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To fully hydrate patches of Crossidium crassinerve in the Mojave Desert, a rain event of at least 2.0 mm was required. When patches were hydrated for at least 3 days, mean daily ambient maximum/minimum temperatures were only 15.6/7.5 degrees C. During the summer, patch temperatures exceeded ambient temperatures, whereas during the cooler months patch temperatures were lower than ambient temperatures, with degree of patch hydration not a factor in patch temperature. During patch hydration, mean surface patch temperature ranged from -3 to 14 degrees C. With few exceptions, patch hydroperiod (duration of patch hydration) was restricted to the cooler months spanning October to April, with the mean patch hydroperiod (among five patches) ranging from 3.7 to 4.9 days. While the most commonly recorded dry period was <25 days, Crossidium patches experienced longer periods of desiccation on nine occasions, with the longest period being 191 days. During a late winter rain event, patches dried slowly over a period of several days, whereas during a summer rain event, patches dried in as few as 3 h. Over the 4-year period, 248 sporophytes were initiated, with all but four of these from two patches. Only nine of these initiated sporophytes survived to disperse spores, with mortality attributed to embryonic abortion (69%) and capsule herbivory (30%).