STARK, LLOYD R.* and CLAUDIO DELGADILLO M. Department of Biological Sciences, University of Nevada, Las Vegas, NV 89154-4004, USA; Instituto de Biologia, UNAM, Apartado Postal 70-233, Delagacion Coyoacan, 04510 Mexico, D.F. - Is Crossidium really an annual? Initial observations from the Mojave Desert.
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