Asclepias tuberosa
Asclepias latifolia
asclépiade tubéreuse, butterfly milkweed
broad-leaf milkweed, corn-kernel milkweed
1–numerous, erect to ascending, branched in inflorescence, 15–90 cm, densely hirsute, not glaucous, rhizomes absent.
1–10, erect, unbranched, 25–100 cm, puberulent with curved trichomes or thinly tomentose to glabrate, sometimes 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, sessile or petiolate, with 1–4 stipular colleters on each side of petiole, sometimes also in axil;
petiole 0–4 mm, thinly tomentose to glabrate;
blade oval or oblong to ovate or orbiculate, 5.5–14 × 3–14 cm, subsucculent to coriaceous, base cordate, sometimes clasping, margins entire, apex truncate to rounded, sometimes emarginate, mucronate, venation brochidodromous, surfaces thinly tomentose to glabrate, sometimes glaucous, margins minutely ciliate to glabrous, 24–80 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, sessile or pedunculate, 20–59-flowered;
peduncle 0–2.5 cm, puberulent with curved trichomes to pilosulous, with 1 caducous bract at the base of each pedicel.
9–24 mm, puberulent with curved trichomes to pilosulous.
15–35 mm, densely tomentose to glabrate.
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 pendent;
calyx lobes lanceolate, 4–5 mm, apex acute, tomentose to glabrate;
corolla green, lobes reflexed, elliptic to oval, 7–9 mm, apex acute, glabrous abaxially, papillose at base adaxially;
gynostegial column 1–1.5 mm;
fused anthers green, cylindric, 3–3.5 mm, wings right-triangular, closed, apical appendages ovate;
corona segments cream, sometimes dorsally yellow, aging yellow, stipitate, conduplicate, dorsally rounded, 3–5.5 mm, equaling to slightly exceeding style apex, apex truncate, oblique, papillose, internal appendage falcate, exserted, sharply inflexed over style apex, papillose;
style apex shallowly depressed, green.
ovate, 8–9 × 4–5 mm, margin winged, faces minutely rugulose;
coma 3–5 cm.
ovate, 7–8 × 5–6 mm, winged, faces minutely rugulose to smooth;
coma 3–4 cm.
erect on upcurved pedicels, fusiform, 7–14 × 1.2–2 cm, apex long-acuminate or attenuate, smooth, hirsute.
erect on upcurved pedicels, ovoid, 6.5–9.5 × 2–3 cm, apex obtuse to apiculate, smooth, minutely pilosulous to thinly tomentulose.
= 22.
= 22.
Asclepias tuberosa
Asclepias latifolia
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 latifolia is a distinctive species of the western Great Plains and Colorado Plateau, rising above short grasses and appearing as squat, leafy pagodas. It is most likely to be confused with A. arenaria (which is restricted to sandy substrates) due to the overlapping leaf shapes and floral colors of these species. Asclepias latifolia favors clayey, often rocky soils, but can be found also on sandy soils, especially on the Colorado Plateau, outside the range of A. arenaria. These species can be distinguished by habit (erect in A. latifolia versus erect to decumbent in A. arenaria), vestiture (more uniformly and persistently hairy in A. arenaria), petioles (absent or nearly so in A. latifolia versus present in A. arenaria), and the flower and seed characters included in the key. Asclepias speciosa in the absence of reproductive structures is also commonly confused with A. latifolia, but the leaves of A. speciosa are distinctly petiolate, persistently hairy, and typically taper to the apex. There is an apparent gap in the distribution of A. latifolia on the eastern Colorado Plateau, in northwestern New Mexico and southwestern Colorado, but the disjunct portions of the range are not accompanied by phenotypic divergence. Asclepias latifolia is limited in Nebraska to southwestern counties (Deuel, Dundy, Franklin, and Hayes), but it is apparently not uncommon there. Likewise, it is common in its limited range in Utah (Garfield, Grand, Kane, San Juan, and Wayne counties).
(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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