LITERATURE CITED 
Gentry, H.S. 1942. Rio Mayo Plants. Carneg. Inst. Wash. Publ. 
527, 328 pp. 
LeSueur, H. 1945. The ecology of the vegetation of Chihuahua, 
Mexico, north of Parallel Twenty-eight. Univ. Texas Publ. 4521, 
92 pp. 
Mathias, M.E., and L. Constance. 1944-45. Umbelliferae: Fl. N. 
America 28B: 43-295. 
Wolff, H. 1913. Umbelliferae; in Engler, Das Pflanzenreich 61 
(4°"): 1-305, 
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