Pittonia 3: 45. 1896
Perennials, 5–30 cm (taproots deep, woody, usually with 1–2 horizontal, spreading, sprouting branch roots, and root crowns bearing woody, branched caudices). Stems erect, simple or branched, glabrous or sparsely tomentose. Leaves mostly cauline (crowded); alternate; sessile; blades 1- or weakly 3-nerved, linear to narrowly oblanceolate or lanceolate (little reduced to immediately proximal to heads), margins entire, faces glabrous or sparsely villous. Heads radiate or discoid, borne singly or (2–12) in loose corymbiform or nearly glomerate arrays. Involucres hemispheric to campanulate or cylindro-turbinate, 7–25 × 5–20 mm. Phyllaries 20–35 in 3–6 series, 1-nerved (sometimes weakly keeled by thin, indurate midnerves), ovate-triangular to oblong-lanceolate, unequal to subequal, outer herbaceous, inner chartaceous, margins not scarious, flat to convex (apices long-acuminate to abruptly obtuse and cuspidate or apiculate), faces glabrous or puberulent. Receptacles shallowly convex, barely pitted, epaleate. Ray florets 0 or 6–25, pistillate, fertile; corollas yellow. Disc florets 15–50, bisexual, fertile; corollas yellow, tubes shorter than funnelform throats, lobes 5, erect, deltate to triangular; style-branch appendages triangular. Cypselae (brownish) prismatic or narrowly turbinate, slightly compressed to subcylindric, 5–7 mm, 5(–8)-ribbed, faces strigose to scabrous or glabrous; pappi persistent, of 15–30, brownish, flattened, unequal, ciliate-barbellate, apically attenuate bristles in 1–2 series. x = 5 (4).
w, c United States.
Species 4 (4 in the flora).
Oönopsis is characterized by a relatively low habit, woody taproots with ample vegetative reproduction via one or two horizontal, spreading, sprouting branch roots, root crowns bearing woody, branched caudices, even-sized cauline leaves continuing up the stems and subtending the heads, foliaceous outer phyllaries, and yellow rays (in two species). All taxa are selenium-accumulating and indicators of selenium substrates. An undescribed fifth species has been noted (G. K. Brown 1993) from Pueblo and Fremont counties, Colorado; it is closely related to Oönopsis foliosa.
|1||Leaf blades linear to linear-oblanceolate, 0.7–5 mm wide; involucres 6-–11.5(–13) mm; phyllary apices abruptly acute to obtuse, apiculate to cuspidate; disc florets 7–28||> 2|
|1||Leaf blades oblanceolate to narrowly obovate or oblong-oblanceolate, 2–16 mm wide; involucres 10–25 mm; phyllary apices long-acuminate to long-acute, not apiculate or cuspidate; disc florets 10–45 or 53–150||> 3|
|2||Ray florets 5–11; cypselae 2.8–4 mm, tomentose||Oönopsis multicaulis|
|2||Ray florets 0; cypselae 5–6 mm, glabrous or sparsely scabrous||Oönopsis engelmannii|
|3||Stems glabrous; cauline leaves not auriculate or clasping; heads not immediately subtended by leaflike bracts, distalmost cauline abruptly reduced in size; ray florets 0; disc florets 10–45||Oönopsis wardii|
|3||Stems villosulous or glabrous; at least distal cauline leaves subauriculate and subclasping; heads immediately subtended by leaflike bracts similar to distal cauline leaves; ray florets 15–25 or 0; disc florets 53–150||Oönopsis foliosa|