Asclepias linaria
Asclepias oenotheroides
hierba del cuervo, needle leaf milkweed, pineneedle milkweed
hierba de zizotes, zizotes milkweed
few–numerous, erect, branched, especially distally, 30–70 cm, woody, bark brown to gray, twigs puberulent with curved trichomes, not 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.
eventually caducous, alternate, spiral to irregular, sessile, with 1 stipular colleter on each side of leaf base;
blade linear, needlelike, 1.5–4 × 0.1–0.15 cm, chartaceous, base cuneate, margins revolute, apex acute, mucronate, venation obscure, sparsely pilosulous to glabrate, 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.
extra-axillary, sessile or pedunculate, 9–30-flowered;
peduncle 0–2.5 cm, puberulent with curved trichomes to pilosulous, with 1 caducous bract at the base of each pedicel.
extra-axillary, sessile or pedunculate, 8–32-flowered;
peduncle 0–1 cm, hirtellous, with 1 caducous bract at the base of each pedicel.
10–14 mm, pilosulous.
10–20 mm, hirtellous.
erect to pendent;
calyx lobes lanceolate to ovate, 2–3 mm, apex acute, sparsely pilosulous to glabrate;
corolla green to cream, often tinged red or purple, lobes reflexed with spreading tips, elliptic, 3.5–5 mm, apex acute, glabrous abaxially, minutely hirtellous at base adaxially, 1 margin ciliate;
gynostegial column 0.2–0.5 mm;
fused anthers brown, obconic, 1–1.5 mm, wings right-triangular, closed, apical appendages ovate, erose;
corona segments cream, sometimes with greenish or purplish dorsal stripe, subsessile or sessile, cupulate, 2.5–3 mm, exceeding style apex, apex obtuse to rounded, glabrous, internal appendage rod-shaped, slightly exserted, glabrous;
style apex shallowly depressed, green.
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.
naviculate, ovate, 5–6 × 3–4 mm, margin very narrowly winged, faces rugulose, the concave one conspicuously so;
coma 1.5–2 cm.
ovate to oval, 6–8 × 5–6 mm, margin winged, faces smooth;
coma 2–3 cm.
erect on upcurved pedicels, ovoid, 3.5–5 × 0.6–1 cm, apex acuminate, smooth, glabrous.
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 linaria
Asclepias oenotheroides
Asclepias linaria is arguably the most distinctive milkweed species in the Americas. It is the only species with woody stems and the only one to form hemispherical shrubs with needlelike leaves. Small plants with few stems are easily mistaken for seedling conifers. This species is widespread and occupies a great variety of habitats in Mexico. It enters the flora area in southeastern Arizona and in southwestern New Mexico only in the Peloncillo Mountains (Hidalgo County); its occurrence in the flora area is evidently relictual. In the region, it is restricted to lower reaches of protected canyons that ameliorate aridity and freezing temperatures, sites that harbor other tropical and subtropical species reaching their northern limits. The plants are often quite floriferous and attract an abundance of Hymenoptera, Lepidoptera, and Diptera.
(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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