Perennials, 30–300 cm. Stems usually 1, erect (unbranched proximal to heads). Leaves basal and cauline; alternate; petiolate or sessile; blades palmately nerved, mostly cordate, deltate, elliptic, hastate, ovate, or reniform, sometimes lanceolate or lance-linear, margins entire, ± dentate to denticulate, sinuate, or lobed, faces usually glabrous. Heads discoid, in corymbiform arrays. Calyculi 0. Involucres cylindric to turbinate, 2.5–5 mm diam. Phyllaries persistent, 5 in 1–2 series, erect (spreading in fruit), distinct, ovate or oblong to linear (midveins sometimes winged), ± equal, margins scarious (hyaline). Receptacles flat or convex (usually with central cusp 0.5–2 mm), foveolate, epaleate. Ray florets 0. Disc florets 5, bisexual, fertile; corollas usually creamy or greenish white, rarely purplish distally, tubes longer than to equaling campanulate to funnelform throats, lobes 5, spreading or recurved, lanceolate; style branches: stigmatic areas continuous, apices truncate or truncate-penicillate (appendages essentially 0). Cypselae clavate, cylindric, ellipsoid, or ± fusiform, (4–)10–15-ribbed or -nerved, glabrous (resinous); pappi persistent, fragile, or readily falling, of 100–120+, white, smooth or barbellate bristles. x = 28.
e North America.
Species 8 (8 in the flora).
The name Cacalia Linnaeus has been misapplied to Arnoglossum.
|1||Phyllary midveins not winged (leaves ± membranous)||> 2|
|1||Phyllary midveins winged (leaves firm)||> 4|
|2||Basal leaves (and proximal cauline): blades ovate to narrowly lanceolate or lance-linear, margins usually entire||Arnoglossum ovatum|
|2||Basal leaves (and proximal cauline): blades ovate, ovate-cordate, or reniform, margins lobed or dentate||> 3|
|3||Stems smooth to weakly striate (stems and abaxial leaf faces glaucous)||Arnoglossum atriplicifolium|
|3||Stems ridged to angulate (stems and abaxial leaf faces not glaucous)||Arnoglossum reniforme|
|4||Basal leaves: blades ovate to cordate-ovate (bases truncate), margins denticulate; proximal cauline leaves deltate-hastate, margins dentate||Arnoglossum diversifolium|
|4||Basal leaves: blades elliptic, ovate, ovate-oblong, or lance-oblong, margins crenate, crenulate, denticulate, entire, serrulate-denticulate, or sinuate; proximal cauline leaves ovate or elliptic, margins crenulate, denticulate, entire, serrate, or sinuate||> 5|
|5||Phyllary wings (erose) highest at bases (lateral veins of basal leaves appressed to midveins 2–4 cm, then spreading)||Arnoglossum album|
|5||Phyllary wings (entire or sinuate) ± uniform or highest at apices (lateral veins of leaves spreading from bases)||> 6|
|6||Involucres 12–15 mm; corollas (9–)11–12 mm; cauline leaves: margins crenulate||Arnoglossum floridanum|
|6||Involucres 8–14 mm; corollas 7–11.5 mm; cauline leaves: margins crenulate, denticulate, entire, serrulate, or sinuate||> 7|
|7||Involucres (9.5–)10–12(–14) mm; corollas 8–10(–11.5) mm (mid-stem leaves petiolate, bases rounded)||Arnoglossum plantagineum|
|7||Involucres (8–)9.5–10(–12) mm; corollas 7–8(–9.5) mm (mid-stem leaves sessile, bases broadly cuneate)||Arnoglossum sulcatum|