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(Last modified: 29 Sep 1997)
Mosses and their allies are small green plants that are simlutaneously
overlooked and deeply appreciated by the typical nature lover. On the
one hand, very few people pay attention to individual moss plants
and species. On the other hand, it is the mosses that imbues our
forests with that wonderful lush "Rainforest" quality which soothes
the soul and softens the contours of the earth.
These wonderfully soft carpets of green are, in fact, Nature's second
line of attack in its war against rocks. After lichens have created a
foothold in rocks the mosses move in, ultimately becoming a layer of
topsoil for higher plants to take root. The mosses also hold loose
dirt in place, thus preventing landslides.
Ecologically and structurally, mosses are closer to lichens than they are to other
members of the plant kingdom. Both mosses and lichens depend upon
external moisture to transport nutrients. Because of this they
prefer damp places and have evolved special methods of dealing with
long dry periods. Higher plants, on the other hand, have specialized
organs for transporting fluid, allowing them to adapt to a wider
variety of habitats.
Bryophytes used to be classified as three classes of a single phylum,
Bryophyta. Modern texts, however, now assign each class to its
own phylum: Mosses (Bryophyta), Liverworts
(Hepatophyta), and Hornworts (Anthoceraphyta).
This reflects the current taxonomic wisdom that the Liverworts and
Hornworts are more primitive and only distantly related to Mosses and
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Mosses (Phylum: Bryophyta)
All plants reproduce through alternating generations. Nowhere is this
more apparent than in the mosses. The first generation, the
gametophyte, forms the green leafy structure we ordinarily
associate with moss. It produces a sperm and an egg (the gametes) which
unite, when conditions are right, to grow into the next generation:
the sporophyte or spore-bearing structure.
The moss sporophyte is typically a capsule growing on the end of a
stalk called the seta. The sporophyte contains no clorophyl of
its own: it grows parasitically on its gametophyte mother. As the
sporophyte dries out, the capsule release spores which will grow into a new
generation of gametophytes, if they germinate.
Mosses, the most common, diverse and advanced brypophytes, are
categorized into three classes: Peat Mosses
(Sphagnopsida), Granite Mosses (Andreaopsida),
and "True" Mosses (Bryopsida or
Shown: Class: Bryopsida; Order: Hypnales; Family: Brachythecia; Homolathecium nutalli (probably)
Leafy Liverworts (Phylum: Hepatophyta, Class: Jungermanniidae)
While people typically know what a moss is, few have even heard of
liverworts and hornworts.
These primitive plants function much like mosses and grow in the same
places, often intertwined with each other. The liverworts take on one
of two general forms, comprising the two classes of liverworts:
Jungermanniidea are leafy, like moss; Marchantiopsida
are leaf-like (thalloid) similar to foliose lichens.
The leafy liverworts look very much like mosses and, in fact, are
difficult to tell apart when only gametophytes are present. The
"leaves," however, are simpler than moss and dont have a midrib
(costa). The stalk of the sporophyte is translucent to white;
its capsule is typically black and egg-shaped. When it matures, the
capsule splits open into four equal quarters, releasing the spores to
The liverwort sporophyte shrivels up and disappears shortly after
releasing its spores. Because of this one hardly ever sees liverwort
sporophytes out of season. Moss sporophtyes, on the other hand, may
persist much longer.
Shown: Class: Jungermanniidea; Order: Jungermanniales; Family: Scapaniaceae; Scapania spp. (probably)
Leaf-like Liverworts (Phylum: Hepatophyta; Class: Marchantiopsida)
The leaf-like (thalloid) liverworts are, on the whole, more
substantial and easier to find than their leafy counterparts. The
gametophyte is flat, green and more-or-less strap-shaped. The body
may, however, branch out several times to round out the form.
When the gametophyte has become fertilized and is ready to produce its
sporophyte generation it may grow a tall green umbrella-shaped structure
called the carpocephalum. The sporophyte grows on the
underside of this structure, often completely hidden from view.
During the dry season, leaf-like liverworts may shrivel up and
completely disappear from view until the rains arrive again.
Thalloid liverworts are much easier to identify than their leafy
counterparts due to the wider variety of gametophyte shapes.
Shown: Class: Marchnatiopsida; Order: Marchantiales;
Family: Aytoniaceae; Asterella californica
Hornworts (Phylum: Anthoceraphyta)
Hornworts are very similar to liverworts but differ in the shape of
the sporophyte generation. Instead of generating spores in a capsule
atop a stalk, the hornwort generates spores inside a green horn-like stalk. When the spores mature the stalk splits, releasing the spores.
Under the microscope, hornwort cells look quite distinct as well: they
have a single, large chloroplast in each cell. Other plants typically
have many small chloroplasts per cell. This structure imparts a
particular quality of color and translucency to the body (thallus)
of the plant.
Hornworts are all grouped into a single class, Anthocerotae, containing a single order, Anthocerotales.
Shown: Class: Anthocerotae; Order: Anthocerotales;
Family: Anthocertaceae; Phaeoceros spp.
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