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BRYOPHYTA is the collective name given to a group of closely related
cryptogamous plants we call mosses (MUSCI) and liverworts (HEPATICAE).
These bryophytes are believed to have evolved directly from the green
algae which is the simplest form of aquatic plant life.
Thus the mosses and liverworts are the first land-based forms
of plant life we know of. A few
species of mosses are still aquatic, but most mosses can survive long periods of
dry weather successfully because their structure is such that they absorb
moisture very quickly and soon "revive" again, even after long periods
of drought. All mosses, besides
requiring a continuing source of moisture for their survival, also need the
medium of water for sexual reproduction. The
sperm, in order to reach the nearest ovum, must swim through a film of moisture
(from rain or dew) over the surface of the plant (see the Life
Cycle page). It is obvious then, that mosses flourish most readily in moist and cool
habitats.
Another significant feature of
the bryophytes is that they do not take nourishment from the soil directly as
the fibro-vascular plants do by means of a central core and an elaborate root
system. The bryophytes have no
roots as such, nor a central core, but absorb all the nutrients they require
from the air and from the minerals washed by the rain from the foliage of trees
and other plant life overhead. Many
mosses also have their stems coated with a thick coat of very fine hairs called
tomentum which collects and stores moisture for the plant's nourishment.
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