[Wikipedia] Similarity to Other Species, Taxonomy, Description, Range: It is similar to Cucurbita californica, Cucurbita cordata, Cucurbita cylindrata, and Cucurbita digitata and all these species hybridize readily.[3] It was first identified by Sereno Watson in 1876.[1] These species form the only restricted xerophyte species group in the genus Cucurbita. Each member of this species group is native to the Southwestern United States and Northwestern Mexico where they are relatively uncommon. Each group member is found in hot, arid regions with low rainfall. They prefer soil that is loose, gravelly, and well-drained. C. palmata is native to northeastern Baja California, southeastern California, and southwestern Arizona to a point near the Colorado River. The juvenile leaves of C. cylindrata, C. cordata, C. digitata, and C. palmata show a high degree of similarity, but their mature leaves are visibly different, as are their root structures. (link added by Mary Ann Machi)