STARK, LLOYD R. Department of Biological Sciences, University of Nevada, Las Vegas, NV 89154-4004. - Widespread sporophyte abortion following summer rains in Mojave Desert populations of Grimmia orbicularis.
The normal phenological sequence in Grimmia orbicularis
restricts sporophyte elongation in Mojave Desert populations to the
winter months, when low temperatures and sufficient rainfall occur.
During 1997, however, heavy rainfall was restricted to the summer
months. Coincident with these summer rains, over 50% of the cohort
sporophytes aborted, with the time of abortion traceable to the period
that followed the summer rains. Abortive sporophytes were arrested at
or near the end of the embryonic phase, just prior to seta elongation.
It is postulated that the unusually high frequency of abortive
sporophytes was caused by the absence of winter rains in conjunction
with torrential summer rains. The accelerated hydration/rehydration
cycles that occur during summer rains allow insufficient time for
desiccation recovery processes critical for sporophyte survival.
Key words: Grimmia orbicularis, Mojave Desert, monoecy, phenology, sporophyte abortion