Mosses do not have roots and, in their absence, the plants anchor to a surface with rhyzoids attached to a substrate. Consequently,mosses can thrive on surfaces as dissimilar as rocks, concrete walks, and masonry walls. Mosses survive long periods of drought, dehydrate, and sustain prolonged dormancy, to then resume photosynthesis upon re-hydration. Moss infestations prevail as sponge-like bio-masses which, when microscopically viewed in cross-section, provide a densely packed labyrinth of minuscule voids and interstices. Given that the surface-to-volume ratios of voids vary inversely with size and shape, moss infestations comparatively interface to their ambient environment with an extraordinarily high biomass surface relative to volume. This key attribute, in the absence of root hairs to absorb water and leaf stomata to respire carbon dioxide and oxygen, serves to sustain photosynthesis by extended surface adsorption.
When moss first colonizes an area it produces a black, slimy mat across the area before the green vegetative structures form. The green structures grow into branch-like filaments called protonema. These are the threadlike structures that bud out and develop into the gametophyte. The protonema of mosses are extensive, resembling green algae, and may persist for months. Mosses can take many shapes and forms. Stems and leaves of moss are complex, most having conducting strands, midribs, and a great diversity of cell form. Shoots develop from tetrahedral cells, and this results in three leaf arrangements. Leaves may be grouped in pairs, threes, and even sets of five. In the majority of mosses, leaves are not arranged in regular rows. Except for the midribs, leaves are one cell thick, with most or all of the cells containing chloroplasts. There are essentially two growth forms for moss plants. In one the stems are basically erect, with just one upright stem per plant or with the initial erect stem producing some branches, depending on
the species, giving the individual plant a tufty or shrubby appearance. In the other growth form the moss will have mostly trailing stems. If the stems cling to the substrate the overall appearance, to the naked eye, will be of a creeping plant but in some species they hang, almost curtain-like, from branches .
Another common moss strategy for structural support is to grow very densely. So, like academic communities, they grow progressively larger and denser, maintaining their continued existence by sheer bulk without having any real roots in the environment which supports them.
They have also developed elaborate designs for clinging to each other, so that the entire mass behaves like a foam rubber pillow – conforming to the slightest pressure, but springing back to business as usual when the pressure is removed.
