More Mosses: Division Bryophyta.
All moss gametophytes have two distinct phases as the protonema
(see moss life cycle picture in previous post) and the leafy gametophyte
. In true mosses, the protonema cells are in a single layer, and the branching resembles filamentous green algae. Leafy gametophytes develop from bud like structures on the protonema. In some mosses the protonemata (plural) persist and assume the major photosynthetic role, and the gametophytes are minute. Protonemata are characteristic of all mosses, some liverworts, but not hornworts.
The True Mosses: Class Bryidae.
The true moss gametophyte is leafy and typically upright rather than flattened as in the leafy liverworts. Three initial ranks of leaves after axial twisting resemble a spiral arrangement - like phyllotaxy, but instead the stem twists. Not so apparent in some aquatic mosses. In many species the stems of gametophytes and sporophytes have a strand of water conducting hydroid cells (dead when mature, become empty and thus useful as a pipe). In some genera, leptoids – living food conducting cells, surround the hydroids.
Cushiony mosses (below and above). Gametophytes are erect and little branching, usually bearing terminal sporophytes.
Feathery Mosses. (below) Plants are creeping, leaves typically branched often superficially resembling ferns, often hanging as epiphytes from trees.
The Granite Mosses: Class Andreaeidae.
Occurring in mountainous or arctic regions, often on granite rocks, the genus Andreaea consist of only about 100 species. The gametophytes closely resemble true mosses but the sporophyte lacks a true seta (stem) and is raised instead on a stalk of gametophyte tissue, the pseudopodium. The spore release mechanism also differs from other mosses with 4 ‘slits’ (vertical lines of weaker cells among stronger cells) that open widely when the capsule is dry, releasing windborne spores, and closing when it is moist. A second genus found in Alaska, Andreaobryum, has one (discovered) species. It has a sporophyte with a true seta, and its capsule splits to the apex.
The Peat Mosses: Class Sphagnidae.
Diverging from the main line of moss evolution very early, the genus Sphagnum holds approximately 350 species of mosses. The gametophyte stems bear clusters of branches, often five per node, resembling a ‘mop like’ head. The plants form bright green or reddish clumps in boggy ground. The leaves lack midribs and consist of large dead cells surrounded by a narrow band of green, or red, living cells. The dead cells are what gives sphagnum it’s water holding capacity (20 times the dried weight), the pores and thickenings in these readily fill with water. In living plants the dead cells keep them turgid.
Sphagnum sporophytes are also distinctive with spherical red to blackish brown capsules raised on a pseudopodium which is part of the gametophyte as with the granite mosses.
An estimate of 1% of the worlds soil (1/2 the land mass of the United States) is peat bog. Peat bog can have a pH as low as 4 due to sphagnum releasing H+ ions and altering their environment. Peat is the accumulation of sphagnum, as well as sedges, grasses, reeds and other plants that grow with sphagnum. Recent experimentation and microscopy by IC Mag member Microbeman shows peat is also loaded with microbial life.