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The similarities and differences in seed bank structure across four locations in the North American deserts (Curlew Valley, Utah in the Great Basin; Rock Valley, Nevada in the Mojave Desert; Silverbell, Arizona in the Sonoran Desert; and Jornada, New Mexico in the Chihuahuan Desert) were compared using published data. Species composition at Curlew Valley was most distinctive among the four study sites. In all four sites, average seed size decreased in this order: shrub, herbaceous perennial, and annual species. Mean seed sizes were similar across the Curlew Valley, Rock Valley and Silverbell sites but much smaller at the Jornada site. Most species have small seeds, but the number of seeds varied greatly among these small-seeded species; i.e. seeds of these species could be highly abundant or very rare in the seed banks. In contrast, very few species have large seeds and the seeds of these species were always rare. The possible roles of underlying soil and climatic factors in structuring desert seed bank structure are discussed. (C) 1999 Academic Press.