Asclepias longifolia
Asclepias hallii
Florida milkweed, long-leaf milkweed
Hall's milkweed
1–few, spreading to decumbent, unbranched, 25–70 cm, puberulent with curved trichomes, not glaucous, rhizomes absent.
1–50, erect to ascending, unbranched or occasionally branched in inflorescence, 30–70 cm, puberulent with curved trichomes or pilose to glabrate, not glaucous, rhizomatous.
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.
alternate to subopposite (sometimes congested into pseudo-whorls), petiolate, with 1–4 stipular colleters on each side of petiole;
petiole 10–20 mm, puberulent with curved trichomes to pilosulous;
blade narrowly lanceolate to ovate, 5–16 × 1.5–9 cm, chartaceous, base obtuse to truncate, often oblique or unequal, margins entire, apex acute to obtuse, mucronate, venation brochidodromous, surfaces pilosulous or tomentulose to glabrate, more densely so on veins, margins ciliate, 10–20 comparatively large laminar colleters.
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, sometimes branched, pedunculate, 9–29-flowered;
peduncle 0.5–10.5 cm, pilose to tomentulose, with 1 caducous bract at the base of each pedicel.
9–16 mm, puberulent with curved trichomes.
16–28 mm, densely pilose to tomentulose.
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 to spreading;
calyx lobes lanceolate, 3–4 mm, apex acute, pilose;
corolla pale pink to red or green with pink or red tinge, lobes reflexed with spreading tips, lance-ovate, 7–8 mm, apex acute to obtuse, glabrous abaxially, minutely papillate at base adaxially;
gynostegial column 0.5–1 mm;
fused anthers brown, obconic, 2–2.5 mm, wings curved and widest at base to nearly right-triangular, closed, base distended, apical appendages ovate, erose;
corona segments cream with red or pink to purple dorsal stripe, sessile, conduplicate, dorsally flattened, 5–6.5 mm, greatly exceeding style apex, apex acute, glabrous, internal appendage falcate, exserted, sharply inflexed over style apex, glabrous;
style apex shallowly depressed, cream to pink.
ovate, 11–12 × 7–8 mm, margin winged, faces smooth;
coma 4–5 cm.
narrowly ovate, 6–7 × 4 mm, margin winged, faces and wings rugulose;
coma 2.5–3.5 cm.
erect on upcurved pedicels, narrowly fusiform, 8–13.5 × 0.7–1.2 cm, apex attenuate, smooth, puberulent with curved trichomes.
erect on upcurved pedicels, lance-ovoid, 8–12 × 0.7–1.5 cm, apex acuminate, smooth, pilosulous.
Asclepias longifolia
Asclepias hallii
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.)
Asclepias hallii is the only milkweed likely to be found above 2500 m in the Rocky Mountain and Intermountain regions, where it is found mostly on rocky canyon slopes. It appears to be a shorter-statured derivative of A. speciosa, which it greatly resembles, and which is the only species with which it commonly co-occurs. The range of A. hallii extends into the plains along river valleys and there overlaps with A. speciosa. Hybrids between these species have been documented only rarely in Colorado, and one of the syntypes of A. curvipes from Wyoming may represent this hybrid. Compared to A. speciosa, A. hallii is shorter statured, the leaves are narrower and are regularly subopposite or alternate rather than strictly opposite, and the corona segments are much shorter and erect. Despite overall similarities, it appears that these two species may not be close relatives (M. Fishbein et al. 2018).
The somewhat cruciform distribution of Asclepias hallii is odd and may be relictual. It extends from the eastern slope of the Rocky Mountains in Colorado west to the ranges of central Nevada, and from the Wasatch Range in northern Utah south to the Sierra Ancha in central Arizona. The species is fairly common at lower elevations of the Rocky Mountains in Colorado, particularly on the eastern slope, but is quite rare across the rest of its range, and it is considered to be of conservation concern in Utah. There are few documented occurrences in Arizona (Coconino, Gila, and Navajo counties), Nevada (Elko, Eureka, Lander, and White Pine counties), and New Mexico, where it has been documented by only a single specimen from Colfax County and may be extirpated. Its conservation status in these states merits evaluation. Asclepias hallii appears not to have been collected in Wyoming since 1958 and has been presumed to be extirpated; however, there is recent photo documentation from Albany County.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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