Acaulon muticum (Hedwig) Muller Hal. var. rufescens (A. Jaeger) H.A. Crum

Acaulon muticum is a minute, budlike, ephemeral moss, which grows on disturbed soil along paths and on bare patches amongst grasses. The leaves are deeply concave and tightly overlap one another, completely surrounding the small spherical sporophyte capsule on its short seta. Plants may be scattered or in tight clusters, and are green when young and when shaded, reddish when mature and in full sun.

Scroll down for more photos (click to enlarge) and descriptions of habitat, plants, leaves, sporophytes, distribution map, name origin, and similar species.

Habitat:  Acaulon muticum is found on soil in disturbed habitats, such as along trails or surrounding ground squirrel burrow entrances, in partial shade or full sun.

Habit:  Acaulon muticum may grow as scattered individual plants or in tight clusters forming a virtual carpet. Early in the season and when growing in the shade, plants are a bright yellow green. Later in the season, particularly when growing in full sun, plants become reddish brown.

Plants:  Acaulon muticum plants are minute (to 2 mm tall) and budlike, with the leaves tightly overlapping one another and completely enveloping the tiny sporophyte within. Early in the season and when growing in the shade, plants are a bright yellow green. Later in the season, particularly when growing in full sun, plants become reddish brown, leaves eventually degrading, thus revealing the sporophytes.

Leaves:  The inner, larger leaves of Acaulon muticum are deeply concave, often slightly toothed and recurved near the tips, ending in a short, stout point called an apiculus. In cross section the cell walls facing away from the stem (abaxial) are significantly thicker than those facing the stem.

Sporophytes:  Acaulon muticum sporophytes are short, simple and completely enveloped within the plant until the end of the season, when the leaves begin to decay. The capsule is spherical and chestnut brown, atop a very short seta, and degrades at maturity, releasing the spores.

Distribution:  Acaulon muticum is found throughout California and the west coast, as well as in North America and Europe, however Acaulon muticum var. rufescens is restricted to N. America.

Name: The genus name Acaulon is derived from the Greek a for without and kaulos for stem, referring to the lack of stems on the plants. The species epithet muticum comes from the Latin word muticus for blunt, presumably referring to the relatively blunt leaf tips, without long awns.

Similar Species in Santa Barbara County

Tortula acaulon, another ephemeral moss growing in similar habitat, is slightly larger, and less budlike, with longer, flatter leaves with longer hyaline awns, giving it a furrier look from a distance.

Stegonia hyalinotricha, another ephemeral moss growing in similar habitat, is similarly budlike, but the leaves have very long hyaline awns

References and Further Reading

Acaulon muticum var. rufescens, Richard Zander, Flora of North America Vol. 27, www.efloras.org, also available on the new Flora of North America site here.

California Mosses, Bill and Nancy Malcolm, Jim Shevock and Dan Norris. Available for purchase from the California Native Plant Society here.

Contributions toward a Bryoflora of California II. A Key to the Mosses, Daniel H. Norris and James R. Shevock, Madrono 51(2): 133-269. 2004. Available for purchase  here.