Asclepias fascicularis
Asclepias oenotheroides
Mexican whorled milkweed, narrow-leaf milkweed, narrow-leaf or Mexican or Mexican whorled milkweed
hierba de zizotes, zizotes milkweed
few–numerous, erect, sparsely to moderately branched, 50–150 cm, glabrous, 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.
3–5-whorled, sessile or petiolate, with 1–3 stipular colleters on each side of petiole on a ciliate interpetiolar ridge;
petiole 0–4 mm, margins puberulent with curved trichomes;
blade linear to linear-lanceolate or narrowly elliptic, often somewhat conduplicate, 4.5–13 × 0.2–1.8 cm, membranous, base cuneate, margins entire, apex acute or attenuate to obtuse, mucronate, venation obscure to faintly eucamptodromous, surfaces glabrous, margins eciliate, 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 and extra-axillary at upper nodes, sometimes branched, pedunculate, 10–37-flowered;
peduncle 0.4–5.5 cm, puberulent with curved trichomes in a line to glabrate, 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.
9–14 mm, puberulent with curved trichomes to pilosulous.
10–20 mm, hirtellous.
erect;
calyx lobes lanceolate, 1.5–2 mm, apex acute, puberulent with curved trichomes to pilosulous;
corolla pale to dark pink, rarely pale green with a pink tinge, lobes reflexed with spreading tips, oval, 3–5 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 1–1.5 mm;
fused anthers green, cylindric, 1.5–2 mm, wings narrowly right-triangular, closed, apical appendages deltoid;
corona segments cream, often tinged or striped pink, stipitate, cupulate, dorsally somewhat flattened, 1.5–2 mm, exceeded by style apex, apex obtuse, glabrous, internal appendage acicular, exserted, arching towards style apex, glabrous;
style apex shallowly depressed, cream.
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, 6–7 × 4–5 mm, margin winged, faces minutely rugulose;
coma 2.5–3 cm.
ovate to oval, 6–8 × 5–6 mm, margin winged, faces smooth;
coma 2–3 cm.
erect on straight pedicels, fusiform, 6–9 × 0.5–1 cm, apex attenuate, 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 fascicularis
Asclepias oenotheroides
Asclepias mexicana Decaisne was misapplied to A. fascicularis in the past; this is the legitimate name of a related species endemic to southern and eastern Mexico. The common name Mexican (whorled) milkweed stems from this past confusion. Compared to its close relatives A. angustifolia, A. linearis, A. pumila, A. subverticillata, and A. verticillata, the leaves of A. fascicularis are not particularly narrow (despite the implication of another common name). However, very narrow leaves are found in A. fascicularis when it is growing at relatively dry sites, especially at the eastern limit of its range in southeastern Idaho. Such specimens (for example, Mumford 272 [MO], Atwood 28495 [NY]) have been attributed in the past to A. subverticillata in error. Asclepias fascicularis is completely allopatric with its Incarnatae clade relatives (species 7–16). Like these species, it is easily cultivated, and its seeds are widely available. In Washington, the range of A. fascicularis is restricted largely to the valleys of the Columbia and Spokane rivers and in Idaho to the Snake and Weiser rivers.
(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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