely poorly differentiated, elongate-rectangular and firm-walled. Branches in fascicles spirally arranged around the stem and crowded in a headlike tuft at the stem tip, some branches spreading, others (of more slender construction) ± pendent. Branch cortex usually in 1 layer, consisting of large, empty, thin-walled hyaline cells that may be spirally fibrillose and generally porose or efibrillose with some cells retortlike, that is, larger and apically porose at the end of a protruding neck, rarely all cells apically porose but not retortlike. Branch leaves crowded, spirally inserted in a 2/5 phyllotaxy, concave, oblong-lanceolate to rounded-elliptic, consisting of linear green cells arranged in a network enclosing large, empty, rhomboid hyaline cells that are reinforced within by annular fibrils and perforated on 1 or both surfaces by round to elliptic pores (or very rarely without fibrils and/or pores), bordered by about 2-3 rows of linear cells or sometimes by a single row of elongate cells apparently digested away at their outer margins (forming a resorption furrow). Stem leaves less crowded, usually considerably differentiated from branch leaves in size, shape, and structure, the hyaline cells sometimes subdivided, generally with a lesser development of pores and fibrils, often extensively resorbed on 1 or both surfaces, resulting in wrinkling (as membrane pleats), thin-spots, irregular membrane gaps, or (rarely) round to elliptic pores. Dioicous or monoicous. Paraphyses none. Antheridial branches densely foliate and often catkinlike, the leaves not much differentiated but often highly colored, single or in fascicles of 2-3, the antheridia globose, long-stalked, borne singly at the side of each leaf of the catkin. Perichaetial branches very short, 1-2 or more per fascicle, bearing at the apex 1-5 narrow, flask-shaped archegonia; perichaetial leaves large and sheathing, broadly Ungulate, with hyaline cells generally poorly differentiated from the green cells and usually lacking fibrils or pores. Sporophyte consisting of a sessile capsule and a massive foot embedded in the tip of the perichaetial branch, which elongates to elevate the mature capsule beyond the perichaetium; capsules globose, becoming cylindric to urceolate when dry and empty, reddish, dark-brown, or black, without annulus or peristome; operculum nearly flat; wall of several layers of cells, without intercellular spaces, usually with a large number of somewhat sunken pseudostomata (in the lower half or nearly throughout). Spores about 18-12 µm, tetrahedral, nearly smooth to finely papillose-roughened, explosively discharged as the capsule shrinks on drying. Calyptra a delicate, hyaline membrane closely investing the capsule and irregularly rupturing at its maturity.

Discussion:

The genus Sphagnum, consisting of about 200 species, is well represented in the north, especially in glaciated regions of impeded drainage. Many species of broad, northern distribution range disjunctively southward into the tropical highlands, but a good number are completely tropical in distribution. Most of the Sphagna of Mexico are disjuncts from the north. Only 12 species have been found thus far in Mexico, but phytogeographic probabilities are such that at least half a dozen others of broad distribution and nearby occurrence can be expected there. It is reasonable to expect some additional species to show up as disjuncts from the Coastal Plain of the American Southeast, possibly also from the Southern Appalachian Mountains, and a few others from the Antillean and Andean floras. Species of Mexico, as well as those most likely to occur in Mexico but not yet found there, are given notice in recent papers by Crum (1978,1980a, 1980b).

Sphagnum has a reputation for taxonomic difficulty, yet with basic understanding of structures and some experience, one can name the species with ease. (See Crum, 1988, A Focus on Peatlands and Peat Mosses, for an explanation of structures useful in the taxonomy of the genus.) Most of them can be recognized at sight, owing to rather obvious differences in size, color, form, and habitat preference. The microscopic characters useful in taxonomy are best observed on staining. A saturated water solution of Crystal Violet gives a good contrast.