During a walk at the lake in mid-September, a plenitude of poetic purple purveyed by nature surrounded me at every turn, for purple bindweed (a.k.a. cotton morning glories; Ipomoea trichocarpa) grew in abundance.
[note that I’ve also seen this perennial native of Texas identified as Ipomoea cordatotriloba var. torreyana; the closest I can come to that is from Texas A&M University; they label the species as Ipomoea trichocarpa Ell. var. Torreyana]