FLOWERING PLANTS AND FERNS OF ARIZONA 743 



Key to the species 



1. Plant entirely glabrous, very succulent 3. H. curassavicum. 



1. Plant evidently hairy, not succulent (2). 



2. Corolla 8 to 15 mm. wide, with a long-exserted tube; style elongate, many 



times longer than the stigma 1. H. convolvulaceum. 



2. Corolla 2 to 4 mm. wide, usually with an included tube; style short, about 

 as long as the stigma 2. H. phyllostachyum. 



1. Heliotropium convolvulaceum (Nutt.) A. Gray, Amer. Acad. Arts 



and Sci. Mem. ser. 2, 6: 403. 1859. 



Euploca convolvulacea Nutt., Amer. Phil. Soc. Trans, ser. 2, 5: 

 189. 1837. 



Northeastern Arizona, southward along the Little Colorado River 

 to near Holbrook, 4,500 to 6,000 (?) feet, dry sandy places. Nebraska 

 to Texas, southern Utah, Arizona, and Mexico. 



The corollas are very attractive, being large, pure white, and sweet- 

 scented, opening in the late afternoon. The distribution in Arizona, as 

 given above, is that of the typical form, with stems and leaves closely 

 strigose. The var. calijornicum (Greene) Johnston (H. californicum 

 Greene), a well-marked western variant with spreading pungent 

 bristles on the stems and leaves, occurs in similar situations but at 

 lower altitudes and under drier conditions at Beaver Dam (Mohave 

 County) and near Yuma, also in adjacent California and Sonora. 



2. Heliotropium phyllostachyum Torr., U. S. and Mex. Bound. Bot. 



137. 1859. 



Mountains of southeastern Arizona (Pinal, Santa Cruz, and Cochise 

 Counties), 4,000 to 5,000 feet, sands and gravel, frequently near 

 streams, type from near Santa Cruz, Sonora. Southern Arizona, 

 Sonora, and Baja California. 



As originally described the species was a complex. The original 

 suite of specimens represents 3 different species. 



3. Heliotropium curassavicum L., Sp. PL 130. 1753. 



Valleys of the Little Colorado, Colorado, and Virgin Rivers (Coco- 

 nino, Mohave, and Yuma Counties), eastward in the valley of the Gila 

 River to Pinal County, moist saline soil. The species is widely dis- 

 tributed in the warmer parts of the Western Hemisphere. 



The distribution in Arizona, as given above, is that of var. oculatum 

 (Heller) Johnston (H. oculatum Heller) , with the corolla 3 to 5 (rarely 

 7) mm. wide, usually becoming distinctly purple or purplish at the 

 throat, and the fruit 1.5 to 2 mm. wide. This variety ranges from 

 southwestern Utah to Baja California. The var. obouatum DC. (H. 

 spathulatum Rydb.), with the corolla 5 to 10 mm. wide, at most only 

 purplish-tinged at the throat, and the fruit 2.5 mm. wide, has been 

 collected in and near the valley of the Little Colorado River, at 

 Holbrook and Tuba, and ranges from Iowa, southwestward to Chihua- 

 hua and Arizona, northwestward to Saskatchewan and Washington. 

 It intergrades northward with var. oculatum, but apparently remains 

 distinct in Arizona. Typical H. curassavicum (H. xerophUum Cock- 

 erell), widely distributed in the American tropics and extending north- 

 ward, to New Mexico, is a more slender, less glaucous plant than var. 



