Asclepias longifolia
Asclepias angustifolia
Florida milkweed, long-leaf milkweed
Arizona milkweed, narrow-leaf milkweed
1–few, spreading to decumbent, unbranched, 25–70 cm, puberulent with curved trichomes, not glaucous, rhizomes absent.
few–numerous, erect, sparsely to moderately branched, 20–60 cm, puberulent with curved trichomes in a line, not glaucous, rhizomes absent.
opposite or alternate, sessile or petiolate, with 1 or 2 stipular colleters on each side of petiole, also in axil;
petiole 0–2 mm, puberulent with curved trichomes;
blade linear to linear-lanceolate, 5–18 × 0.2–1 cm, chartaceous, base cuneate, margins entire, apex acute to attenuate, sometimes mucronate, venation brochidodromous, surfaces scabridulous to puberulent with curved trichomes, especially on veins, margins ciliate, laminar colleters absent.
persistent or gradually caducous from the base, opposite, petiolate, with 1 stipular colleter on each side of petiole on a ciliate interpetiolar ridge;
petiole 2–4 mm, surfaces puberulent with curved trichomes to glabrate;
blade linear, 3.5–10 × 0.2–0.8 cm, chartaceous, base cuneate, margins entire, apex acute, venation faintly brochidodromous to obscure, puberulent with curved trichomes on midvein, margins ciliate, laminar colleters absent.
terminal and extra-axillary at upper nodes, sessile or pedunculate, 13–28(–36)-flowered;
peduncle 0–6 cm, puberulent with curved trichomes, with 1 caducous bract at the base of each pedicel.
extra-axillary at upper nodes, pedunculate, 3–15-flowered;
peduncle 0.7–5 cm, puberulent with curved trichomes in a line, with 1 caducous bract at the base of each pedicel.
9–16 mm, puberulent with curved trichomes.
8–18 mm, puberulent with curved trichomes in a line.
erect to spreading;
calyx lobes narrowly lanceolate, 1.5–2 mm, apex acute, puberulent with curved trichomes;
corolla white to greenish cream, purple at lobe tips, lobes reflexed, oblong, 3–5 mm, apex obtuse, glabrous;
gynostegial column 0.2–0.5 mm;
fused anthers green or brown, cylindric, 1–1.5 mm, wings triangular to trapezoidal, widest at middle, slightly open at tip, apical appendages ovate;
corona segments pinkish lavender to red-violet, often with white apex, often a darker red-violet stripe or at base, sessile, laminar, strongly dorsally compressed, margins incurved, appressed to column, curved to subsaccate, 2–2.5 mm, exceeding point of anther wings, greatly exceeded by style apex, apex obtuse to truncate, glabrous, internal appendage absent or obscure, glabrous;
style apex shallowly depressed, greenish cream to green.
erect;
calyx lobes narrowly lanceolate, 2–3 mm, apex acute, puberulent with curved trichomes;
corolla cream, sometimes pink-striped or -tinged, to pink, lobes reflexed with spreading tips, elliptic, 4–5 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 0.8–1 mm;
fused anthers brown, columnar, 1.5–2 mm, wings narrowly right-triangular, closed, apical appendages deltoid;
corona segments cream, sometimes pink at base, stipitate, tubular, dorsally rounded, 3–3.5 mm, exceeding style apex, apex obtuse, glabrous, internal appendage acicular, exserted, arching over style apex, glabrous;
style apex shallowly depressed, cream.
ovate, 11–12 × 7–8 mm, margin winged, faces smooth;
coma 4–5 cm.
ovate, 4.5–6 × 3–4 mm, margin narrowly winged, faces smooth;
coma 2–3 cm.
erect on upcurved pedicels, narrowly fusiform, 8–13.5 × 0.7–1.2 cm, apex attenuate, smooth, puberulent with curved trichomes.
erect on straight pedicels, narrowly fusiform, 4–10 × 0.4–0.7 cm, apex long-acuminate to attenuate, smooth, glabrous.
Asclepias longifolia
Asclepias angustifolia
Asclepias longifolia has sometimes been treated to include A. hirtella as conspecific, as discussed under that species. As circumscribed here, the distribution of A. longifolia extends along the Atlantic Coastal Plain south of Delaware to Florida and westward to the Mississppi River. Reports of A. longifolia from west of the Mississippi River in Louisiana and in Texas are assigned here to A. hirtella. Hence, the range of A. longifolia in Louisiana is extremely limited, and the conservation status of this species warrants assessment in that state (Livingston, Saint Helena, Saint Tammany, Tangipahoa, and Washington parishes). Reports of A. longifolia from Maryland and West Virginia have not been confirmed, and the species is considered extirpated from Delaware. Otherwise, it is rare at the northern extent of its range and considered to be of conservation concern in North Carolina and Virginia (Greensville and Prince George counties).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
The common name Arizona milkweed is misleading, as Asclepias angustifolia is narrowly distributed and uncommon in Arizona but widely distributed and locally common across mountainous regions of Mexico. Like A. linaria, this widespread species is probably relictual in its canyon habitat in southern Arizona. Asclepias angustifolia has been documented from the Atascosa, Dragoon, Huachuca, Pajarito, Rincon, Santa Catalina, and Santa Rita mountains (Cochise, Pima, and Santa Cruz counties). As with many milkweeds, the floral displays of well-developed plants are magnets for large numbers of Lepidoptera and Hymenoptera. Like A. curassavica and other members of the Incarnatae clade (species 7–16), A. angustifolia develops rapidly from seed and transplants well, making it a desirable species for the garden. Although its frost hardiness is limited, it can be used as a horticultural annual.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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