BSC 314 Lecture Notes - Lecture 53: Capillary Action, Jungermanniales, The Leaves
27 Jun 2018
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Phylogeny of Bryophytes
With a sketchy fossil record, bryophyte phylogeny is based primarily on molecular
sequencing of rRNA and morphology of extant species—with hypotheses changing as
new data accumulate. Researchers generally believe that the charophyte coleochaete ‐
group of the green algae gave rise to the plants and that the bryophytes diverged from
the common ancestor to vascular plants sometime during the Silurian, over 430 million
years ago. Opinions differ concerning phylogenies within the bryophyte group, however.
One view believes the three bryophyte groups had separate evolutionary origins and
that only the mosses are more closely related to the plants. The bryophytes seem to
have evolved during a time in which gametophyte characteristics were important for
plant survival, whereas the vascular plants evolved when conditions favored the
sporophyte portion of the life cycle.
Ecology of Bryophytes
As descendants of the early land plants, bryophytes have retained the ability to adapt to
a variety of habitats and environments. They live as understory components on the
ground or as epiphytes in forests worldwide, but flourish most luxuriantly in moist warm‐
temperate and tropical habitats. Many of the liverworts and some species of moss are
pioneers on newly burned ground while still other mosses colonize bare rock surfaces
where their presence accelerates the erosion of rock to soil. The few desert dwellers
rely on the condensation of dew on their surfaces to supply their metabolic water needs.
In these sites, production of sporophytes is rare and the species spread primarily by
vegetative means.
Mosses and liverworts are prominent in the arctic tundra on bare, dry surfaces while
farther south in the circumpolar boreal conifer forest (taiga) and its southern extensions,
the northern conifer forests, mosses constitute most of the biomass of the bogs and wet
understory of the trees.
Land Plants Without Vascular Tissues
Bryophytes are small, low growing plants of mostly moist environments in the temperate‐
and tropical zones where they grow on the ground and as epiphytes on the trees and
undergrowth. In the alpine and boreal zones, bryophytes often are the dominant life
form. Some bryophytes are desert dwellers, and a few are aquatic; none are marine.
The bryophytes are of botanical interest because their ancestors apparently were
among the first land plants. The existing species today have some green algal features
and some vascular plant attributes making them intermediates—more complex than
green algae, but not quite vascular plants. Once thought to be monophyletic, the
bryophytes are now recognized as having three independent lineages.
Characteristics
Bryophytes are plants because they are photosynthetic with chlorophylls a and b, store
starch, are multicellular, develop from embryos, have sporic meiosis—an alternation of
generations—and cellulose cell walls. Some mosses have simple water and food
conduction type cells (but these are not the same as the xylem and phloem tissues of ‐
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Document Summary
With a sketchy fossil record, bryophyte phylogeny is based primarily on molecular sequencing of rrna and morphology of extant species with hypotheses changing as new data accumulate. Researchers generally believe that the charophyte coleochaete group of the green algae gave rise to the plants and that the bryophytes diverged from the common ancestor to vascular plants sometime during the silurian, over 430 million years ago. Opinions differ concerning phylogenies within the bryophyte group, however. One view believes the three bryophyte groups had separate evolutionary origins and that only the mosses are more closely related to the plants. The bryophytes seem to have evolved during a time in which gametophyte characteristics were important for plant survival, whereas the vascular plants evolved when conditions favored the sporophyte portion of the life cycle. As descendants of the early land plants, bryophytes have retained the ability to adapt to a variety of habitats and environments.
