E. discolor calyces [Jeff Davis Co.].
Sepal form has long been noted as a distinctive characteristic of American Evolvulus species, from Nuttall 1818 on. Within Texas they have received much less attention; e.g., in L. H. Shinners' treatment in the Manual of the Vascular Plants of Texas (1970) only their number, 5, is mentioned. One can speculate that this is due to the ability to distinguish most forms of the Texas taxa east of the Trans–Pecos and north of the Mexican border on the basis of vestiture and flower color. But outside this area, especially in the Trans–Pecos Texas–based treatments and collection determinations in Texas herbaria conflict with more traditional differentia from western states and Mexico (especially as presented in van Ooststroom's 1934 monograph, which nearly everyone cites, but few seem to have actually read).
To get a better perspective of Evolvulus sepal morphology/differences, not easy with pressed specimens which generally present only one side of the 5–sepal calyx, and that often obscured by hairs, I dissected 8 sepals available in collection packets plus several (now dry branches) from my own plants. These were first softened by soaking in hot water and then carefully pried open, pressed flat, and images made of both abaxial and adaxial surfaces. Even with careful handling several sepals broke or ruptured. In general the adaxial surface permitted a better view of sepal structure. The results are shown below. A detailed presentation of the results is given on another page.
