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Tetradymia nuttallii Torr. & Gray (Nuttall horsebrush) . . 61 



Tetradymia spiaosa Hook. & Arn. (spiny horsebrush) ... 62 



CHARACTERISTICS OF THE GENUS XANTHOCEPHALUM 



(MATCHBRUSH, SNAKEWEED) 63 



Xanthocephalum microcephala Shinners (small headed 



matchweed) 64 



Xanthocephalum sarothrae Shinners (broom snakeweed). . . 64 



LITERATURE CITED 66 



APPENDIX 73 



Compositae — Key to genera and species 73 



