2. Boltonia decurrens (Torr. & A. Gray) A.W. Wood (decurrent false aster)
B. asteroides var. decurrens (Torr. & A.
Gray) Fernald & Griscom
B. latisquama var. decurrens (Torr. & A.
Gray) Fernald & Griscom
Pl. 231 c, d;
Map 964
Plants producing
basal offshoots but no rhizomes. Stems (50–)120–250 cm long.
Leaf blades 5–20 cm long, 5–25 mm wide, those of the lower and
median leaves oblanceolate to narrowly elliptic, those of the upper leaves
mostly narrowly elliptic to linear-elliptic, the base strongly decurrent below
the attachment point as a pair of wings of green tissue along the stem ridges
(the stems thus appearing irregularly winged). Inflorescences appearing leafy,
the bracts 0.5–5.0 cm long, 1–11 mm wide. Heads relatively
large, the receptacle usually 6–12 mm in diameter at flowering.
Involucre 3–5 mm long, the bracts in 3–5 subequal to somewhat
unequal series, narrowed or tapered to a sharply pointed tip or sometimes
rounded to an abrupt, short, sharp point. Ray florets 45–60, the
corolla 9–11(–14) mm long. Disc florets 250–400. Pappus
of disc florets a short, irregular crown of awns or narrow scales
0.1–0.4 mm long and 2(–4) awns 1–2 mm long, the longer
awns well developed in the disc florets, sometimes absent in the ray florets.
Fruits 1.5–2.5 mm long, the wings 0.3–0.5 mm wide. 2n=18.
August–October (rarely to December).
Uncommon in the
Big Rivers Division from Lincoln to St. Charles Counties with isolated
historical collections from the city of St. Louis and Cape Girardeau County; introduced in Howell and St. Louis Counties (endemic to the Illinois and adjacent
Mississippi River floodplains in Illinois and Missouri). Banks of rivers,
margins of ponds and lakes, and bottomland prairies; also margins of crop
fields, fallow fields, and levees.
The present
treatment follows that of Schwegman and Nyboer (1985) in recognizing this taxon
as a species rather than a variety within B. asteroides, as was done by
many earlier authors (Steyermark, 1963). Boltonia decurrens is heavily
dependent on periodic flooding or disturbance to eliminate competing vegetation
and to provide the high light and moist soil conditions that the achenes
require for germination (Smith and Keevin, 1998). During the Great Flood of 1993,
the entire global range of decurrent false aster was inundated for a period of
8–10 weeks, but in spite of gloomy predictions that the species would
be driven toward extinction, it responded relatively well to the flooding,
which created large areas of relatively open floodplain habitat. Overall,
however, populations have decreased in size and number in recent decades due to
the construction of levees and locks and dams along the Illinois and Mississippi Rivers, which have prevented flooding in many areas. In 1988, this globally
imperiled species was listed as Threatened by the U.S. Fish and Wildlife
Service under the Federal Endangered Species Act.