13. Boltonia
L’Hér. (false aster) (Morgan, 1967)
Contributed by
Sarah M. Tofari
Plants robust
perennial herbs, fibrous-rooted, with rhizomes or basal offshoots, sometimes
somewhat woody at the base. Stems solitary or few, 40–250 cm long,
erect or ascending, with usually numerous ascending to loosely ascending
branches above the basal 1/3, with prominent pale ridges, glabrous. Basal
leaves absent at flowering, narrowly oblanceolate to oblong-obovate. Stem
leaves mostly sessile, progressively reduced toward the stem tip, the blades
oblanceolate to elliptic or linear, bluntly to sharply pointed at the tip,
tapered to long-tapered at the base, the margins entire or minutely toothed,
the surfaces glabrous. Inflorescences panicles, these often large and highly
branched, flat-topped or more commonly rounded, the heads solitary at the
branch tips, the branches with numerous linear to linear-lanceolate or linear-elliptic,
leaflike bracts. Heads radiate, not sticky or resinous. Involucral bracts in
2–5(6) unequal to subequal, overlapping series, linear to lanceolate,
oblanceolate, or spatulate, the tip ascending, differentiated into a somewhat
thickened, green to yellowish green central band, and narrow to relatively
broad, pale margins, these occasionally minutely toothed, glabrous. Receptacle
hemispherical or conical, sometimes with inconspicuous, minute, irregular
ridges around the concave attachment points of the florets. Ray florets
20–60, pistillate, the corolla white or less commonly pinkish- to
purplish-tinged. Disc florets numerous (50–400 or more), perfect, the
corolla yellow, not persistent at fruiting. Pappus a short, irregular crown of
4–10(–12) minute awns or narrow scales and 2(–4) longer
(0.5–2.0 mm) awns, the longer awns often absent in the ray florets and
sometimes also in the disc florets. Fruits of 2 types; 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. Five species, U.S., Canada.
Boltonia species superficially resemble Erigeron,
but recent molecular and morphological studies (Noyes and Rieseberg, 1999;
Nesom and Noyes, 2000) have suggested that Boltonia and two other small groups
formerly associated with Erigeron are more closely related to Symphyotrichum
and some other North American genera within the tribe Astereae. The two close
relatives of Boltonia are the genera Chloracantha G.L. Nesom et
al., which ranges from Central America to the southwestern United States, and Batopilasia G.L. Nesom & Noyes, which is found only in a small area of
southwestern Chihuahua, Mexico.