Bryophytes (Mosses, Liverworts and Hornworts)
In Colorado, there are three types of bryophytes, mosses, liverworts and hornworts. There are about 14,000 species of mosses in the world and about 400 have been documented in Colorado. There are about 7,000 species of liverworts world-wide and about 104 species have been found here. And only 2 hornwort species have been documented in Colorado from the 104 species found in the rest of the world. It is important to note that there are, and have been, very few bryologists in Colorado, so the species that live in the state are not well documented. New state records of new species are found every year.
Mosses look superficially like small flowering plants with roots called rhyzoids (rhyzoids’ only function is to attach the plant to the substrate) stems and leaves. The rhyzoids are branched and usually are colored reddish brown to dark brown. The leaves can be arranged in two to four rows along the stem, but more often are spirally arranged around the stem. Their leaves are simple, never lobed and often have a midvein called a costa. The costa can be single, double, or absent and extends from just above the base, to the tip, or beyond the tip ending as a hair-point. When you see a moss in this form, you are looking at the gametophyte generation which has one set of chromosomes (see reproduction below).
In the process of reproduction, the moss grows a sporophyte generation at the tip of gametophyte the plant or in the axils of the branches. The sporophyte consists of the foot, which attaches to the, a stalk, called a seta, and a capsule. The seta is often brown, reddish or reddish purple. The capsule varies in shape from tubular to ovoid and can stand erect, horizontal or pendant at the top of the seta.
Liverworts can have a leafy form with leaves and stems like mosses, or can be thallose, in which case they form a strap, ribbon or kidney shape that lies flat on the ground. The leafy liverworts’ leaves are arranged in two or three rows, are often lobed, and do not have a costa. Their rhyzoids are unbranched and are usually colorless. The sporophyte generation also consists of a seta and capsule, but the seta is fragile and collapses when the spores are released.
Hornworts are always thallose, and the male and female parts develop internally. The sporophyte is unlike the sporophytes of mosses and lichens, developing into long tubes that extend above the plant and look superficially like grass.
Characteristics of Mosses
One of the most important characteristics of mosses is that they are non-vascular plants. Unlike our Colorado flowering plants, ferns and conifers, which have a well-developed internal vascular system to transport water and mineral from the roots, photosynthesized sugars from the leaves, and to provide structural support, mosses do not have a vascular system. They are small, sometimes as small as one to two milometers tall, but in Colorado, usually 1 to 8 centimeters tall. Because they are so small and usually only a few cells thick, water can be conducted to the plant by capillary action rather than using a vascular system.
Vascular and non-vascular plants have two different strategies for dealing with the variation of the availability of water on land. Vascular plants control the amount of water in their cells by conducting water from their roots in the soil to their leaves. This strategy works well as long as the soil is hydrated, but can desiccate and kill the plant when the soil is too dry.
Bryophytes, on the other hand do nothing to control the amount of water in their cells, but have the ability to shut down their metabolism when water is not available. They are either fully turgid or desiccated. Like lichens, they can shut down their metabolism for years, instantly starting photosynthesis when water becomes available again. Many species can go from complete dessication to fully turgid and photosynthesizing in just a few seconds when water is added.
The second most important characteristic of mosses (as well as liverworts and hornworts) is that their reproductive cycle is an alternation of gametophyte and sporophyte generations, with the dominance of the gametophyte generation (discussed in the next section). Flowering plants and conifers’ life cycle is dominated by a life form with two chromosomes whereas bryophytes dominant life form has a single chromosome.
Angiosperms and conifers reproductive processes occur featuring a variety of techniques involving wind, water and various insects and animals to transfer pollen from one plant to another to foster cross pollination. The result is a high level of genetic variability in the population making the plants adaptable to changes in the environment.
Bryophytes, on the other hand, require free water for the sperm to swim to the ovary. One would think that this is not as an effective reproductive strategy, until one considers that the mosses and bryophytes have been around for 340 million years, whereas the angiosperms have only been around for 150 years. They compensate for this limitation by having extensive phenotypic variability, that is, plants with the same genes can display a large variation in their characteristics to adapt to their environment.
In addition, mosses rely much more on asexual reproduction that do angiosperms. In fact, new moss plants can grow from almost any part of the moss leaves or stems, and also reproduce from all sorts of special organs including gemmae, bulbils, specialized branchlets and tubers attached to the leaves, stems or underground rhyzoids. Reliance on asexual reproduction results in relatively slow rates of evolution in morphology. The fossil record of mosses indicate that their ancient forms are very similiar to present-day mosses.
Because they are small in size, have no extensive root systems, and have the ability to immediately respond to the presence or absence of water, mosses have an extremely close relationship with their environment and are adept at living in specific micro-habitats. For the same reason, though, they are not adept at spreading and often do not fill their local habitat.
Mosses are also very social organisms. This is partly due to the fact that with the use of so much asexual reproduction a clump of mosses will have the same genetic variability, and the survival of the individual is closely related to the survival of the group. There are strong indications that moss plants communicate by using chemicals called pheremones. In addition to that, however, there are indications that the presence of other nearby bryophytes nearby are beneficial. When trying to identify moss species, it is important to make sure that the clump of mosses you are looking at aren’t multiple species.
New Research: Mosses Use Pollinators!
Recent research has found that mosses use pheremones to attract microscopic insect-like creatures called springtails to help with fertilization. The springtail is attracted to the male part of the plant using using a pheremone perfume The moss sperm attaches to the springtail’s legs. And then, the springail is then attracted to the female part of the plant using a different pheremone, delivering the sperm to the ovary. This may have been a precursor to the angiosperms use of bees and other insects to deliver the sperm to the ovary in flowering plants. In angiosperms we know that the flower exudes nectar to attract insects, but we do not know yet if the mosses use a similar substance to attract springtails.
Some Moss Species Identifiable by Eye
Photos are in alphabetical order by scientific name
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Silvery Bryum Moss (Bryum argenteum)
Silvery Bryum Moss (Bryum argenteum), Bryaceae Family. Grows from plains to alpine on the eastern and western slopes. This is a common species found in cracks in sidewalks but also sometimes found in cliff crevices and other dry, exposed, sandy or gravelly places. It is easily identified as the leaves are white rather than green and all of the stems stand straight up and are packed tightly together. It is the same whether wet (on the right) or dry (on the left). Photo by Mo Ewing.
Some Liverwort Species
Marsupella sphacelata is a liverwort in the Jungermanniaceae Family is an uncommon liverwort with the common name in Great Britain of Speckled Rustwort, probably because its color which is greenish-brown to rust brown. It is usually prostrate growing in mats. In Colorado it has been found only in the alpine along a lake and in spruce-fir forests. This moss is not listed by the Colorado Natural Heritage Program as rare, but it has been collected only twice in Colorado, which would give it an S1 rank. Photo by Mo Ewing at 12,040' on North Mountain, Greenhorn Wilderness.
Plagiobryoides renauldii, an acrocarpous moss not previously known from Colorado, was found at Unaweep Seep State Natural Area in Mesa County by a group of bryologists, including myself, Paula Lehr, and Ron Wittmann from Colorado, along with Karen Blisard and Russ Kleinman from New Mexico.
From Aquilegia Volume 45 No 3, Summer 2021
The primary difference between angiosperms and bryophytes are in their reproductive cycle. In flowering plants the life cycle is dominated by the sporophyte generation, which has two sets of chromosomes (called diploid). When the plant produces a flower, the chromosomes are split into male and female parts in a process called meiosis, each with one set of chromosomes, the male part, called the stamen, produce pollen, and the female part, called the pistil, produce the ovary. This is the angiosperm’s gametophyte generation (haploid), when the male and female parts have only one set of chromosomes and live totally within the structure of the diploid flower.
In the next step the ovary is fertilized by the sperm by pollination. Some angiosperms can self-pollinate, but others require wind, rain, insects, birds, and other natural processes to transport the pollen from the stamens to the ovaries. Once the sperm has fertilized the ovary, the seed that is produced has two sets of chromosomes in a process called mitosis and the next sporophyte generation is created.
Unlike the angiosperms, bryophytes alternate between the sporophyte and gametophyte generations, each of which has its own physical structure. Bryophytes are also dominated by the gametophyte generation which has one set of chromosomes (haploid) and is what you see as the small green moss, liverwort or hornwort plant in the field. This gametophyte grows two reproductive structures, the antheridia which is the male organ, and the archegonia which is the female organ. Sometimes these structures grow on the same plant, sometimes on separate plants. The antheridia produces sperm, which is released and swims in a thin film of water to the archegonia. The archegonia releases chemicals to attract the sperm. Unlike angiosperms, bryophytes require free water outside of the plant for fertilization.
After the mature egg cell is fertilized by the sperm, a sporophyte develops that looks quite different from the gametophyte. In mosses, the sporophyte consists of a foot (which attaches to the gametophyte), a seta (stalk) and a capsule in which the spores develop. It has two sets of chromosomes and is diploid. The sporophyte plant never detaches from its gametophyte parent. Meiosis takes place within the sporophyte capsule, cutting the chromosomes in half and creating a spore which is haploid. The spores are released into the air or in water (one method, using “splash cups” see Polytrichum commune) landing nearby and growing a new gametophyte plant.
Because of their small size, their phenotypic plasticity, and their relative simplicity, mosses can be a challenge to identify. When we are out in the field identifying angiosperms (flowering plants), most of the time we have the flower, fruit and vegitative parts to aid in identification. The color, number and shape of the petals, number shape and arrangement of the sepals, the pistils and stamens, or we have the fruit and its shape, size, and type, and we almost always have stems and leaves with their shapes, both simple and compound, different edges, and their arrangement on the stem. Most of the time all of these parts are nice and big, and can all be seen with the naked eye, or with a 20x hand lens.
Mosses, however, are often only in a vegetative state, and do not have have and “flowering” parts to help with identification. That leaves only the rhyzoids, stems and leaves. In fact, a good bryologist, can identify most mosses from their vegetative sate only, but some species require both the gametophyte and sporophyte for positive identification. In addition to that, mosses are often really small so you can’t see much of anything at all, even with a hand lens. The unfortunated reality is that if you want to identify many moss species, you will need to use a disecting and compound microscopes to look at leaf cells and other tiny moss parts.
On the other hand, identifying mosses, like identifying challenging angiosperms (grasses, sedges and all those damn yellow asters) is challenging and fun and can be done by the amateur in small bites. There are many genera of mosses, and even some species, that can be identified because they have unique characteristics which can be identified with the naked eye or using a hand lens. Identifying a moss genus is a great accomplishment in itself, so you can start there. Don’t bother with tiny mosses, go into our local forests and look at big ones. And finally, find a mentor to help you identify mosses. There is one group in Colorado that has recently formed called the Rocky Mountain Mossers some of whom are members of CoNPS and meet on-line and go out on field trips to identify and collect mosses. If you are interested in learning some mosses, contact Mo Ewing (firstname.lastname@example.org).
To get started, peruse our Moss Species photos on this page. We are adding some common species that have characteristics that are easy to identify.
Where They Grow
Because mosses require free water around the plant to reproduce, you would think that they only occur in places with a lot of water. However, they are found in micro-habitats just about everywhere in Colorado because of their ability to shut down their metabolism and wait for water to come. Because mosses do not compete well with other large plants, you will not find many on the eastern plains, thickly vegetated mountain meadows, or exposed south-facing slopes of the foothills. Even in wet areas where there is a lot of competition from sedges for instance, you won’t find a lot of mosses in the thick sedges, but you will find them in small shady micro-habitats, or the edges of small rocky rivulets, or on the sides or tops of hummocks, where the sedges do not grow.
Mosses do grow on a wide variety of substrates. If you live in a city or town, the first moss you might find is Bryum argenteum, which grows in cracks in the sidewalk. You will find Grimmia species like Grimmia montana on rocks in full sun. Dicranum tauricum is a very small species which grows on decaying wood and often has leaves with broken off tips. Splachnum sphaericum is a rare moss in Colorado which likes to grow on moose dung. Many species live on soil, humus or litter as you would expect, but some prefer in living on bark, mostly near the bases of trees like Pylaisiella polyantha. Sphagnum and Meesia species prefer the peat in fens and other mosses such as Fontinalis and Warnstorfia are totally aquatic living in slow- and fast-moving streams.
Mosses find micro-habitats in dozens of places. As you would expect, you will find them in lots of wet places such as, fens, peatlands, wet meadows and willow carrs. under water in ponds, pools and lakes, and along the sides (in the splash zone) of streamsides, streambeds, river banks and in the spray of waterfalls. Canyons and ravines are good places to look because of shade they produce, especially on north-facing walls, and forests are full of mosses for the same reason. Many species of mosses love cliffs and crevices, rock outcrops, ledges and boulders (Hedwigia ciliata).
As you might not expect, many species thrive in exposed, sunny sites, plains, grasslands and pastures (Ceratodon purpureus). But the exposed areas that mosses like the best are in tundra, snow-melt areas, where it is cooler and where there is more moisture (Rhytidium rugosum). Another unexpected place to find mosses is in desert regions of the western slope. Syntrichia caninervis grows under sagebrush in desert areas where the snow collects in the winter. It forms part of the cryogenic soil crusts that are so important in holding bare soil in place.
And finally, some mosses that have weird tastes. Funaria hygrometrica loves recently burned areas, and Syntrichia caninervis lives in the desert in western Colorado under sagebrush where a bit of snow has collected in the winter. Most of the time it is totally dessicated and is a major component of cryptobiotic soil.