Asclepias sullivantii
Asclepias macrosperma
asclépiade de Sullivant, prairie milkweed, Sullivant's milkweed
dwarf milkweed, large-seed milkweed, large-seed or dwarf or Eastwood's milkweed
solitary, erect, unbranched, 55–90 cm, glabrous, glaucous, rhizomatous.
1–12, decumbent, unbranched or branched near base, 6–15 cm, densely puberulent with curved trichomes, not glaucous, rhizomatous.
opposite, sessile, with 1 or 2 stipular colleters on each side of leaf base;
blade lanceolate or ovate to oblong, 6.5–15 × 1.5–9 cm, succulent, base cordate, margins entire, apex obtuse to rounded or acute, sometimes emarginate, mucronate, venation brochidodromous, surfaces glabrous, glaucous, margins eciliate, 4–12 laminar colleters.
opposite or subopposite to alternate, petiolate, with 1 stipular colleter on either side of petiole;
petiole 1–5 mm, densely puberulent with curved trichomes;
blade lanceolate to linear-lanceolate or lance-ovate, 2.5–7 × 0.5–2 cm, chartaceous, base cuneate to truncate, margins crisped, apex attenuate, mucronate, venation obscure to faintly eucamptodromous, surfaces sparsely pilosulous to glabrate, midvein puberulent with curved trichomes to pilosulous, margins densely ciliate, laminar colleters absent.
extra-axillary at upper nodes, sometimes appearing terminal, pedunculate, 9–29-flowered;
peduncle 1–6 cm, glabrous, glaucous, with 1 caducous bract at the base of each pedicel.
terminal, sessile, 12–40-flowered, bracts few.
22–36 mm, glabrous, glaucous.
9–19 mm, densely pilose.
erect;
calyx lobes lanceolate, 4–5 mm, apex acute, glabrous, glaucous;
corolla dark pink, pale at base of lobes, lobes reflexed, sometimes with spreading tips, elliptic, 8–12 mm, apex acute, glabrous;
gynostegial column 1–1.5 mm;
fused anthers truncately green, obconic, 2.5–3.5 mm, wings narrowly right-triangular, open at base, apical appendages ovate;
corona segments pale to dark pink, subsessile, tubular, flattened dorsally, 5–7 mm, exceeding style apex, apex broadly obtuse, oblique, glabrous, internal appendage subulate, exserted, sharply inflexed over style apex, glabrous;
style apex shallowly depressed, green.
erect to pendent;
calyx lobes elliptic, 2.5–3 mm, apex acute, pilose;
corolla green, tinged red (especially abaxially), lobes reflexed, oval, 4–5.5 mm, apex acute, glabrous;
gynostegial column 0.2–0.8 mm;
fused anthers brown, cylindric, 1–1.5 mm, wings right-triangular, slightly open at tip, apical appendages ovate;
corona segments yellow to ochroleucous, subsessile, tubular, 2–3 mm, equaling or slightly exceeding style apex, apex truncate, glabrous, internal appendage falcate, exserted, sharply inflexed towards or over style apex, glabrous;
style apex shallowly depressed, green or pink.
ovate, 7–9 × 5–6 mm, margin winged, faces minutely rugulose;
coma 3.5–4.5 cm.
ovate, 8–12 × 6–8 mm, margin thickly winged, faces densely rugulose;
coma 1.5–2 cm.
erect on upcurved pedicels, lance-ovoid, 7–11 × 1.5–3 cm, apex acuminate, sparsely muricate, sparsely pilosulous to glabrate, glaucous.
erect on upcurved pedicels, ovoid, 5–6.5 × 1.2–2 cm, apex acuminate, rugose, faintly striate, densely pilosulous.
= 22.
Asclepias sullivantii
Asclepias macrosperma
The distribution of Asclepias sullivantii is coextensive with the tallgrass prairie, where it favors moist sites. The broad, smooth, glaucous, clasping leaves, often with pink venation, are similar only to A. amplexicaulis in the region, but the latter species favors dry sites and has a long, terminal peduncle. Because of the tremendous reduction in the extent and quality of tallgrass prairie, A. sullivantii is presumed to be less common than in former times and is considered to be rare and of conservation concern in Michigan, Minnesota, Wisconsin, and Ontario (Chatham-Kent, Elgin, Essex, Lambton, and Middlesex counties). It may be extirpated from North Dakota (historically in Cass and Richland counties) and South Dakota (historically in Clay, Lincoln, and Union counties). In Nebraska, it is limited to the eastern one-third of the state. Nonetheless, it is encountered commonly in suitable habitat along roadsides in the core of its range, in Illinois and Kansas. Asclepias sullivantii commonly co-occurs with and is often mistaken for A. syriaca from a distance but is easily distinguished by its smaller stature, ascending leaves, and the concentration of umbels at the apex of the stem, in addition to the glabrous and glaucous herbage that can be observed with closer examination. It is known to hybridize rarely with A. syriaca, and presumed hybrids can be recognized by intermediate vegetative and floral features.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Asclepias macrosperma has not been consistently recognized as distinct from A. involucrata, as discussed under that species. It is quite homogeneous across its range on the Colorado Plateau, and intermediates with A. involucrata only occur where the ranges contact on the southern and eastern margins of the Plateau. It is readily distinguished from typical A. involucrata by broader leaves with crisped margins and smaller corona segments that are less compressed, less flared apically, and nearly uniformly yellow, as opposed to cream with a dark dorsal stripe. Also, A. macrosperma is largely confined to sandy, often unstabilized substrates, whereas A. involucrata occurs on stable, rocky, clay to sandy soils across most of its range. Asclepias macrosperma has been documented at few sites in Colorado (Montezuma County) and New Mexico (San Juan County) and should be considered to be of conservation concern in these states. It appears secure in Utah and on Navajo lands in Arizona.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
IL Wildflowers
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