A revision of Heterotheca sect. Phyllotheca (Nutt.) Harms

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

Abstract

The goldenasters are members of a related group of North and South American genera: Bradburia, Chrysopsis, Heterotheca, Noticastrum, Osbertia, Pityopsis and Tomentaurum. Heterotheca is the largest of these and includes 28 species in three sections distributed from southern Mexico to southwestern Canada and nearly all of the United States except Alaska. All members of the genus Heterotheca have uniseriate osteoform hairs with pusticulate surfaces. The largest and most widely distributed section is monographed in this revision. Heterotheca sect. Phyllotheca includes 20 species and 24 varieties of prairie and montane goldenasters. In the type species of the section H. sessiliflora, the varieties are grouped into four subspecies. There is a recurring pattern to morphological variation within most species based on variation in leaf indument. At one extreme are species and varieties with many to very many hairs and few or no glands; e.g. H. canescens, H. fulcrata var. amplifolia, H. gypsophila, H. sessiliflora var. fastigiata, and forms of H. villosa var. pedunculata. At the other extreme are the races with relatively few hairs and comparatively many glands; e.g., H. fulcrata var. arizonica, H. mucronata var. harmsiana, H. sessiliflora var. camphorata, and H. villosa var. nana. Taxa can also be separated on the basis of differences in leaf shape, stem height, capitulescence form, or the presence or absence of one or more large leaf-like bracts subtending the heads. Generally, combinations of traits define taxa rather than single distinctive features. There are habitat preference differences that also help define taxa, but the ranges of many varieties and species overlap considerably. Nearly all taxa have ranges that differ from those of related taxa. The genus has a chromosomal base number of x = 9. Many species include both diploids and tetraploids, while some are known only at the diploid or only at the tetraploid level.

A table summarizing the traits of all genera that have been included in the goldenaster group is presented along with range maps of each genus in North or South America.

A key to all taxa in the genus Heterotheca is included.

All taxa in sect. Phyllotheca are illustrated in detail, and dot distribution maps based on all collections seen are included for each taxon in the section.

The following new names and combinations are proposed: Bradburia pilosa (p.7) Heterotheca fulcrata var. amplifolia (p.74), H. marginata (p.83), H. monarchensis (p.52), H. mucronata var. harmsiana (p.60), H. shevockii (p.148), and H. villosa var. sierrablancensis (p.147).
 

Sample Figure: Heterotheca marginata Semple