June through August, plants produce daisy-like flower heads to 1.5 cm across, with lavender rays surrounding yellow discs.

In E. tener, basal leaves are gray green, less hairy, and narrower (2–7 mm); leaf tips are more sharply pointed.

[6] It grows on clay hills, rocky slopes, limestone talus, shale outcrops, and in sagebrush-grasslands, from valleys to subalpine, at 1600–3000 m elevation.

[4][7] Erigeron tweedyi was first collected by Frank Tweedy in 1887, in rocky dry hills along Trail Creek in southwestern Montana.

Canby noted: "It is a peculiar pleasure to give this plant the name of its discoverer, Mr. Frank Tweedy, author of an excellent catalogue of the 'Flora of Yellowstone Park.