Asclepias lemmonii
Asclepias hallii
big-leaf milkweed, Lemmon's milkweed
Hall's milkweed
1–3, erect to ascending, unbranched, very stout, 100–150 cm, densely hirsute, 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, petiolate, with 1 stipular colleter on each side of petiole;
petiole 1–5 mm, hirsute;
blade oval or oblong to ovate, 7–22 × 3–14 cm, subsucculent, base truncate to subcordate, margins entire, apex obtuse to truncate or emarginate, mucronate, venation brochidodromous, secondary veins nearly orthogonal, surfaces hirsute, margins ciliate, 8–16 laminar colleters.
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, paired, and extra-axillary, pedunculate, 21–53-flowered;
peduncle 6–13 cm, densely hirsute, 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.
13–22 mm, densely hirsute.
16–28 mm, densely pilose to tomentulose.
erect to pendent;
calyx lobes lanceolate, 3.5–6 mm, apex acute, hirsute;
corolla cream to greenish cream or ochroleucous, sometimes tinged pink, lobes reflexed with spreading tips, elliptic, 9–11 mm, apex acute, glabrous;
gynostegial column 0.5–1 mm;
fused anthers greenish brown, cylindric, 2.5–3 mm, wings right-triangular, closed, apical appendages oval;
corona segments cream to ochroleucous, sometimes tinged pink, shiny, subsessile, conduplicate, 6–8 mm, equaling or exceeding style apex, apex truncate, spreading and tapering, glabrous, internal appendage laterally compressed, erect, barely exserted, glabrous;
style apex shallowly depressed, green or pink.
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, 6–7 × 4–5 mm, margin winged, faces minutely rugulose;
coma 4–4.5 cm.
narrowly ovate, 6–7 × 4 mm, margin winged, faces and wings rugulose;
coma 2.5–3.5 cm.
erect on upcurved pedicels, lance-ovoid, 9.5–13.5 × 2–3 cm, apex attenuate, smooth, densely hirsute.
erect on upcurved pedicels, lance-ovoid, 8–12 × 0.7–1.5 cm, apex acuminate, smooth, pilosulous.
Asclepias lemmonii
Asclepias hallii
A highly distinctive species, Asclepias lemmonii just barely enters the United States in southern Arizona (Cochise, Pima, and Santa Cruz counties), where it inhabits canyons in pine-oak clad sky-island ranges. Asclepias elata is a common co-inhabitant of these canyons. Asclepias lemmonii has been documented from the Baboquiviri, Chiricahua, Huachuca, and Santa Rita mountains, and it is not common in any of these. It is considered to be of conservation concern in Arizona. The large, hirsute leaves with nearly orthogonal venation and robust, hirsute stems of A. lemmonii are unmatched among American milkweeds. Plants may reach heights over 2 m in the main range of the species in the northern Sierra Madre Occidental.
(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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