Mosses and liverworts, simple plants?
| by Jan Parmentier
with photographs by the author
Mosses (Bryophyta) are quite interesting, simple green land plants with leaves and a stem and always without roots. In many mosses, the leaves are only one cell thick, except for the midribs, which are sometimes present. So the leaves are easy objects for the microscope. The plant is normally attached to the ground by delicate, colourless or brown threads, the rhizoids.
There are two major groups in the Bryophyta: Mosses (Musci) and Liverworts (Hepaticae). See Footnote.
Most mosses are found in areas with a humid and a cold to moderate warm climate. In the tropics, mosses are found especially in the mountains. In Europe, the south western part of Ireland is a paradise for mosses.
Mosses can reproduce asexually, by means of small clusters of cells or plates of tissue which break away and germinate to become new plants. Especially liverworts do this.
|The normal, sexual method of reproduction
however, involves special organs, the antheridia and the
archegonia. These organs are the interesting parts for
the microscopist who is interested in the biology of
mosses. In the Musci the antheridium is the male organ, a
delicate sac in which the male gametes are formed. It has
a greyish or brown colour and an ovoid or globose form.
It is a spectacular sight to see the male gametes, with
two flagella, escape under the microscope from the
antheridium. These antheridia are normally accompanied by
numerous short filaments of cells, the paraphyses (see
The archegonium is easy to recognize, with a shape like a little bottle or flask. So look carefully with a hand lens among wet patches of mosses, archegonia and antheridia are often found in special cups of leaves.
paraphysis with archegonium
|I always try to study first some of the
common microscopical objects in detail, especially their
biology and then try to determine the names of the
species that are more difficult to find. So I studied
very common mosses to see some details of their
The male gametes, escaping from the antheridia, need water to reach the egg in the archegonium. After fertilization, the egg develops in most cases into a spore-containing capsule on a stalk called a seta. Capsule and seta together form the so called sporophyte. At maturity, the capsule sheds the spores as a fine dust. The spores can be held back in wet weather by a mechanism whereby the teeth of the capsule close it.
Mosses can have one or two rows of teeth, (images left and below), an important aspect for the determination.
|In most species the capsule (sporangium) peels open
in four sections (image above), exposing the spores and
the elaters, cells which have helically arranged moisture
absorbing wall thickenings. (Image below).
|These cells are sensitive to slight changes in
humidity, causing a twisting action that aids in
dispersing the spores. The elaters are initially attached
at both ends to the sporangium. Upon drying, one end of
each elater snaps loose from the center of the
sporangium, spreading the spores.
Marchantia polymorpha, a more complicated liverwort, is common in flowerpots in green houses, on moist bricks in gardens and on badly drained soils. On its leaves we can see small cups, (gemma cups) with small oval pieces of tissue, which can be spread by rain drops and become new plants
|This dioecious liverwort is
known immediately by the male and female
These umbrellas carry the male and female receptacles. The numerous sporogonia develop on the underside of the umbrellas; each capsule contains spores and elaters.
the male umbrella
the female umbrellas
You may call mosses simple plants, but important biological processes are easily studied by looking carefully at these sometimes fascinating plants.
Footnote: This is the classification adopted until recently and found in many books available on mosses and liverworts. The Phylum Bryophyta (mosses, liverworts and hornworts) has recently been split by taxonomists into three separate phyla: Bryophyta (mosses), Hepatophyta (liverworts) and Anthocerophyta (hornworts) e.g. see 'Margulis and Schwartz' in 'Further Reading' below. Return to article.
E.V.Watson, British Mosses and Liverworts. 2nd ed. Cambridge UP 1978.
A.J.E.Smith, The Moss Flora of Britain and Ireland, Cambridge UP, 1978.
H.N.Dixon, The Students Handbook of British Mosses, 3rd ed. Reprint Wheldon and Wesley 1970.
S.M.MacVicar, The Students Handbook of British Hepatics, 2nd ed. Reprint Wheldon and
D. Aichele, H.-W. Schwegler , Unsere Moos- und Farnpflanzen, Kosmos, Stuttgart 1984
W.D. Margadant, H.During, Beknopte flora van de Nederlandse Blad- en Levermossen,
KNNV 1982, Thieme, Zutphen.
P.H.Raven, R.F.Evert, S.E.Eichhorn, Biology of Plants, 5th ed., Worth Publishers, New York 1992.
L. Margulis, K.V. Schwartz, Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth, 3rd ed., W. H. Freeman, 1998. See Micscape Review.
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First published in July 1998 Micscape Magazine.
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