1. Conoclinium coelestinum (L.) DC. (mist-flower, blue boneset, wild ageratum)
Eupatorium
coelestinum L.
Pl. 267 a–c; Map
1108
Plants
perennial, with rhizomes. Stems 1 or few, unbranched or few- to
several-branched below the inflorescence, 25–90 cm long, erect or ascending,
moderately to densely pubescent with short, curly hairs. Leaves opposite (the
nodes well separated), short- to long-petiolate. Leaf blades 1–10 cm long,
triangular-ovate to narrowly triangular, broadly angled to truncate at the
base, narrowed or tapered to a usually sharply pointed tip, the margins
shallowly scalloped or bluntly toothed, both surfaces glabrous or minutely
hairy, usually only along the veins, the undersurface also glandular, with
mostly 3 main veins. Inflorescences small panicles or stalked clusters at the
branch tips, flat-topped or less commonly dome-shaped. Heads with 35–70 disc
florets. Involucre 3–5 mm long, the bracts 18–30 (the head often also subtended
by 1 or a few other narrower bracts), in usually 2 or 3 somewhat unequal to
nearly equal, overlapping series, narrowly elliptic to narrowly lanceolate,
tapered to a sharply pointed, often purple tip, all but the outermost
noticeably but finely few-nerved or few-ribbed, sparsely to moderately
short-hairy and usually also glandular. Receptacle conical. Corollas purple or
lavender-blue (rarely white). Pappus of numerous capillary bristles (although
sometimes appearing relatively sparse). Fruits 1.6–2.4 mm long, finely
5-ribbed, slightly wedge-shaped in profile (usually slightly and unevenly tapered
at the base), glabrous, the ribs smooth or with a few minute, ascending teeth,
lighter colored, the body otherwise irregularly glandular and dark brown to
black. 2n=20. August–October.
Scattered,
mostly south of the Missouri River (eastern U.S. west to Nebraska and Texas;
Canada). Bottomland forests, swamps, banks of streams and rivers, margins of
ponds and lakes, marshes, and fens; also ditches, gardens, railroads,
roadsides, and shaded to open, disturbed areas.
Several
independent molecular studies have suggested that Conoclinium forms a
natural group with Ageratum and Fleischmannia that is only
distantly related to Eupatorium in the strict sense within the tribe
Eupatorieae (Schilling et al., 1999; Schmidt and Schilling, 2000; Ito et al.,
2000b). See the treatment of Fleischmannia for further discussion. A
rare, white-flowered mutant has been called E. coelestinum f. album
Alexander.