Flora of North America species comparison

Stephanomeria pauciflora generally grows as an intricately branched, often rounded bush. Occasional plants, usually from Arizona, New Mexico, Texas, and southern Utah, have long, flexuous stems and branches, an architecture that resembles one of the typical forms of S. tenuifolia. Some plants of S. pauciflora have white pappi, also typical of S. tenuifolia. It is not known if these plants represent uncommon and unusual individuals or if they are from populations in which all plants have those traits. It is also not known whether such plants of S. pauciflora grow near populations of S. tenuifolia; if so, they may result from interspecific hybridization. That is a possibility; experimental hybrid plants produced by crossing individuals from the two species were about 20% fertile. Such fertility suggests the species are sufficiently compatible that fully fertile segregants with variously intermediate morphologies could be expected where they hybridize in nature. The experimental crosses were made reciprocally between S. pauciflora from Riverside County, California (L. D. Gottlieb 6653), and S. tenuifolia from Wheeler County, Oregon (L. D. Gottlieb 6692); specimens of the six F1 hybrid plants that were produced are deposited at DAV. Plants of S. pauciflora that are densely tomentose throughout are occasionally found, particularly in the deserts of California and Nevada, and have been named S. cinerea or S. pauciflora var. parishii.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Stephanomeria tenuifolia is distributed over an immense region and is the most widespread species of the genus. It shows remarkable variability in the form and dimensions of its stems and branches. Plants described as S. myrioclada, from the northeasternmost corner of Nevada, present an architecture of relatively numerous, almost threadlike, densely crowded stems (1.5–4 dm) and branches with an irregularly dichotomous pattern. Continuous variation occurs from this form to another in the same region and elsewhere in which the stems are longer (3–7 dm), sparingly branched, and flexuous. The extreme variability in vegetative architecture may be adaptive and deserves further study.

Stephanomeria wrightii was described from western Texas. The type sheet has three specimens, all with a single, slender stem with paniculately disposed branches from a broken-off stub. A. Gray (1884, 1886) stated that those features indicated the plants were “seemingly biennial,” and distinguished them from S. minor Nuttall (an old synonym of S. tenuifolia), which he said has “thick and tortuous roots.” The slender stem of the specimens received by Gray may indicate their young age; they do not seem distinctive because other specimens from the same region have the bright white, fully plumose pappi and other features ascribed to S. wrightii, but also exhibit large, thick rhizomes. Gray noted that the “achenes are contracted under the summit”; this feature is not evident on the three specimens. Overall, S. wrightii does not seem different from S. tenuifolia.

The type specimen of Stephanomeria neomexicana, originally described as Ptiloria neomexicana by E. L. Greene, from New Mexico, exhibits multiple, long, flexuous stems with relatively few branches emerging from a stout rhizome. The pappi consist of plumose bristles, but the proximal 0.5–l mm is only minutely barbed. Plants with similar pappi are found occasionally in New Mexico and Arizona and differ in no other respect from S. tenuifolia.

Stephanomeria tenuifolia var. uintaensis grows “in one small isolated stand” (S. Goodrich and S. L. Welsh 1983) and was recognized primarily on the basis of relatively long phyllaries (10–16 mm) and runcinate-pinnatifid basal leaves. I measured phyllary lengths on isotypes; only one, from a terminal head, was 16 mm; others varied from 11–14(–15) mm. Although the lengths are 2–3 mm longer than typical, no other feature of the plants is unusual. Pinnately lobed leaves may not be typical of the species; because leaves are not often present on S. tenuifolia when it is in flower, and most specimens do not include them, the significance of the character is uncertain. The isotype collections are from young individuals and only the paratype from RM has cypselae. The variety does not seem worthy of taxonomic recognition.

(Discussion copyrighted by Flora of North America; reprinted with permission.)