Xanthisma
in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 5: 94. 1836.
Annuals, biennials, perennials, or subshrubs, 3–100 cm (taprooted, caudices woody, much branched [rhizomes]). Stems erect, spreading, or sprawling, often much branched, glabrous or hispid to hispidulous, villous, or stipitate-glandular (especially distally). Leaves: basal (sometimes persistent) and cauline; short-petiolate or sessile; blades 1-nerved, lanceolate to oblanceolate or spatulate (bases tapering to clasping), margins entire, serrate, dentate, pinnatifid, or 2-pinnatifid (apices of blades, lobes, and teeth apiculate to bristle-tipped, bristles 1–4 mm), faces usually glabrous, hispid, hispidulous, or villous, sometimes also stipitate-glandular. Heads radiate or discoid, borne singly or in corymbiform arrays. Involucres turbinate, campanulate, or hemispheric, (4–10 ×) 6–25 mm. Phyllaries 26–80+ in 2–8 series, appressed, spreading, or reflexed, 1-nerved (flat to rounded), linear to narrowly oblong or lanceolate, or enlarged distally into ovate to orbiculate or depressed-elliptic laminae, unequal, stiff, leathery, bases indurate, margins sometimes scarious, (apices herbaceous or achlorophyllous) faces hispid to hispidulous, villous, and/or stipitate-glandular. Receptacles flat to convex, pitted (pit borders usually laciniate or irregularly bristly, the teeth or setae 0.1–2+ mm), epaleate. Ray-florets 0 (in X. grindelioides and 2 Mexican taxa) or 12–60+, pistillate, fertile; corollas white, pink, red-purple, purple, or yellow. Disc-florets 15–200+, bisexual, fertile; corollas yellow, tubes length 1/4–1/3 ± funnelform throats (usually glabrous), lobes 5, spreading, triangular (glabrous or sparsely puberulent, hairs fine, antrorse); style-branch appendages lanceolate. Cypselae distinctly dimorphic (tan to redbrown or purple), ellipsoid to obovoid, oblong, or obscurely cordate, those of rays (if present) ± 3-sided, rounded abaxially, of disc compressed (thin or thick walled), 6–18-ribbed, faces silky (hairs antrorsely ascending to appressed); pappi persistent, of 30–90+ usually whitish to brown or reddish-brown, basally flattened (wider at overlapping bases), coarsely barbellate, apically attenuate bristles in 2–4 series. x = (2, 3, 4) 5.
Distribution
w North America, Mexico
Discussion
Species 17 (9 in the flora).
As here circumscribed, Xanthisma includes four sections of Machaeranthera in the sense of R. L. Hartman 1990: Blepharodon, Sideranthus, Havardii, and Stenoloba. The last section, consisting of a single Mexican species, is treated here as a synonym of sect. Sideranthus. This grouping is well supported by molecular data (D. R. Morgan 1993, 1997, 2003; Morgan and Hartman 2003; Morgan and B. B. Simpson 1992). Although Xanthisma includes species with both cyanic (blue, purple, pink, or white) and yellow rays, several morphologic characteristics are shared by its members, including short, turbinate, thick-walled fruits that are moderately to densely silky, receptacular scales, leaves with marginal spines, and chromosome numbers based on x = 4 or 5, with a descending dysploid series in one taxon. Many of these species have, in fact, been grouped together at the generic or sectional level by earlier authors such as E. L. Greene (1894b), H. M. Hall (1928), L. H. Shinners (1950b), A. Cronquist and D. D. Keck (1957), J. C. Semple (1974), and Hartman (1976, 1990). The following key is based largely on data from Hartman (1976, 1990) and Semple.
Selected References
None.
Lower Taxa
Key
| 1 | Inner phyllaries (at least) with proximal portion stalklike, abruptly enlarged into ovate to orbiculate or elliptic blade, 2–5 mm wide, apices acuminate to obtuse or broadly rounded, not bristle-tipped (Texas, s Oklahoma, e New Mexico) (sect. Xanthisma) | Xanthisma texanum |
| 1 | Phyllaries not markedly expanded distally, linear to broadly oblong or lanceolate, 1–2 mm wide, apices narrowly obtuse to long-attenuate, usually bristle-tipped | > 2 |
| 2 | Rays white, pink, purple, or lavender, or ray florets 0 (sect. Blepharodon) | > 3 |
| 2 | Rays yellow | > 6 |
| 3 | Ray florets 0 (n New Mexico and n Arizona to sw Canada) | Xanthisma grindelioides |
| 3 | Ray florets present | > 4 |
| 4 | Plants 2.5–14 cm; stems simple; basal leaves (rosettes) persistent; heads 1; (montane to alpine) Colorado, s Wyoming | Xanthisma coloradoense |
| 4 | Plants 15–40 cm; stems often branched distally; basal leaves usually withering by flowering; heads 1–10+; s New Mexico, w Texas, n Mexico | > 5 |
| 5 | Leaves usually finely or obscurely serrate or serrulate, usually with 12–25 teeth per side; peduncles hispid or hispidulous; s New Mexico, w Texas | Xanthisma blephariphyllum |
| 5 | Leaves serrate, often coarsely, with 5–14 teeth per side; peduncles stipitate-glandular; se New Mexico and w Texas; n Mexico | Xanthisma gypsophilum |
| 6 | Annuals, taprooted; leaves serrate to dentate, teeth blunt or terminating in a stiff callosity, not bristle-tipped; phyllary apices obtuse to broadly acute, not bristle-tipped; cypselae oblong or narrowly ellipsoid, 18–22-nerved (barely discernible); se New Mexico, w Texas (sect. Havardii) | Xanthisma viscidum |
| 6 | Perennials or subshrubs with branched caudices (if taprooted annuals then phyllary apices narrowly acute to acuminate, prominently bristle-tipped); leaves entire, pinnatifid, or deeply 2-pinnatifid, if serrate or dentate, teeth bristle-tipped; cypselae ellipsoid to broadly obovoid, ribs weak yet readily discernible; w North America, Mexico (sect. Sideranthus) | > 7 |
| 7 | Annuals, taprooted | Xanthisma gracile |
| 7 | Perennials or subshrubs, caudices branched, often woody | > 8 |
| 8 | Cauline leaves scalelike throughout; peduncle bracts imbricate, grading into phyllaries | Xanthisma junceum |
| 8 | Cauline leaves not scalelike at least proximal to midstems; peduncle bracts 0–3, leaflike, not grading into phyllaries | Xanthisma spinulosum |
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