BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

IX. LOWER SPORE PLANTS

Subclass True Mosses, or Bryid Mosses (Bryidae)

The gametophytes of true mosses are represented by leafy shoots ranging in length from a few millimeters to half a meter. Uniseriate multicellular, simple or branched rhizoids grow from the stem either in its lower part or along its entire length.

The leaves are sessile, attached to the stem by their base, which may sometimes form a sheath, auricles, or wings. The leaf blade of most true mosses features a costa (midrib), and a border runs along the margin. The leaf blade (except for the midrib and border) is always unistratose (single-layered). The midrib consists of phloem, xylem, and mechanical Cells, over which green lamellar outgrowths, known as assimilators, are located.

In addition to leaves, the stems of certain bryid mosses bear green leaf-like or filamentous appendages called paraphyllia, which perform Photosynthesis and absorb Water.

The stems of many Bryidae have a complex Structure. For instance, the stem of Hair-cap moss is covered on the outside by an epidermis, beneath which lie the cortex and a vascular bundle. The outer Cells of the cortex have thickened walls and function as mechanical tissue. The outer part of the vascular bundle forms a ring of living thin-walled phloem cells lacking sieve plates, through which organic substances are transported. The phloem is followed by 1–2 layers of starch-sheath cells. The center contains the xylem, formed by elongated dead cells with strongly thickened lateral and thin transverse walls, which conduct water and mineral salts.

Antheridia and archegonia, along with paraphyses and surrounding leaves, are located at the apexes of the shoots under the protection of perichaetial leaves, forming reproductive buds. Biflagellate spermatozoa mature within the antheridia. Fertilization requires water. As a result, in most mosses, a single sporogonium develops from the zygote within the reproductive bud. It consists of a FOOT, a seta, and a capsule covered at the top by the calyptra, which is the remnant of the archegonial neck.

The capsule consists of a neck, an apophysis, a urn, and an operculum. The neck is the lower narrowed part of the capsule transitioning into the seta. The apophysis is the swollen lower part (base) of the capsule that separates the urn and the seta. The urn is the part of the capsule where spores develop as a result of Meiosis. A columella is located in the center of the urn. It arises from the apophysis, and in Polytrichaceae mosses, its upper part forms an epiphragma that covers the urn.

Upon spore maturation in most true mosses, the capsule opens by shedding the operculum. Cilia or Teeth are located along the margin of the urn, forming a toothed peristome. The teeth may be arranged in a single row (single peristome) or two rows (double peristome). The peristome teeth perform hygroscopic movements, which facilitate the shedding and dispersal of spores by wind, water, or insects.

Under favorable conditions, a spore germinates into a filamentous protonema. Leafy gametophyte shoots develop from buds formed on the protonema.

The subclass of true mosses comprises about 14,000 species, of which over 500 species are found in Ukraine. Among them, There are also aquatic mosses.