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.
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.
This project was made possible in part by the Institute of Museum and Library Services [MG-70-19-0057-19].