1. Vernonia arkansana DC.
V. crinita Raf.
Pl. 300 g–j; Map
1261
Stems 70–160 cm
long, glabrous or nearly so, sometimes minutely hairy toward the tip, often
appearing somewhat glaucous. Leaf blades 8–20 cm long, linear to narrowly
elliptic-lanceolate, tapered at both ends, the margins sharply toothed or less
commonly entire or nearly so, usually appearing somewhat turned under, both
surfaces glabrous to sparsely hairy and appearing dotted with minute, impressed
resin glands (these sometimes difficult to observe in fresh material, but
darkening and becoming more noticeable in dried leaves). Heads with 50–120
florets. Involucre 9–16 mm long, hemispherical or somewhat bell-shaped, the
bracts 6–14 mm long, all but the outermost ones linear to narrowly lanceolate,
long-tapered and somewhat curled to a threadlike, sharply pointed tip,
cobwebby-hairy along the margins and sometimes also minutely hairy on the outer
surface, green, the midvein indistinct. Pappus brownish purple, the inner
bristles 6–7 mm long, the outer scales 0.7–1.0 mm long. Corollas 10–12 mm long.
Fruits 4–5 mm long. 2n=34. July–October.
Scattered in the
Ozark and Ozark Border Divisions, and uncommon in the Big Rivers (Kansas and
Oklahoma east to Missouri and Arkansas; introduced north- and eastward to
Wisconsin and New York). Banks of streams, margins of sloughs, fens, openings
of bottomland forests, mesic upland forests, bottomland prairies, and rarely
glades; also pastures and roadsides.
Vernonia
arkansana is a
characteristic species of stream banks and gravel bars in the Ozarks, but it
can occur in a variety of other habitats. Hybrids with other Missouri species
of Vernonia are relatively easily noted, because V. arkansana is
relatively distinctive in its larger heads and elongate involucral bracts. Cora
Steyermark (1939) grew seeds harvested from natural Ozarkian populations of V.
arkansana (as V. crinita) in a garden, and she concluded that
hybridization involving this species was relatively common, as the progeny
often exhibited variable and intermediate morphologies. Hybrids with V.
baldwinii are especially common (Jones et al., 1970) and often occur where
a road near a stream brings drier roadside and moister streamside habitats into
close proximity. Harms (1969) studied ironweeds in southeasternmost Kansas and
documented a population showing introgression between V. arkansana, V.
baldwinii, and V. missurica.