Heterotheca

Prairie and Montane Goldenasters and Telegraph Weeds

Heterotheca SEM hairs

Heterotheca Cassini includes all the goldenasters that have leaf hairs consisting of bone-shaped (osteolate) cells with knobbed surfaces.      The genus is divided into three sections based on fruit characteristics, presence or absence of ray florets, and growth form. Species of Heterotheca are native to southwestern Canada, much of the U.S. and most of Mexico.

Distribution of Heterotheca in North America

Heterotheca sect. Heterotheca

Heterotheca sect. Heterotheca includes three species with heterocarpic heads (two kinds of fruit; e.g., H. subaxillaris). The two species native to the U.S. are weedy annuals sometimes reaching 2 m in height, but can be short lived perennials in Mexico.

Heterotheca sect. Ammodia

Heterotheca sect. Ammodia (Nutt.) Harms includes one species H. oregona with four varieties native to gravel bars and arroyos from Washington to Central California. The species has rayless heads.

Heterotheca sect. Phyllotheca

Heterotheca sect. Phyllotheca (Nutt.) Harms (Semple et al. 1980, Semple 1996, 2006) includes 20 species of mostly herbaceous perennials ranging in height from a few cm (H. jonesii) to more than 1.2 m (H. shevockii) that were historically, but incorrectly, placed in Chrysopsis (Semple 1977, Semple et al. 1980, Semple 2006).  The ray and disc fruits are similar and the leaf and stem hairs are like those of H. sect. Heterotheca; the cells are osteolate with knobby surfaces. Cronquist (1996) continued to include species of sect. Phyllotheca in his treatment of the goldenasters in the Flora of the Great Basin. Most species are usually 10-50 cm tall (e.g., H. pumila). Many species are restricted to particular soil types or habitats (e.g., H. brandegei, Baha CA Norte; H. monarchensis, CA; a few species are widely distributed (e.g., H. villosa; nine varieties). Species are defined by different combinations of leaf traits (size, shape, numbers of hairs and glands), head features (size, numbers of florets) and habit (growth form) features. All line drawing illustrations are from Semple (1996) and are © J.C. Semple (1996). Nesom (2019, 2020) treated this group as a large sect. Chrysanthe and a small sect. Phyllotheca and recognized 49 species splitting up H. villosa into 14 new species and raise many varieties to species level. This is a classic cases of lumpers vs. splitters.

Molecular data subsequently supported the generic limits followed here rather than the traditional limits Cronquist accepted throughout his life (Brouillet et al. 2009).  Heterotheca sensu Semple grouped with Croptilon and Noticastrum in one clade, while Chrysopis grouped with Braduria in a second clade, and Pityopsis came out as a polytomy at the base of the Chrysopsidinae Clade.  Further work is needed.

Nesom (2019, 2020) restricted sect. Phyllotheca to just the California H.sessiflora complex with longer hairs on the corolla lobes and included 49 species in  his H. sect. Chrysanthe Nesom (2019, 2020) with no hairs or short hairs on the corolla lobes, athough I my opinion his diagnosis for the section is not adequate to delineate the two sections.  Nesom (2020) described 14 new species and raised those taxa listed below as varieties to species level.  Splitting up some of the multi-varities species into multiple species can be justified for a number of reasons. Some of his new species are narrow endemics that I might have treated as species in 1996 and 2006 had they been known at that time. Whether all the splitting proposed by Nesom is justified will need data from polygenomic studies to determine what taxa are closely related and which stand off by themselves. A polygenomic study of the entire genus with multiple samples of every possible taxon is a very large task that is doable with sufficient funding potentially using only recently collected herbarium samples. Marisa Szubryt   (marisabszubryt@gmail.com, marisabszubryt@ou.edu) has kindly sent me a preliminary molecular phylogeny of Heterotheca that will be refined as part of her on going doctoral thesis reseach.  Such data are not currently published and readers must decide for themselves to be a "lumper" or a "splitter".  Species are listed below in alphabetic order out of necessity at this time. Nesom's numerous species names are noted in the linked web pages for each of the species listed below.

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].

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.

Semple, J.C., V. Blok and P. Heiman. 1980. Morphological, anatomical, habit, and habitat differences among the goldenaster genera Chrysopsis, Heterotheca and Pityopsis (Compositae- Astereae). Can. J. Bot. 58: 147-163.

Last revised 25 April 2025 by J.C. Semple

© 2025 J.C. Semple, including all photographs unless otherwise indicated