The growth and survival of four populations of the summer annual spikeweed, Centromadia fitchii was studied in Butte (Oroville Airport and Table Mountain sites) and Tehama counties (New Vina and Barn Pasture sites) in the Northern Sacramento Valley of California during 2000 and 2001. In both years, survival and morphological features of 50 plants at four sites were measured biweekly, and soil samples and climatological data from the sites were compared to these measurements. Most plants studied were long-lived and successfully reproduced in 2000, but all plants died before flowering in May 2001. Life tables and survivorship curves were created for the four sites in 2000 and 2001. Based on Log Rank test results, plant survival was significantly higher (p < .05) at all sites in 2000 than in 2001. During both years, Oroville Airport had significantly higher survival (p < .05) than Barn Pasture and New Vina, but was not different from Table Mountain. Table Mountain survival in 2001 was significantly higher (p < .05) than at both Barn Pasture and New Vina, and Barn Pasture survival was significantly higher (p < .05) than that of New Vina. Summer needle-like leaves and glandular trichomes, both morphological adaptations to drought, formed in April, 2000, but a full month later in May, 2001. No major differences occurred between sites or years in total monthly precipitation or mean monthly temperature, but temperatures over 32 C were less frequent in May 2000 than in May 2001. Soils at Butte County sites were characterized as sandy loam, and those at Tehama County sites were loam. Soil differences between sites may help explain survival patterns observed within years. Variation in climate, and gland and needle-like leaf formation between years is most likely responsible for the low survival observed at all sites in 2001.

Key words: Centromadia fitchii, environmental factors, spikeweed, summer annual, survival