The Texas Species of Croton (Euphorbiaceae)

Abstract

Key and principal synonymy are given for the 18 accepted Texas species of Croton, and maps are provided to show Texas distribution as indicated by herbarium specimens in several institutions. The species include C. glandulosus L. (3 varieties in Texas: var. septentrionalis Muell. Arg., var. Lindheimeri Muell. Arg., and var. pubentissimus Croizat); C. monanthogynus Michx.; C. leucophyllus Muell. Arg. var. leucophyllus, incl. C. Palmeri S. Wats. (the Mexican variety trisepalis Ferguson is also mentioned); C. corymbulosus Engelm. (var. corymbulosus, and var. thermophilus, new variety); C. Lindheimerianus Scheele (var. Lindheimerianus, and var. Tharpii, new variety); C. capitatus Michx. (var. capitatus, var. Lindheimeri (Engelm. & Gray) Muell. Arg., and var. albinoides (Ferguson) Shinners, incl. C. Muelleri Coulter); C. Coryi Croizat; C. punctatus Jacq.; C. dioicus Cay. (incl. C. neomexicanus Muell. Arg.); C. texensis (Klotzsch) Muell. Arg.; C. Parksii Croizat; C. argyranthemus Michx.; C. ciliatoglandulosus Ort.; C. humilis L.; C. Torreyanus Muell. Arg.; C. suaveolens Torr.; C. Cortesianus H.B.K.; C. fruticulosus Engelm.; lectotypes are designated for several of these names. Croton is a genus of more than 600 species of herbs, shrubs, and trees in warm regions of the world. Perhaps 25 species occur in the United States, staying mainly to the southern states. Texas has 18 of these species, being the richest, in this regard, of the states. The treatment of United States Crotons by Ferguson (1901, repeated largely in Small, 1903) is remarkably well-done. Fortunately most of the original collections of our southwestern species are represented in American herbaria. With vastly greater herbarium stores, opportunities for field study, and full use of a type method, we should now have the basis for a more nearly satisfactory treatment. The following synopsis is based on study of the Crotons at the herbaria of the University of Texas, Southern Methodist University, Sul Ross State College, the United States National Herbarium, and the Academy of Natural Sciences of Philadelphia, and of selected specimens from Gray Herbarium-Arnold Arboretum, and the University of Michigan, and casual examination of the Crotons at the Instituto de Biologia at Chapultepec and the University of California at Berkeley. To the staffs of those herbaria I am grateful for their kindnesses, especially to Dr. C. E. Kobuski, Dr. Lyman B. Smith, and Dr. Lloyd H. Shinners. I am especially grateful to Dr. B. C. Tharp of the University of Texas for his interest.