This Bryophyte field trip was led by James Shevock, a Botanist who is presently focused on Bryology, and has an association with the California Academy of Sciences.

Leaving the parking lot, our group crossed Bon Tempe Dam, taking the fire road leading to the beginning of the Kent Trail. Soon we joined the Rocky Ridge trail, going about one mile uphill along it. Jim identified many species of bryophytes, educating us about moss ecology and the plants’ natural history.

Bryophytes do not have seeds or flowers; they reproduce by spores. Most are inconspicuous, non-vascular plants that have existed on Earth for millions of years. Understanding of bryophyte life cycles, evolution, dispersal, and diversity is increasing now that experts are using various new genetic research methods. There are about 25,000 species of bryophytes worldwide, with about 200 species known in Marin. Some Marin mosses survive from an era before the advent of our Mediterranean climate. Such species are rare here, found in microhabitats, but are often widespread elsewhere, such as Mexico or even the Mediterranean area. Mosses growing on rocks capture dust and moisture, resulting in soil development. The oldest moss parts are found at the bottom of any perennial thick, cushiony colonies. They can contain antifreeze-like compounds that allow survival from desiccation, then facilitate rehydration. These compounds are not palatable, so very few animals eat mosses and liverworts, but many invertebrates do live among them; some aquatic species even shelter fish at Lake Tahoe.

The macroscopic moss, liverwort, and hornwort plants that we see are haploid (containing a single set of unpaired chromosomes) and are called the gametophyte generation. They have male and female reproductive organs called antheridia and archegonia, which produce eggs and sperm, respectively. All bryophytes depend on water for sexual reproduction. The motile male gametes are released into the local environment and must successfully navigate from the male to the female sex organs. Fertilization results in a diploid stage called the sporophyte, each one of which sprouts from a single fertilized egg. The sporophyte eventually produces spores that grow into a new generation of gametophytes. In contrast, the ferns, gymnosperms, and flowering plants that we see are all the sporophyte generation. Their gametophyte stages are minute.

Moss sporophytes have a more complex structure, and may even have water-conducting cells. Some sporophytes have a slender stipe and a capsule head attached to a maternal gametophyte. Sporophytes can last up to a year, annd are dependent on the gametophyte for protection and nutrition. Capsules typically contain 30 to 50,000 spores, although a few species have up to 250,000 spores per capsule. These tiny moss spores can withstand desiccation.

Mosses stay in equilibrium with their environment, soaking up water quickly and drying out quickly. Hyaline “leaf” tips are adaptations for acquiring water after desiccation. Mosses look very different when wet and dry, and are not dead when dry. When dry, some mosses resemble mousetails (Isothecium spp., Claopodium whippleanum); some look like dried violins, with curled stems and leaves (Dendroalsia abientina); and some resemble a shag carpet, the leaves open and twisted (Homalothecium spp.) Moss “leaf” shapes are specific to each family and are spirally arranged around the “stem.” Generally, moss leaves are only one cell thick. Seasonally submerged species (rheophytes) occur in which the leaf margin and rib may be thickened to 4-6 cells for protection (Scleropodium obtusifolium).

Thalloid liverworts, such as Asterella spp., are of multicellular thickness from top to bottom.

Leafy liverworts have “leaves” in a flat plane along the “stem,” sometimes with a second or third row of leaves underneath the top ones. The “leaf” tips may be bifurcate or lobed (Porella navicularis). Cells may contain oil bodies.

Hornworts do not have leaves or midribs, and their sporophytes are pointed linear structures. The one we saw, a Phaeoceros sp., has a blue green algal symbiont in the fleshy thalli.


The largest Bryophyte herbarium in the world is in Helsinki! Let’s go!

More information can be found in  “Special Issue: Bryophytes”, Fremontia 31(3), July 2003″.

Check out the CNPS Bryophyte Chapter.

Report prepared by Susan Schlosser.

Photos by Margo Bors  except where noted.

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Field Trip Species List


Alsia californica

Antitrichia californica

Atrichum selwynii

Claopodium whippleanum

Dendroalsia abietina

Dicranoweisia cirrata

Didymodon vinealis

Fissidens crispus

Homalothecium pinnatifidum

Homalothecium nuttallii

Grimmia trichophylla

Isothecium cristatum

Isothecium stoloniferum

Kindbergia oregana

Kindbergia praelonga

Nogopterum gracile

Orthotrichum lyellii

Pohlia wahlenbergii

Polytrichum juniperinum

Rosulabryum sp.

Scleropodium obtusifolium


Species mentioned but not seen:

Bryolawtonia vancouveriensis (on base of very large Umbellularia californica burls)

Pseudoleskeella serpentinensis (on large serpentine boulders)



Phaeoceros sp.



Asterella californica

Fossombronia sp.

Porella navicularis