Isocoma
goldenbush, goldenweed, jimmyweed
usually strictly erect, few-branched, glabrous or hispidulous, villous, or tomentose, usually gland-dotted (sessile or slightly sunken in pits), sometimes stipitate-glandular, rarely eglandular, often resinous.
mostly cauline; alternate;
sessile;
blades 1-nerved, linear to oblanceolate or obovate, margins entire or toothed to pinnatifid (teeth or lobes often spinulose-tipped), faces glabrous or hispidulous, villous, or tomentose, usually gland-dotted (in pits).
obconic to turbinate or campanulate, (3–9.5 ×) 2–8 mm.
flat, pitted, epaleate.
8–34, bisexual, fertile;
corollas yellow with dark orange-resinous veins, tubes (with at least a few glandular hairs) longer than abruptly ampliate, goblet-shaped throats (tube elevating corollas above involucres at flowering), lobes 5, erect, deltate (elongating at maturity, unequal, outer prominently bent or leaning outward, abruptly enlarged);
style-branch appendages narrowly triangular.
15–30 in (3–)4–6 series, 1-nerved (midnerves usually barely evident; flat to convex), oblong- to elliptic-lanceolate, unequal, margins narrowly scarious, apices sometimes green, faces glabrous or tomentose, sometimes gland-dotted, sometimes with resin pockets.
discoid, (sessile or subsessile) in compact clusters borne in terminal corymbiform arrays, rarely borne singly.
(brownish) obpyramidal, terete or subterete, 5–11-ribbed (sometimes thick and resinous), faces sericeous;
pappi persistent, of 40–50 unevenly thick, unequal, barbellate, apically attenuate bristles in 2(–3) series.
= 6.
Isocoma
Species 16 (10 in the flora).
Isocoma is recognized by its subshrubby habit, gland-dotted (sometimes stipitate-glandular), often resinous leaves, compactly clustered discoid heads in terminal, corymbiform arrays, goblet-shaped disc corollas, and base chromosome number of x = 6. H. M. Hall (1928) regarded the group as a section of Haplopappus, as did A. Cronquist (1994). Naturally occurring hybrids in south-central Mexico have been observed between Isocoma veneta (Kunth) Greene and Xanthocephalum humile (Kunth) Bentham (R. L. Hartman and M. A. Lane 1991).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Phyllary apices with strongly developed resin pockets | → 2 |
1. Phyllary apices gland-dotted (rarely so in I. coronopifolia), lacking resin pockets or pockets small, weakly developed | → 3 |
2. Teeth or lobes of leaf margins apically rounded-obtuse; florets 8–27; phyllary apices not spinulose-aristate, or if spinulose-aristate, then florets 20–27 | I. acradenia |
2. Teeth or lobes of leaf margins apically spinulose; florets 10–13; phyllary apices spinulose-aristate | I. arguta |
3. Leaves pinnatifid | → 4 |
3. Leaves entire or shallowly toothed to lobed, not pinnatifid | → 6 |
4. Herbage minutely hispidulous or sparsely puberulous (at least distal stems) | I. tenuisecta |
4. Herbage glabrous | → 5 |
5. Involucres 5–7.5 mm wide; florets 18–25 | I. azteca |
5. Involucres 2.5–4 mm wide; florets 12–15 | I. coronopifolia |
6. Phyllary apices distinctly aristate-spinulose; florets 10–13; California | I. arguta |
6. Phyllary apices not aristate-spinulose; florets 8–34; California and eastward | → 7 |
7. Involucres 3.2–7 × 2.5–4 mm; florets 8–17(–21) | → 8 |
7. Involucres 5–9 × 4.5–8 mm; florets (15–)18–34 | → 9 |
8. Leaves never stipitate-glandular but almost always resinous, glabrous; involucres 5–7 mm | I. coronopifolia |
8. Leaves sometimes stipitate-glandular, never resinous, margins hispidulous, sometimes also on faces; involucres 3.2–5.5 mm | I. pluriflora |
9. Leaves 5–10(–18) mm; corollas 4–5 mm | I. humilis |
9. Leaves (in I. menziesii 5–)13–50 mm; corollas 5–7.5 mm | → 10 |
10. Leaf margins entire or toothed to lobed; California | I. menziesii |
10. Leaf margins entire; e of California | → 11 |
11. Involucres (5.5–)6–9.5 × 5–7.5 mm; phyllary apices yellowish to greenish yellow, sparsely or not at all gland-dotted; florets 19–25, corollas 5–6.5 mm; cypsela ribs forming hornlike extensions; Arizona, Colorado, New Mexico, Utah | I. rusbyi |
11. Involucres (5.5–)6.5–8 × 4.5–5.5(–7) mm; phyllary apices usually green, usually densely gland-dotted; florets (18–)22–34, corollas 5.8–7.5 mm; cypsela ribs not forming hornlike extensions; Texas | I. drummondii |
CA
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