Asclepias tuberosa
Asclepias ovalifolia
asclépiade tubéreuse, butterfly milkweed
asclépiade à feuilles ovées, oval-leaf milkweed
1–numerous, erect to ascending, branched in inflorescence, 15–90 cm, densely hirsute, not glaucous, rhizomes absent.
1, erect, unbranched, 30–70 cm, densely puberulent with curved trichomes or pilosulous to tomentose, not glaucous, rhizomatous.
alternate, petiolate, with 1 or 2 stipular colleters on each side of petiole;
petiole 1–4 mm, densely hirsute;
blade elliptic, oblong, or oblanceolate to lanceolate or linear, 2–12 × 0.3–3 cm, chartaceous, base cuneate or obtuse to rounded, truncate, hastate, or cordate, margins entire, apex acute to attenuate or obtuse to rounded, venation brochidodromous to eucamptodromous, surfaces hirsute, more densely so on midvein abaxially, margins ciliate, 0–4 laminar colleters.
opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole;
petiole 3–10 mm, densely pilosulous to tomentose;
blade broadly ovate to oval or narrowly elliptic, 3–9 × 1.5–4.5 cm, chartaceous, base obtuse or rounded to truncate, margins entire, apex acute to obtuse, mucronate, venation brochidodromous, surfaces pilosulous abaxially, sparsely so adaxially except on veins, margins ciliate, 4–16 laminar colleters.
corymbs of extra-axillary umbels on branches, sessile or pedunculate, 5–27-flowered;
peduncle 0–4 cm, sometimes branched, hirsute, with 1 caducous bract at the base of each pedicel.
extra-axillary at upper nodes, sessile or pedunculate, 5–21-flowered;
peduncle 0–7 cm, densely pilosulous to tomentose, with 1 caducous bract at the base of each pedicel.
9–24 mm, puberulent with curved trichomes to pilosulous.
12–22 mm, densely pilosulous to tomentose.
erect;
calyx lobes narrowly lanceolate, 2–3 mm, apex acute, hirsute to puberulent with curved trichomes;
corolla reddish orange (nearly red) to orange or yellow, lobes reflexed with spreading tips, narrowly elliptic, (5–)6–8 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 1.2–1.5 mm, fused anthers yellow to yellowish green, cylindric, 2–3 mm, wings right-triangular, closed, apical appendages ovate;
corona segments reddish orange (nearly red) to orange or yellow, substipitate, conduplicate, dorsally flattened, sulcate, 5.5–7 mm, greatly exceeding style apex, apex acute, glabrous, internal appendage subulate, exserted, arching above style apex, glabrous;
style apex shallowly depressed, yellow to yellowish green.
erect to spreading;
calyx lobes lanceolate, 2–3 mm, apex acute, densely pilosulous;
corolla cream to yellowish, lobes reflexed with spreading tips, elliptic, 5–7 mm, apex acute, pilosulous abaxially at apex, glabrous adaxially;
gynostegial column 0.2–0.5 mm;
fused anthers green, cylindric, 1.5–2 mm, wings right-triangular, closed, apical appendages ovate;
corona segments cream to yellowish, subsessile, conduplicate, dorsally flattened, 3–4 mm, exceeding style apex, apex acute with proximal tooth on each side, glabrous, internal appendage falcate, exserted, sharply inflexed to ascending over style apex, glabrous;
style apex shallowly depressed, cream to pinkish.
ovate, 8–9 × 4–5 mm, margin winged, faces minutely rugulose;
coma 3–5 cm.
ovate, 5–6 × 3.5–4.5 mm, margin winged, faces rugulose;
coma 2.5–3 cm.
erect on upcurved pedicels, fusiform, 7–14 × 1.2–2 cm, apex long-acuminate or attenuate, smooth, hirsute.
erect on upcurved pedicels, lance-ovoid, 5–8 × 1.2–2 cm, apex acute to apiculate, smooth, densely pilosulous to tomentose.
= 22.
Asclepias tuberosa
Asclepias ovalifolia
Subspecies 3 (3 in the flora).
Asclepias tuberosa is one of the most familiar and beloved North American milkweeds and is a favored element of pollinator gardens because of the cheery orange flowers that attract abundant insect visitors. The clear latex is unusual in the genus and is often commented upon by collectors. The subspecies of A. tuberosa are highly intergrading. It is often difficult to satisfactorily place a given specimen in a particular subspecies; however, the great majority are readily assigned. It appears that the conspicuous variation in leaf morphology across the subspecies corresponds to genetically structured population variation (R. E. Woodson Jr. 1947). However, it is unknown to what extent cultivation and other human activities have blurred the distinctions among the geographic variants. Future recognition of the subspecies should be supported by genetic study with modern techniques. Although yellow-flowered plants predominate in the western plains, color variation is often pronounced in single populations, and yellow flowers may be encountered anywhere in the range. Hybridization with A. syriaca is documented, but is exceedingly rare. Presumed hybrids can be recognized by intermediate floral and vegetative traits.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Asclepias ovalifolia is the northernmost-ranging species in the genus, and over much of its range co-occurs with at most one other species of Asclepias. The quality of its habitat has been degraded by woody encroachment, presumably resulting from fire suppression. It appears to be secure in the core of its range in Minnesota, North Dakota, Manitoba, and Saskatchewan. Elsewhere there are conservation concerns, as in Illinois (Cook, Kankakee, Kendall, Lake, and McHenry counties), Michigan (Lake and Menominee counties), Montana (Carter and Sheridan counties), Wyoming (Crook County), and Ontario. Asclepias ovalifolia was collected in 1915 in British Columbia in a valley of the Columbia Mountains (Bain. s.n. [UBC]), far disjunct from the species’ range east of the Rocky Mountains. The occurrence has been considered to be adventive and not persistent (F. Lomer, pers. comm.). It has been reported from Nebraska based on the original determination of what became the type specimen of A. hallii; it is not known to have ever occurred in that state. Hybrids with A. syriaca are known, but appear to be rare, and can be recognized by possession of intermediate floral and vegetative traits.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Leaf bases hastate, blade margins crisped. | subsp. rolfsii |
1. Leaf bases cuneate, obtuse, rounded, truncate, or subcordate, blade margins planar. | → 2 |
2. Leaf bases cuneate to obtuse, rounded, or subcordate, apices rounded to acute, mostly east of the crest of the Appalachian Mountains. | subsp. tuberosa |
2. Leaf bases truncate or obtuse to cordate, apices acute to attenuate, mostly west of the crest of the Appalachian Mountains. | subsp. interior |
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