Asclepias lemmonii
Asclepias elata
big-leaf milkweed, Lemmon's milkweed
nodding milkweed
1–3, erect to ascending, unbranched, very stout, 100–150 cm, densely hirsute, not glaucous, rhizomes absent(?).
1 (rarely 2 or 3), erect, unbranched, 30–80 cm, glabrous, 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.
opposite, sessile, with 1 inconspicuous stipular colleter on each side of leaf base;
blade oval or elliptic to oblong or lanceolate, 5.5–14 × 1.5–6 cm, subsucculent, base cordate, clasping, margins sometimes crisped, apex rounded to acute, mucronate, venation brochidodromous, surfaces glabrous, glaucous, margins minutely and remotely ciliate, laminar colleters absent.
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.
terminal and extra-axillary at upper nodes, pedunculate, 7–20-flowered;
peduncle 5–20 cm, pilosulous in a line, glaucous, with 1 caducous bract at the base of each pedicel.
13–22 mm, densely hirsute.
20–32 mm, pilosulous, often in a line.
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.
pendent;
calyx lobes elliptic to oval, 5–8 mm, apex acuminate, sparsely pilosulous to glabrate;
corolla green, lobes reflexed with spreading tips, oval, 11–14 mm, apex acute, glabrous;
gynostegium sessile;
fused anthers green, obconic, 3–3.5 mm, wings narrowly right-triangular, thick, open just above base, apical appendages lanceolate;
corona segments white, yellow to tan dorsally, subsessile, conduplicate, 4–6 mm, equaling style apex, apex truncate, glabrous, internal appendage a crest, included in segment, glabrous;
style apex depressed, green to greenish cream.
ovate, 6–7 × 4–5 mm, margin winged, faces minutely rugulose;
coma 4–4.5 cm.
ovate to lanceolate, 6–7 × 3–6 mm, margin winged, sometimes minutely erose, faces rugulose;
coma 4–4.5 cm.
erect on upcurved pedicels, lance-ovoid, 9.5–13.5 × 2–3 cm, apex attenuate, smooth, densely hirsute.
erect on upcurved pedicels, fusiform to lance-ovoid, 8–13 × 1–2 cm, apex long-attenuate, smooth, pilosulous.
Asclepias lemmonii
Asclepias elata
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 elata is one of the few milkweeds in the flora area that possesses a mostly Mexican distribution but does not belong to the major clade that contains most of such species (species 23–27 here). Rather it is the sole representative in the flora, and the most northerly distributed member, of a small clade of glaucous, vegetatively homogeneous species ranging as far south as Costa Rica (M. Fishbein et al. 2011). Asclepias elata has been inconsistently recognized as distinct from A. glaucescens since the time of A. Gray et al. [1878–1897, vol. 2(1)]. However, at least since J. N. Rose (1892), the distinction between these species has been understood, and was presented clearly by R.E. Woodson Jr. (1954). Although indistinguishable in the absence of flowers, A. elata differs by fully pendent (versus erect to pendent) flowers, fewer flowers per umbel, longer corolla lobes, and corona segments that spread away from the gynostegium and are exceeded by the style apex, with the appendage merely a crest included in the segment (versus segments that are strict, overtop the style apex, and bear exserted appendages in A. glaucescens). Both species have extensive distributions, but they are largely allopatric, except in Mesoamerica. The northernmost populations of A. glaucescens are in Nayarit and San Luis Potosí. Asclepias elata is one of a cohort of species reaching their northwestern limits in Arizona that indicate biogeographic affinity of that region to the eastern slope of the Sierra Madre Occidental and Altiplano, rather than the western slope of the Sierra Madre Occidental. Other examples from the milkweed flora include A. brachystephana, A. involucrata, A. nummularia, A. oenotheroides, and A. quinquedentata. In Arizona, A. elata is known from Cochise, Graham, Pima, and Santa Cruz counties, in New Mexico from Eddy, Hidalgo, and Sierra counties, and in Texas from Brewster, Culberson, Jeff Davis, and Presidio counties.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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