Bryophytes (liverworts, mosses, and hornworts) are non-vascular
plants that appeared on earth over 450 million years ago.
LEARNING OBJECTIVE [ edit ]
Describe the characteristics of bryophytes
KEY POINTS [ edit ]
Bryophytes are the closest-living relative of early terrestrial plants; liverworts were the first
Bryophytes, probably appearing during the Ordovician period.
Bryophytes fossil formation is improbable since they do not possess lignin.
Bryophytes thrive in mostly-damp habitats; however, somespecies can live in deserts while others
can inhabit hostile environments such as the tundra.
Bryophytes are nonvascular because they do not have tracheids; instead, water
and nutrients circulate inside specialized conducting cells.
In a bryophyte, all the vegetative organs belong to thegametophyte, which is the dominant and
most familiar form; the sporophyte appears for only a short period.
The sporophyte is dependent on the gametophyte and remains permanently attached to it in
order to gain nutrition and protection.
TERMS [ edit ]
sporangium
a case, capsule, or container in which spores are produced by an organism
tracheid
elongated cells in the xylem of vascular plants that serve in the transport of water and mineral
salts
bryophyte
seedless, nonvascular plants that are the closest extant relative of early terrestrial plants
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Bryophytes
Bryophytes are the group of seedles plants
that are the closest-extant relative of early
terrestrial plants. The first bryophytes
(liverworts) probably appeared in the
Ordovician period, about 450 million
years ago. However, because they lack of
lignin and other resistant structures,
bryophyte fossil formation is improbable
and the fossil record is poor. Some spores
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protected by sporopollenin have survived and are attributed to early bryophytes. By the
Silurian period, however, vascular plants had spread through the continents. This compelling
fact is used as evidence that non-vascular plants must have preceded the Silurian period.
More than 25,000 species of bryophytes thrive in mostly-damp habitats, although some live
in deserts. They constitute the major flora of inhospitable environments like the tundra
where their small size and tolerance to desiccation offer distinct advantages. They generally
lack lignin and do not have actual tracheids (xylem cells specialized for water conduction).
Rather, water and nutrients circulate inside specialized conducting cells. Although the term
non-tracheophyte is more accurate, bryophytes are commonly called non-vascular plants.
In a bryophyte, all the conspicuous vegetative organs, including the photosynthetic leaf-like
structures, the thallus, stem, and the rhizoid that anchors the plant to its substrate, belong to
thehaploid organism, or gametophyte. The sporophyte is barely noticeable. Thus, the
gametophyte is the dominant and most familiar form; the sporophyte appears for only a short
period. The gametes formed by bryophytes swim with a flagellum. Thesporangium, the
multicellular sexual reproductive structure, is present in bryophytes and absent in the
majority of algae. The sporophyte embryo also remains attached to the parent plant, which
protects and nourishes it. This is a characteristic of land plants. The bryophytes are divided
into three phyla: the liverworts (Hepaticophyta), the hornworts (Anthocerotophyta), and the
mosses (true Bryophyta).
Moss
Mosses (true bryophyta) are one of the three kinds of bryophytes (along with liverworts and hornworts).
This image shows a moss growing on a dry stone wall.