Bot. Gaz.37: 262. 1904
w North America.
Species 4 (4 in the flora).
Recent work by L. Brouillet et al. (2004) and R. P. Roberts and L. E. Urbatsch (2004) has refined our understanding of the affinities of taxa included by G. L. Nesom and D. R. Morgan (1990) in Tonestus, some of which are now referred to Eurybia, Lorandersonia, or Toiyabea. In spite of these revisions, Tonestus appears to comprise at least three distinct elements. Two species primarily of the Rocky Mountains and ranges of the Pacific Northwest, T. lyallii and T. pygmaeus, resemble one another morphologically; molecular systematic studies by Roberts and Urbatsch suggested that these may be more closely related to different elements of the Solidagininae than they are to each other or to the remainder of the taxa included here in Tonestus. Likewise, while morphologic evidence indicates that T. eximius and T. peirsonii are closely related, the work of Roberts and Urbatsch placed the decaploid T. peirsonii in a clade with members of Lorandersonia wherein it is treated here; T. eximius is placed within a largely unresolved clade of the Solidagininae. Tonestus graniticus is included here mostly as a matter of convenience. It bears only superficial resemblance to other taxa included in the genus, differing in habit, array of heads, involucre, and hair type. The placement of this species within Solidagininae remains uncertain, although the work of Roberts and Urbatsch suggested that it may be related to Chrysothamnus. The treatment presented here must be considered tentative, at best. Tonestus pygmaeus is the nomenclatural type of the genus; further refinement of the taxonomy of this difficult group may require nomenclatural innovations.
|1||Leaf margins entire; Rocky Mountains, ranges of the Pacific Northwest, rarely ranges of n California and nw Nevada||> 2|
|1||Leaf margins serrate, dentate, or lobed; s Great Basin or Sierra Nevada ranges||> 3|
|2||Plants densely stipitate-glandular, otherwise glabrous; outer phyllaries oblong to broadly lanceolate, apices acute; cypselae glabrous or sparsely hairy distally||Tonestus lyallii|
|2||Plants eglandular or sparsely stipitate-glandular, non-glandular hairs present at least as cilia on leaves and phyllaries; outer phyllaries ovate to oblong, apices obtuse or rounded; cypselae villous||Tonestus pygmaeus|
|3||Leaves glabrous; heads radiate, 1 or 2(–4); involucres (9–)12–25(–28) × (5–)8–20 mm; ec California, Washoe County, Nevada||Tonestus eximius|
|3||Leaves scabrous; heads discoid, (1–)3–7(–11); involucres 5–9 × 6–10 mm; Esmeralda County, Nevada||Tonestus graniticus|