Asclepias cordifolia
Asclepias oenotheroides
heart-leaf milkweed, purple milkweed
hierba de zizotes, zizotes milkweed
1–20, ascending to spreading, unbranched, 25–100 cm, glabrous, glaucous, rhizomes absent.
1–7, erect to spreading or decumbent, unbranched or rarely branched near base, 10–50 cm, puberulent with curved trichomes to hirsutulous, not glaucous, rhizomatous.
opposite, sessile, stipular colleters absent;
blade ovate to lanceolate, 3.5–11 × 1.8–8 cm, chartaceous, base cordate, clasping, margins entire, apex acute, mucronate, venation brochidodromous to eucamptodromous, surfaces glabrous, glaucous, margins minutely ciliate, laminar colleters absent.
persistent or gradually caducous from base, opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole;
petiole 2–20 mm, puberulent with curved trichomes to hirtellous;
blade ovate or lanceolate to oblong or elliptic, sometimes conduplicate, 4–11 × 1.2–6.5 cm, chartaceous, base cuneate to obtuse, margins sometimes crisped, apex obtuse to rounded, venation eucamptodromous to faintly brochidodromous, surfaces hirtellous, laminar colleters absent.
terminal, branched, sometimes also extra-axillary at upper nodes, pedunculate, 5–20-flowered;
peduncle 0.3–6.5 cm, apically sparsely pilose to glabrate, with few bracts.
extra-axillary, sessile or pedunculate, 8–32-flowered;
peduncle 0–1 cm, hirtellous, with 1 caducous bract at the base of each pedicel.
16–37 mm, sparsely pilose.
10–20 mm, hirtellous.
erect to pendent;
calyx lobes elliptic to lanceolate, 3–5 mm, apex acute, pilose;
corolla red-violet, lobes reflexed with spreading tips, oval, 6–7 mm, apex acute, glabrous;
gynostegial column 1–1.5 mm;
fused anthers brown, cylindric, 1.5–2 mm, wings right-triangular, open at tip, apical appendages deltoid;
corona segments white, tinged pink to red-violet at base, sessile, tubular, 2–3 mm, exceeded by style apex, base saccate, apex truncate, oblique, glabrous, internal appendage absent;
style apex shallowly depressed, pink to red-violet.
erect to ascending;
calyx lobes lanceolate, 3.5–4 mm, apex acute, hirtellous;
corolla green, sometime tinged red or brown, sometimes faintly striate, lobes reflexed, elliptic to linear-lanceolate, (7–)9–12 mm, apex acute, glabrous at tips abaxially or hirtellous throughout, glabrous adaxially;
gynostegial column 1–1.5 mm;
fused anthers brown, sometimes green proximally, obconic, 2–2.5 mm, wings triangular, widest at middle, closed, apical appendages ovate;
corona segments green, sometimes tinged bronze, apex white or cream, fading yellow, sessile, sinuous-tubular, relatively slender, (5–)7–10 mm, greatly exceeding style apex, apex slightly flared, deeply emarginate, lobed on each side, minutely papillose to glabrate, internal appendage lingulate, sharply incurved, barely exserted, exceeded by segment margin, minutely papillose to glabrate.
ovate, 8–9 × 5–7 mm, margin not winged, faces reticulate-rugulose;
coma 3–3.5 cm.
ovate to oval, 6–8 × 5–6 mm, margin winged, faces smooth;
coma 2–3 cm.
erect on upcurved pedicels, lance-ovoid, 7.5–10.5 × 1.5–1.8 cm, apex long-acuminate, smooth, glabrous, glaucous.
erect on upcurved pedicels, lance-ovoid, 4.5–9.5 × 1.2–2.5 cm, apex attenuate to acuminate, smooth, sometimes faintly striate, puberulent with curved trichomes to hirtellous.
= 22.
Asclepias cordifolia
Asclepias oenotheroides
Fresh leaves and stems of Asclepias cordifolia are often slightly or strongly colored bluish, grayish, or purplish. This is one of the few American species of Asclepias with cavitate corona segments that lack adaxial appendages. Such species were segregated along with diverse African species in Gomphocarpus R. Brown, a polyphyletic segregate (M. Fishbein et al. 2011; D. Chuba et al. 2017). Asclepias cordifolia is a distinctive species unlike any other within its range. It is phylogenetically and geographically isolated, although not highly derived morphologically. In Nevada, A. cordifolia is restricted to the Sierra Nevada, in Carson City, Douglas, and Washoe counties. Its range extends to northern California and southwestern Oregon.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Asclepias oenotheroides is one of the most widespread American milkweeds, ranging from southeastern Colorado to Nicaragua. It is very common in southern and western Texas and throughout valleys and plains across Mexico. However, it is rare at the northern limit of its range in Colorado (known only from Las Animas County), where it is considered to be of conservation concern, Louisiana (known only from Jefferson Davis Parish), and Oklahoma. In the absence of flowers, it can be difficult to distinguish from its close relatives: A. nyctaginifolia, in southeastern Arizona and southwestern New Mexico, and A. emoryi in southern Texas. Compared to A. oenotheroides, the leaves of A. nyctaginifolia tend to be broader and more consistently ovate, whereas the leaves of A. emoryi tend to be narrower and more consistently elliptic or linear-lanceolate. However, A. oenotheroides is highly variable, and the overlap with these relatives is substantial. Even in flower, pressed specimens can be challenging to distinguish. The corona segments of A. nyctaginifolia are thicker and wider than those of A. oenotheroides, which is easily observed on fresh flowers but may be obscured by drying. Similarly, in fresh flowers the flared segment apex that exceeds the exserted appendage in A. oenotheroides is easily distinguished from the segment apex that is closed by the flush appendage in A. emoryi, yet this obvious distinction is frustratingly obscure in dried material. For most of the range of A. oenotheroides the length of the corona segments greatly exceeds that of A. emoryi. However, along the southern Texas coastal plain, and especially on the barrier islands, the length of corona segments of A. oenotheroides is shorter, overlapping slightly with A. emoryi. Such plants correspond to the type of Podostemma helleri. In addition, hybridization of A. oenotheroides with both A. emoryi and A. nyctaginifolia is suspected, based on a few, scattered specimens with intermediate floral morphology in the regions of overlap with each species.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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