Boltonia decurrens (Torr. & A. Gray) Alph. Wood

Decurrent False Aster


CC = 8
CW = -5
MOC = 7
SRank = S1

© SRTurner

Family - Asteraceae/Astereae

Habit - Fibrous-rooted perennial forb, producing basal offshoots but no rhizomes.

Boltonia_decurrens_rosette.jpg Basal offset.

© SRTurner

Stems - Ascending to erect, to 2.5 m, usually much branched in the apical half, glabrous, prominently winged with decurrent tissue from leaf bases.

Boltonia_decurrens_stem1.jpg Stem and nodes with conspicuous decurrent tissue.

© SRTurner

Boltonia_decurrens_stem2.jpg Stem and nodes.

© SRTurner

Leaves - Alternate, simple, sessile. 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 surfaces glabrous, the bases strongly decurrent below the attachment point as a pair of wings of green tissue along the stem ridges, the stems thus appearing irregularly winged.

Boltonia_decurrens_leaf1.jpg Leaf adaxial.

© SRTurner

Boltonia_decurrens_leaf2.jpg Leaf abaxial, showing continuation of leaf tissue along stem at right.

© SRTurner

Inflorescences - Leafy, open panicles of numerous heads, the heads solitary at branch tips, the branches with numerous leafy bracts, these linear-lanceolate, 0.5-5.0 cm long, 1-11 mm wide.

Boltonia_decurrens_inflorescence.jpg Inflorescence (partial).

© SRTurner

Boltonia_decurrens_inflorescence2.jpg Inflorescence (partial).

© SRTurner

Heads - Radiate. 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.

Boltonia_decurrens_heads.jpg Flowering heads.

© SRTurner

Boltonia_decurrens_head.jpg Flowering head.

© SRTurner

Boltonia_decurrens_involucre.jpg Involucre.

© SRTurner

Flowers - Ray florets 45-60, pistillate, the corolla 9-11 mm long, white. Disc florets 250-400, perfect, the corollas yellow. Pappus of disc florets a short, irregular crown of awns or narrow scales 0.1-0.4 mm long and 2 awns 1-2 mm long, the longer awns well developed in the disc florets, sometimes absent in the ray florets.

Boltonia_decurrens_florets1.jpg Disks and rays.

© SRTurner

Boltonia_decurrens_florets2.jpg Florets.

© SRTurner

Fruits - Achenes 1.5-2.5 mm long, those developing from the disc florets wedge-shaped to obovate in outline, relatively strongly flattened, broadly rounded or angled to shallowly notched at the tip, the margins winged, the surface and margins often minutely hairy, tan to grayish brown with lighter wings; fruits developing from ray florets more or less wedge-shaped, 3-angled, with 3 narrow wings.

Flowering - August - October.

Habitat - Riverbanks, pond margins, bottomland prairies, margins of fields, levees.

Origin - Native to the U.S.

Lookalikes - B. asteroides, Erigeron spp.

Other info. - This species is uncommon in Missouri, and is in fact listed as endangered by both Missouri and the federal government. Its global distribution is mostly restricted to floodplain of the Illinois River and the region of the Illinois' confluence with the Mississippi River. It is an easily recognized species, defined by its large panicles of white flowering heads with yellow centers, and, especially, the distinctive flanges of green tissue which run from the leaf bases down the stem. The latter feature is what distinguishes it from the much more common B. asteroides, and also what contributes the plant's specific epithet.

The ecology and life cycle of the species has been studied extensively by the late Marian Smith at SIUE. It is subject to pronounced "boom-bust" cycles, with huge populations of plants exploding as an early successional stage following certain flooding events. Over a few years these populations dwindle until virtually no plants remain. Human efforts to control flooding along the great rivers have drastically reduced these events crucial to the plant's long-term survival.

Photographs taken near Gilbert Lake, Jersey County, IL, 9-30-2007, and at B. K. Leach Memorial Conservation Area, Lincoln County, MO, 9-13-2021 (SRTurner).