Plant of the Week
Mosses
When considering plants, mosses are
often overlooked and although many are quite
small, they play a vital role in most
ecosystems. We usually think of mosses as
conspicuous components of wet habitats,
rainforests, swamps, creek and river banks,
but when you know what to look for, and how
to look, you will find mosses in some pretty
harsh environments: in deserts; alpine, arctic
and subantarctic regions; even round volcanic
fumaroles. Don’t forget, they are plants and
they do carry out photosynthesis but they
produce spores rather than flowers and they
don’t have an internal conducting (vascular)
system.
Hypnodendron \vitiense subsp. australe
Bryophytes
are
probably
more
important than many other divisions of the
plant kingdom because of their interaction with water. Mosses are able to hold
amazing quantities of moisture between their minute, often finely sculptured,
overlapping leaves and fine, massed rhizoids (root like structures). In rainforests,
mosses reduce the velocity of water and minimize erosion processes; mosses and
liverworts in tree canopies can absorb moisture as if they were giant sponges,
humidifying the forest for long periods after rain. In deserts, where they are
Ptychomnion aciculare
Mosses from Werrikimbe
National Park in
northern NSW
Dawsonia superba
components of biological soil crusts (complex combinations of algae, fungi, lichens,
mosses and liverworts), mosses have the ability to rapidly absorb and store moisture
from dew or fog. They stabilize desert soils and protect dunes from erosion by wind
and flash flooding. They also contribute to the fertility of desert soils, and enhance
the survival of ephemeral, annual and perennial seedlings.
The ancestors of modern day mosses are believed to have moved from the sea
to the land in the late Ordovician ~ 450 million years before present, although the
Carboniferous is more usually accepted for origin and expansion of mosses.
Until recently, mosses were considered to be one class (Musci) of the division
Bryophyta of the Plant Kingdom. The other two classes were the liverworts
(Hepaticae) and the hornworts (Anthocerotae). Using modern molecular
techniques, botanists have now elevated each of these classes to divisions of the plant
kingdom, so now only mosses belong to the Division Bryophyta, liverworts are
placed in the Division Marchantiophyta and hornworts in the Division
Anthocerophyta.
All three divisions are now collectively referred to as
“Embryophytes”, that is, land plants that do not have a vascular system. Some
mosses do have elements of conducting systems, but as they lack lignin, they are not
considered to be true “vascular plants”.
There are currently a number of bryophyte studies being undertaken by
researchers in the Department of Biological Sciences at Macquarie University. These
include a study of bryophyte distribution in Nothofagus moorei forests of northern
NSW by Ross Peacock and Alison Downing; taxonomy of the Trematodon, Pohlia,
Mniaceae and Sematophyllaceae by Helen Ramsay; studies of bryophytes of
biological soil crusts of the Gurbantunggut Desert of north-western China by Alison
Downing working with Professor Zhang Yuan Ming and other researchers and
students of the Chinese Academy of Sciences; and bryophytes of sub-Antarctic
islands (Macquarie Island, Heard Island and Iles Kerguelen) by Patricia Selkirk.
Professor R. D. Seppelt
from
the
Australian
Antarctic Division in
Hobart, has very kindly
allowed us to display some
of
his
scientific
illustrations of Australian
mosses.
Nothofagus moorei (Antarctic Beech) forest in
Werrikimbe National Park in northern NSW. Mosses
are abundant on beech buttresses, fallen logs and rocks.
Alison & Kevin Downing,
Department of Biological
Sciences, 21.05.2012