Ayers, Johnson & Ayers, 2022

Diastatea subg. Angustifolia E.P.Johnson and T.J. Ayers , subg. nov. TYPE: Diastatea tenera (A.Gray) McVaugh, Bull. Torrey Bot. View in CoL Club 67: 143. 1940.

Middle and upper cauline leaves narrowly elliptic to linear, glabrous. Corolla tube cylindric or with gibbous projection at base.

Distribution —The southern range limit of Diastatea subg. Angustifolia is in central Guerrero ( Fig. 7 View FIG ). The subgenus has a center of distribution across the Trans-Mexican Volcanic Belt mostly from Jalisco to Puebla, but there are also populations of the most widespread species, D. tenera , near the edge of the Central Mexican Plateau from Zacatecas to Durango with outliers in Sonora and Oaxaca. The disjunct population of D. tenera in Sonora may be derived from the Jalisco population as suggested by its placement in the phylogeny.