Species of Crossidium have long been considered plants of annual habit. This attribute probably derives from their short stature and frequent sexual reproduction. Populations of Crossidium crassinerve represent the dominant species of bryophyte in some of the hottest and driest regions known from the North American continent: along the north-facing slopes of low elevation washes in the Mojave Desert. Annual precipitation, all rain, averages approximately 100 mm/year in these areas, with growth and reproduction in the mosses restricted to the cooler, wetter months of winter and early spring. The annual nature predicts that such populations should appear in early winter and senesce by spring or summer. Cores of populations were removed, placed in 20 mL scintillation vials, and vigorously shaken in water for several minutes to remove soil particles while not severing organic connections of individuals. The upper few mm of stem was dissected to reveal innate growth interval distinctions based upon color changes of leaves and stems. Allocation was assessed to stems and leaves based on number, length, and dry biomass. Yearly growth intervals were approximately 0.10 - 0.20 mm long, with yearly leaf allocation consisting of about 12 leaves. Laminal filaments tended to remain chlorophyllose longer than the blade. Individual ramets routinely extended 10 mm below the substrate surface. Conservative calculations indicate that many ramets in a well established population are on the order of 50 years old. Longer term experiments are underway in which (i) individual ramets are marked and periodically photographed in retractable population cores; and (ii) the surface of the population is cleared of ramets and regrowth monitored.

Key words: allocation, annual, Crossidium crassinerve, desert, longevity, perennial