I.
Introduction
This section
was designed to give interested folks answers to common questions
about mosses as well as clarify what a moss is and what it is
not. For instance, one could read about "Spanish moss"
growing profusely over vegetation in Florida
and the eventual death it brings its plant victims, consequently
developing a negative opinion about moss in general. People
and moss have been engaging in this struggle for years and the
mosses deserve to have their story told. Let's see if you
change your mind as we more fully explore what a moss truly is.
By the way, "Spanish moss" is a flowering plant related
to pineapple which produces small flowers, not a moss at all
II.
What are Mosses?
When asked
to visualize what a plant is, many of us picture a herbaceous
plant such as a sunflower, or a woody plant such as a maple tree.
We think of "plants" as possessing roots, a stem (or
trunk), flowers, fruit, and seeds. Most of us do not automatically
think of the plants that grow on rocks, rooftops, concrete, and
any other moisture-laden area; however, this opportunistic bunch,
choosing many eclectic substrates, exists. Their leaves
are mostly one cell thick, they have no true roots, stems, flowers,
or fruit, and instead of seeds they have spores. "They"
are the mosses; the plants we see forming "green carpets"
with thin wiry upright stems supporting a brown capsule that appears
to be wearing a hat. For more information,
read on, and consult Richardson
(1981) Schofield
(1992), Shaw and Goffinet
(2000), and
Sterling
(1955). For
in-depth information on the ecology of mosses, see Janice Glime's
online book, Bryophyte
Ecology.
III. How do mosses
reproduce and spread?
Mosses spread in multiple ways, but unlike flowering plants, they
depend on moisture to sexually reproduce. Mosses reproduce
by spores, which are analogous to the flowering plant's seed;
however, moss spores are single celled and more primitive than
the seed. Spores are housed in the brown capsule that sits
on the seta. As the spores ripen they are dispersed from
the capsule, and some land in areas where there is enough moisture
for them to grow. The young moss looks like a very thin
tangled mass of branching green
hairs. Buds will appear next on the green hairs, from which
tiny stalks and slim leaves will grow. Some mosses have
cups on their tops that produce sperm, these are male plants.
The female counterpart has eggs between her overlapping leaves.
Water is a necessity for fertilization; as the sperm become mature
they have to swim to the eggs to fertilize them. The
fertilized egg then produces the stalked brown capsule.
Mosses also spread asexually by sending out new shoots in the
spring from last years plants as well as fragmentation.
Pieces of the moss body can break off, move by wind or water,
and start a new plant if moisture permits.
V. How do Mosses Acquire
Nutrients?
Mosses also
have different mechanisms they use for acquiring nutrients.
Some mosses are able to take up nutrients from water flowing over
them, thus they have very effective absorptive surfaces.
Other mosses, such as Polytrichum, sequester nutrients
directly from the soil or substrate on which they are growing
and transfer the nutrients to their growing tips. With this
in mind we can see that the physical and chemical nature of the
substrate as well as its water holding capacity are extremely
important in establishment of mosses.
V.
Where do mosses live?
Now that
we have seen the resilience mosses possess via their multiple
modes of reproduction, it is easier to fathom that mosses can
live anywhere from the Arctic Circle to the tropical forests at
the equator. Mosses can be found around hot springs, at
the bottom of lakes, on rocks, sand dunes, trees and, even in
a few cases, sea water. And of course those of us who live
in the Pacific Northwest know that mosses thrive in moist temperate
forests.
An opportunist, mosses grow on our trees, sidewalks, garden, rooftops,
and everywhere in between. The two main requirements of
a moss are sufficient moisture and accessible nutrients.
For example, the moist environment of a rooftop shaded by trees
seems just fine for mosses. Not only does the rooftop stay
perpetually moist, but nutrients are also supplemented from the
ash that fireplace chimneys produce (Schofield, 1973). See section regarding
Mosses
on Rooftops. Shingles composed of wood,
asbestos, and conglomerate composition all make suitable homes
for moss; however, metallic roofs or those with an abundance of
tar will discourage moss growth. But the tarred roof must
be smooth to assure that mosses will not colonize in the cracks
and crevices. Mosses prefer to colonize shingles above the eaves,
on detritus that builds up in the eaves' troughs or other depressions.
Mosses will be at their best in the winter when there is plenty
of water, little light, and low temperatures. In summer
mosses dry out and become dormant.
VI. What
are mosses good for?
Unknown to most of us, mosses actually have many uses, from ecological
to medical with a suite of common household uses in between.
One of the better known ecological uses of moss is as bioindicators
of air pollution, such as those caused by factory emissions. They
are very good indicators of acid rain damage to an ecosystem as
well. Mosses are also used as erosion control agents as
they aid in moisture control and stabilization of soil that would
either be wind blown or washed away by water. Mosses occupy
an important ecological niche in arctic and subarctic ecosystems
where moss symbionts provide most nitrogen fixation in these ecosystems,
as compared to the leguminous associations that are responsible
for this job in temperate regions. Mosses can also be used
as bioindicators of water pollution and treatment of wastewater.
Throughout history mosses have been used in horticulture because
they are beneficial to the soil. Mosses increase the amount
of water soil can store and improve soil's nutrient holding capacity.
In the United States mosses are not highly acclaimed for their use in gardening. But ornamental and garden uses of mosses are becoming more common. See the book Moss Gardening by George Schenk.
Mosses are aesthetically beautiful and provide an attractive covering over soil and concrete surfaces that would otherwise be bare. We should feel lucky here in the Pacific Northwest that this unique and ornate organism grows easily and can provide much diversity among our gardens, rooftops, and sidewalks. See section on Encouraging Mosses.
Like mosses, liverworts are bryophytes. So they are closely related, but differ in some important aspects of form and reproduction. Leafy liverworts look like mosses to the untrained eye, but thalloid liverworts are green ribbon-like, branched plants, usually growing along the ground. Marchantia and Conocephalum are two of the most conspicuous thalloid liverworts. Conocephalum is illustrated at right, while photos of Marchantia are in the section of this website on liverworts in greenhouses.
Although lichens often grow with mosses, and people commonly confuse them, they are quite different. Lichens are a mutualistic association between a fungus and an alga or cyanobacteria. This site contains a few references to lichens, but we recommend that you visit LichenLand to learn more about them. See our examples of living with lichens.