Mosses

Mosses are small, non-vascular land plants in division Bryophyta. They are widespread in moist, shaded environments and often form green carpets on soil, rocks, and decaying wood. The moss body, or thallus, is typically a leafy, low-growing gametophyte composed of simple stems with whorled or spiral leaves that are usually one cell thick. They lack true xylem and phloem and rely on diffusion to move water and nutrients. Rhizoids anchor the plant and aid in water absorption.

Life cycle: Mosses reproduce by alternation of generations. The dominant stage is the haploid gametophyte, producing male antheridia and female archegonia. Water is required for fertilization, as sperm swim briefly to archegonia. The fertilized egg develops into a diploid sporophyte, which grows as a stalk (seta) bearing a capsule (sporangium) on the gametophyte. In many species, the capsule is capped by an operculum and releases spores through a ring of peristome teeth that respond to humidity. Spores give rise to new gametophyte plants. In some species, they also reproduce asexually by fragmentation or by gemmae, small propagules produced in cups on the plant surface.

Ecology and significance: Mosses occupy a key role in many ecosystems. They help retain moisture, contribute to soil formation, and in peatlands, species such as Sphagnum contribute to long-term carbon storage. They provide microhabitats for invertebrates and microorganisms and can act as pioneer species on damp rocks and bare soil. They are used horticulturally and decoratively, and some species have traditional or cultural uses. Many moss species are sensitive to pollution and habitat disturbance and are monitored as indicators of environmental health.