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FNA | Family List | FNA Vol. 21 | Asteraceae | Chaenactis

378c. Chaenactis de Candolle sect. Chaenactis

Annuals; proximal indument predominantly arachnoid, lanuginose, stipitate-glandular, or glabrescent, not farinose. Stems mostly 1–5(–12), usually erect to ascending; branches proximal and/or distal. Leaves: largest blades usually ± oblanceolate to elliptic or linear (± ovate in some C. macrantha), (0–)1–2-pinnately lobed, not gland-dotted (except C. macrantha). Heads discoid or ± radiant. Peduncles erect to ascending (by flowering). Phyllaries: outer usually ± blunt, sometimes acute. Florets: corollas white to pinkish, cream, or bright to dark yellow, actinomorphic and ± equal, or peripheral enlarged (and often zygomorphic). Cypselae ± terete (except C. nevii); pappi 0, coroniform (of ± 10 scales), or of (1–)4–8(–14) scales in 1 series, in 2, abruptly unequal series, or in 2–3, gradually unequal series. x = 6.

Species 7 (7 in the flora): sw United States, nw Mexico.

Taxa of sect. Chaenactis grow mainly in valley and foothill habitats; all except Chaenactis macrantha, C. cusickii, and C. nevii appear to form occasional natural hybrids where sympatric. Chaenactis macrantha and C. cusickii may each warrant a separate monotypic section and here probably render sect. Chaenactis polyphyletic. Both species share similarities with C. xantiana.

The species with zygomorphic and enlarged peripheral corollas (Chaenactis glabriuscula, C. stevioides, and C. fremontii) are closely related, and identification of some specimens requires careful evaluation, especially when fresh corolla color is not evident. D. W. Kyhos (1965) presented strong evidence that the species with corollas white and 2n = 10 (C. stevioides and C. fremontii) evolved separately from within C. glabriuscula (corollas yellow, 2n = 12) via chromosomal rearrangements. That study did not sample very well the large amount of variation in C. glabriuscula, nor did it rule out involvement of other taxa such as C. xantiana. Chaenactis xantiana (corollas white, 2n = 14) is known to form hybrids with C. glabriuscula that also exhibit 2n = 10 in some individuals (P. Stockwell 1940).

A series of natural hybrids and backcrosses (keyed below), involving various combinations of the four species named in the preceding paragraph, appears to occur in the inner South Coast Ranges and adjacent southern and western San Joaquin Valley of west-central California. Where Chaenactis xantiana or C. glabriuscula var. heterocarpha is involved, a partial second series of pappus scales is usually evident. Identification of specimens from this area can be difficult.

1 Corollas bright to dark yellow; mainly west of deserts   (2)
+ Corollas white to pinkish, cream, or pale yellow; mainly in and near deserts   (3)
2 (1) Peripheral corollas actinomorphic, scarcely enlarged (relative to inner); cypselae com-pressed; pappi 0 or coroniform (of ± 10 scales, longest 0.1–0.5 mm); Oregon   14 Chaenactis nevii
+ Peripheral corollas ± zygomorphic, enlarged (relative to inner); cypselae ± terete; pappi of (1–)4, or (5–)8, scales, longest scales (1–)2–8 mm; California   15 Chaenactis glabriuscula
3 (1) Peripheral corollas zygomorphic, enlarged; pappi of (1–)4(–5) scales, usually in 1 series (rarely with partial outer series in Chaenactis stevioides); peduncles usually stipitate-glandular distally (at least early, sometimes glabrescent by fruit)   (4)
+ Peripheral corollas actinomorphic, not or scarcely enlarged; pappi of (6–)8–14 scales in 2 abruptly unequal series, or in 2–3 gradually unequal series; peduncles ± arachnoid to lanuginose distally, not stipitate-glandular   (5)
4 (3) Pappi: longest scales 1.5–6 mm, lengths mostly 0.3–0.9 times corollas (apices hidden among corollas at flowering); proximal indument ± arachnoid-sericeous (tardily glabrescent except around nodes); leaf blades mostly 1–2-pinnately lobed, primary lobes mostly 4–8 pairs; outer phyllaries usually stipitate-glandular and/or± arachnoid in fruit, apices blunt   16 Chaenactis stevioides
+ Pappi: longest scales 6–8.5 mm, lengths 1–1.3 times corollas (apices visible among corollas at flowering); proximal indument glabrescent (early ± arachnoid, glabrous by flowering); leaf blades 0–1-pinnately lobed, lobes 1–2(–5) pairs; outer phyllaries usually glabrescent in fruit, apices acute   17 Chaenactis fremontii
5 (3) Corollas (nocturnal) 9–12(–15) mm (lengths 1.8–2.2 times cypselae; anthers ± included); leaf blades not succulent   11 Chaenactis macrantha
+ Corollas (diurnal) 3–10 mm (± equaling cypselae; anthers exserted); leaf blades± succulent   (6)
6 (5) Longest phyllaries 10–18 mm (surpassed by florets), outer distally tomentulose-puberulent in fruit (proximally glabrous), not stipitate-glandular   13 Chaenactis xantiana
+ Longest phyllaries 6–9(–10) mm (or surpassing florets), outer (uniformly) ± arachnoid and/or stipitate-glandular or glabrescent   (7)
7 (6) Pappi of (8–)10–14 scales in 2–3 gradually unequal series; leaf blades ± oblanceolate, not lobed (margins entire or distally ± crenate); peduncles: bracts 1–2, leaflike, surpassing heads; outer phyllaries sparsely arachnoid to glabrescent, not stipitate-glandular (inner apically brownish villosulous)   12 Chaenactis cusickii
+ Pappi of 6–8 scales in 2, abruptly unequal series; leaves mostly ± elliptic, mostly 1–2-pinnately lobed; peduncles: bracts 0 or 1–2 ± subulate, surpassed by heads; outer phyllaries usually stipitate-glandular, other indument various (apices of inner not villosulous) [hybrids among Chaenactis fremontii, C. glabriuscula, C. stevioides, and C. xantiana; see discussion of C. sect. Chaenactis]   (1)

  • List of lower taxa


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