What are bryophytes?
Bryophytes include mosses, liverworts, and hornworts. Researchers of the tree of life debate whether these three groups are a whole and complete branch of the tree of life. A fourth group, the vascular plants, might arise from within the ‘bryophytes’. Bryophytes are the land plants that are not vascular plants.
Parts of a moss
The gametophyte is the leafy part of a moss that does most of the photosynthesizing and that occupies space. It makes eggs and/or sperm, called gametes. It has a stem or stems, and is anchored to the ground by rhizoids, which are not roots since they do not have vascular tissue. The calyptra is also gametophytic. Gametophytic tissue has one set of chromosomes (N). Sporophytic tissue has two sets of chromsomes (2N). In mosses, the sporophyte consists of a long sturdy seta with a capsule on top. The capsule opens by the shedding of its operculum, revealing a peristome that liberates the spores.
Moss life cycle
Mosses and other bryophytes have life cycles that are dominated by the gametophyte phase. The green leafy part of a moss is the gametophyte, the plant that makes gametes (eggs and/or sperm). The phase that makes spores, the sporophyte, lives out its entire life attached to and dependent on its mother gametophyte. The sporophytes in mosses consist of a capsule usually on a long wiry stalk, called a seta. However, in the Marchantia shown below, the seta never expands, and the capsules are nearly buried in the gametophytic structure that holds them aloft.
Parts of a liverwort
Liverworts come in several types. Here is diagrammed a leafy liverwort. Leafy liverworts may have leaves in two ranks or in three ranks. If the latter, the underleaves may be smaller or otherwise differentiated. The way in which the leaves overlap varies among taxa. In some the leading edge is on top and the arrangement is said to be incubus; in others the leading edge is under the leaf that is in front of it when seen from above and is said to be succubus; still other leafy liverworts have transversely inserted leaves. Leaves in many groups are lobed, and in a few the lobing is very deep, making the whole shoot appear cloaked in narrow lobing. Bilobed leaves may be folded making the leaves complicate-bilobed.
Liverwort life cycle
Liverworts, like mosses, have a life cycle dominated by the gametophyte, the gamete-producing phase. The sporophytes are attached to the gametophytes. They consist of a capsule, sometimes on a stalk that resembles a glass noodle.
Lichens, Selaginella, and other non-bryophytes
Lichens and mosses tend to have similar ecologies, living on surfaces that dry out. They are not, however, close relatives. Lichens are a symbiosis between a fungus and an alga. Selgainella is sometimes called a ‘spike-moss’, but it is not a moss. It is a vascular plant, and the leafy part you see is a sporophyte. Like lichens and mosses, many Selaginella are desiccation tolerant. A number of other organisms that are not bryophytes are also sometimes referred to as as though they were mosses, including some algae of ponds and streams.
Most bryophytes are more or less able to be thoroughly dried out and then come back to life. The plants are desiccation tolerant, and they more or less follow the hydration of their environment, i.e., they are poikilohydric. In contrast, most vascular plants are homeohydric. Even a cactus has cells inside that are kept moist all the time. Cacti are desiccation resistant, by having a very thick waxy cuticle.
How to section a leaf
- Moisten your specimen
- Pluck off some leaves
- Move an individual moistened leaf to a dry place on your slide
- Place the pin so that only the distal quarter of the leaf is peaking out
- Chop down with the razor held parallel to the pin
- Roll the tiniest amount; chop; repeat
Readings for beginners
• A basic introduction to bryophytes in California was presented in Fremontia 31(3).
• For a textbook, Vanderpoorten A & Goffinet B. 2009. Introduction to Bryophytes. Cambridge University Press.
• Schofield WB. 2002. Field Guide to Liverwort Genera of Pacific North America. University of Washington Press.
• A photo guide that works pretty well in California’s redwood forest as well as in its intended range: McCune B & Hutten M. 2018. Common mosses of Western Oregon and Washington. Wild Blueberry Media.
Unfortunately, there is not yet any introductory field guide to mosses in California.
Trail Guides, etc.
• Redwood Park, East Bay