A Systematic Re-Evaluation of Phacelia mohavensis var. exilis (Hydrophyllaceae)

Abstract

Phacelia mohavensis var. mohavensis and P. mohavensis var. exilis are distinct entities that differ in their stamen length; petal, pollen, and filament color; petal shape and orientation; petal venation patterns; and leaf morphology. As consequence of these differences, P. mohavensis var. exilis is considered to be distinct species: P. exilis. Both species have haploid chromosome number of n = 9. Phacelia mohavensis A. Gray is montane an- nual of southern California, ranging from the Greenhorn Mts. of southern Tulare Co. to dis- junct populations in Ventura, Los Angeles, and San Bernardino cos. Asa Gray first described the species and Phacelia mohavensis var. exilis in 1878. Eventually he treated the variety as a slender erect form of the species (Gray 1880), treat- ment subsequently adopted by Howell (1945), Constance (1951), and Munz (1959). My field, greenhouse, and herbarium studies of popula- tions from throughout the range of the two taxa were conducted after initial field observations indicated consistent and substantial morpho- logical differences between the taxa originally described by Asa Gray. This paper re-examines and clarifies their status in light of those dif- ferences.