Amer. J. Bot. 83: 368. 1996
Annuals to perennials, 4–80 cm, herbage glabrous, prominently sessile- to stipitate-glandular; taprooted. Stems erect to decumbent-ascending, branched basally (leafy throughout). Leaves mostly cauline; alternate; sessile to subpetiolate; blades 1-nerved (pinnately veined), linear to oblanceolate, margins coarsely serrate (teeth bristle-tipped), rarely entire (apices acute to obtuse). Heads radiate, in paniculiform or subcorymbo-cymiform arrays. (Peduncles sometimes cobwebby.) Involucres hemispheric, (7–16 ×) 9–30 mm. Phyllaries 20–40 in 4–5 series, appressed or tips spreading to reflexed, 1-nerved (flat or proximally convex), linear to lanceolate or ovate-lanceolate, equal to subequal, white-indurate, margins of inner scarious (apices erect, loosely spreading, or recurved, green-herbaceous, acute to acuminate), faces glabrous or glandular. Receptacles shallowly convex, pitted, epaleate. Ray florets 14–46, pistillate, fertile; corollas yellow. Disc florets 25–130, bisexual, fertile; corollas yellow, tubes shorter than abruptly ampliate throats, lobes 5, erect, triangular; style-branch appendages deltate. Cypselae dimorphic, faces strigoso-sericeous; ray broadly ellipsoid to obovoid, 3-angled (thick-walled), 0–4-ribbed; disc broadly ellipsoid to clavate, ± radially compressed (thinner-walled), 5–9-ribbed; pappi persistent, of 30–40 brownish, unequal, barbellate, attenuate bristles in 3–4 series (about as long as disc corollas), outer thinner, terete, inner thick-flattened. x = 6.
s, c, se United States, n Mexico.
Species 3 (3 in the flora).
R. L. Hartman (1990) informally recognized the three species of Rayjacksonia as an undescribed genus most closely related to Grindelia, Isocoma, Xanthocephalum, and other genera of Machaerantherinae with x = 6. The taxonomy was formalized by M. A. Lane and Hartman (1996). The Rayjacksonia species are coherent in vestiture, spinulose leaf teeth, heads borne singly, and rays with prominent, yellow laminae.
|1||Mid-cauline leaf blades linear to linear-oblanceolate, 1–3(–4) mm wide; involucres 4–7 × 10–15 mm; rays 14–19, corollas 6.5–9.5 mm||Rayjacksonia aurea|
|1||Mid-cauline leaf blades oblanceolate to oblong or oblong-lanceolate, (1–)4–15(–25) mm wide; involucres (4.5–)6–15 × 9–30 mm; rays (13–)17–38, corollas 6–19 mm||> 2|
|2||Heads on short, leafless or bracteate peduncles, not surpassed by distal leaves; mid-cauline leaf blades (1–)4–15(–25) mm wide; phyllaries in 3–4 series, strongly unequal, apices broadly spreading to squarrose, ca. 0.9–1 mm wide||Rayjacksonia annua|
|2||Heads essentially sessile, often surpassed by distal leaves that continue to very base of heads; mid-cauline leaf blades (2.5–)4–13 mm wide; phyllaries in 3–4 series, subequal, apices erect to spreading, 1.3–1.7 mm wide||Rayjacksonia phyllocephala|