Heterotheca villosa (Pursh) Shinners is includes a complex assemblage of morphotypes, some nearly allopatric ranges and others with mostly overlapping ranges.  Races are distinguished on the basis of leaf shape, hair density and gland density.  Most races occur at both the 2x and 4x level which increases the ranges of morphological variation. Numerous intermediates occur between the varieties listed below following Semple (1996, 2006).  Alternative classifications have been published by Cronquist and Nesom in regional floristic treatments and by others over multiple decades. Nesom (2020) divided the species into numerous more narrowly distributed taxa and split his sect. Chrysanthe into 49 species in total.  No key to the species was provided.  Nesom (2019) limited sect. Phyllotheca to just the H. sessiliflora complex.  Nesom (2020) split var. minor into multiple species that I consider would be difficult to separate into multiple varieties that integrade.  Species level recognition is unreasonable without significant molecular or morphometric analyses to support the splitting.  Some of Nesom's species might warrant recognition at some level but a lot of work is needed to determine which.

Semple, J.C. 1996. A revision of Heterotheca sect. Phyllotheca (Nutt.) Harms (Compositae: Astereae): the prairie and montane goldenasters of North America. U.Waterloo Biol. Series No. 37: 1-164.

Semple, J.C. 2006.  Heterotheca Cassini. pp. 230-256. In Flora North America Editorial Committee, eds. Flora of North America. Vol. 20. Asteraceae, Part 2. Astereae and Senecioneae. Oxford University Press, New York.

Nesom, G.L. 2019. Taxonomic summary of Heterotheca (Asteraceae: Astereae): Part 1, sects. Heterotheca and Ammodia. Phytoneuron 2019-64: 1–44.

Nesom, G.L. 2020. Taxonomic summary of Heterotheca (Asteraceae: Astereae): Sect. Chrysanthe. Phytoneuron 2020-68: 1–
359 [in 5 parts: 1–74; 75–134; 135-216; 217–319; 320–359].

Last update 19 May 2023 by J.C. Semple

© 2023 J.C. Semple, including all photographs unless otherwise indicated