The first significant rains of the season will draw the mushrooms up and will revive our shriveled lichens and bryophytes.
Mosses, liverworts, and hornworts are grouped together as bryophytes (“BRY-o-fights”).
Bryophytes need places that are wet at least part of the year -- which includes a lot of territory in the damp areas of the Pacific Northwest. However, they don’t need much more, making them good pioneering plants that build soil and offer habitat in otherwise bare surfaces.
Small and non-woody, bryophytes don’t have a well-developed vascular system, the tubes that allow fluids to move from one part of a plant to another.
More interestingly, the whole issue of sexual reproduction is different for bryophytes than for most familiar plants.
First, a thumbnail sketch of basic sex on a cellular level. You might think that all plant and animal cells have two sets of DNA, two sets of chromosomes. But that’s not the whole story.
Just like in us, in most plants the vast majority of the cells do have a double set of chromosomes. Cells with a double set of chromosomes are described as “diploid” (based on the Greek word, “diplous,” for “double”). The flowering parts of diploid plants make special cells with only one set of chromosomes—the seeds and pollen.
Cells with a only one set of chromosomes are described as “haploid” (based on the Greek word, “haploos,” for “single”). (In humans and other animals, eggs and sperm are haploid cells.) Whether plant or animal, the haploid cells get together to make a new individual diploid organism.
The flowering plants and ferns that we take note of are diploid: they have two sets of chromosomes in most cells. (A column for another time, the life cycle of ferns and their allies is quite different from the flowering plants.)
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Bryophytes are unusual in that the conspicuous, leafy plants are haploid: the larger, permanent parts of mosses and their relatives have only one set of chromosomes. In bryophytes, only small, temporary structures are diploid.
Have you ever noticed the wiry stalks sticking out of the moss, each wire topped with a tiny, cylindrical capsule? The stalks and capsules are the only diploid part of moss; most of the moss is haploid. Liverworts, too, are mostly haploid, with only very small parts that are diploid. In that way, bryophytes use a life-cycle system that’s opposite of ours.
While the diploid part -- the fruiting bodies -- of mosses are capsules on stalks, the diploid part of many liverworts are shaped like cups or like tiny umbrellas or golf tees, and the diploid part of hornworts are shaped like long horns.
While mosses are quite familiar to most people, liverworts and hornworts are rather less familiar. Further, the “leafy” liverworts look very much like moss and can be difficult to identify unless they’re fruiting.
Besides the shapes of their fruiting bodies, leafy liverworts and mosses also differ in how the leaves are arranged: Leafy liverworts have their leaves in two flat rows (sometimes there’s a third row tucked beneath them, on the underside); moss leaves are generally arranged in spirals around the “stem” (though the spirals are sometimes squashed). Leafy liverwort leaves do not have a midrib and most moss leaves do.
“Scaly” liverworts look a bit like miniscule bits of green snakeskin, and hornworts look like scaly liverworts with horns.
And, yes, some species of bryophytes can be identified only by using a microscope to pick out tiny distinguishing features.
The most familiar bryophyte group, the mosses, come in a huge variety: The northwestern region of North America is home to about 900 species of moss. And most are quite beautiful -- beautiful enough to star in terrariums and other indoor and outdoor gardens.
While they certainly appear similar to casual observation, recent DNA evidence indicates mosses, liverworts, and hornworts are not very closely related. Bryophytes do share a need for damp, however, and they’ll all welcome the start of the wet season.