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FNA | Family List | FNA Vol. 20 | Asteraceae | Xanthisma

3. Xanthisma coloradoense (A. Gray) D. R. Morgan & R. L. Hartman, Sida. 20: 1403. 2003.

Aster coloradoensis A. Gray, Proc. Amer. Acad. Arts 11: 76. 1876; Haplopappus coloradoensis (A. Gray) R. L. Hartman ex Dorn; Machaeranthera coloradoensis (A. Gray) Osterhout; M. coloradoensis var. brandegeei (Rydberg) T. J. Watson ex R. L. Hartman; Xylorhiza brandegeei Rydberg

Perennials, 2.5–14 cm; caudices branched; taproots 3–13+ cm. Stems 8–30+, simple, moderately stout to stout, not wiry, villous to pilose. Leaves: basal persistent (similar to cauline); cauline only a few pairs clustered with basal, absent distally, blades narrowly to broadly oblanceolate or spatulate, 10–80 × 3–10 mm, margins evenly to irregularly serrate or serrulate, teeth 3–14 per side, each tipped with white bristle 0.5–2 mm, faces sparsely to moderately hairy. Heads 1. Peduncles moderately to densely white-puberulent, eglandular; ebracteate. Involucres depressed-hemispheric, 5–8 × 10–25 mm. Phyllaries in 3–4 series, broadly linear to lanceolate, 2.5–13 mm, apices acute to acuminate, tipped by white seta, faces moderately puberulent. Ray florets 20–35; corollas pink to purple, tubes 2–3.5 mm, laminae 9.3–15 × 2.2–4.3 mm. Disc florets 50–150+; 4.5–6.5 mm. Cypselae narrowly obovoid to oblong, 1.7–3 mm, weakly 10–20-nerved or -ribbed, moderately to densely covered with whitish to tawny hairs; pappi whitish to tawny, 3.5–6 mm, a few abaxial bristles to 1 / 3 of longest. 2n = 8, 16.

Flowering summer. Volcanic ash deposits, gravelly soil, limestone outcrops, mountain summits and slopes, occasionally on plains; 2100–3700 m; Colo., Wyo.

Xanthisma coloradoense is mostly alpine, but sometimes present in foothills or on plains, scattered through the southern Rocky Mountains of Colorado and southern Wyoming.

Xanthisma coloradoense and X. grindelioides var. grindelioides are known to hybridize in Carbon County, Wyoming, one of the few places where the two are sympatric. Several hybrid swarms have been detected in the vicinity of Wheatland Reservoir number 2.

Two varieties of Xanthisma coloradoense were recognized by R. L. Hartman (1976, 1990). They were distinguished by size, shape, and serration of leaves, size of flowering heads, and ray corolla length. With the number of additional collections amassed, these distinctions no longer hold and the varieties are not recognized.


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