Asclepias verticillata L.

Whorled Milkweed


CC = 2
CW = 5
MOC = 82

© SRTurner

Family - Asclepiadaceae

Habit - Perennial forb from a fibrous rootstock and rhizomes.

Stems - Ascending to erect, to 60 cm, occasionally few-branched toward the tip and with axillary branchlets with pairs or clusters of leaves absent, short-hairy in longitudinal lines, with white sap, with numerous nodes and short internodes.

Asclepias_verticillata_stem2.jpg Stem and leaves.

© SRTurner

Leaves - Mostly in whorls of 3-6, sessile or short petiolate. Leaf blades 2-8 cm long, 0.5-2.5 mm wide, linear, the base narrowed or tapered, the tip sharp pointed, the margins revolute, glabrous or sparsely and minutely hairy, with single prominent midrib.

Asclepias_verticillata_leaves.jpg Leaves.

© DETenaglia

Inflorescence - Axillary pedunculate umbels, 2-10 per stem. Peduncles to 3 cm long, pubescent. Flowers typically 6-20 per umbel. Pedicels purplish at base, 8-9 mm long, pubescent. Bracts usually present at the base of the umbels, these linear and short.

Asclepias_verticillata_inflorescence2.jpg Buds and inflorescences.

© SRTurner

Asclepias_verticillata_inflorescence.jpg Inflorescences.

© DETenaglia

Flowers - Calyx lobes 5, reflexed, glabrous or sparsely short-hairy, 1.5-2.5 mm long, narrowly lanceolate to ovate. Corolla lobes 5, reflexed, glabrous, white to pale green (usually with age), often pale purplish at apex, 3.5-5.0 mm long, elliptic. Gynostegium appearing stalked (the column visible below the bases of the hoods), pale green to white, the corona slightly shorter than to about as long as the tip of the anther/stigma head. Corona hoods white, 1.5-2.0 mm long, erect, attached toward their bases, broadly oblong in outline, the tips broadly rounded, the margins not toothed, the bases not pouched. Horns white, attached near the hood bases, extended conspicuously beyond the tips of the hoods and incurved over the anther/stigma head, linear, not flattened, tapered to a sharp point at the tip. Anther column greenish, white at apex, 2 mm long. Pollinia 1.2 mm long, translator deep purplish-brown. Pistils 2, glabrous, greenish, 2 mm long.

Asclepias_verticillata_flowers3.jpg Flowers.

© SRTurner


© SRTurner

Fruits - Follicles 7-10 cm long, erect or ascending from erect to deflexed stalks, narrowly elliptic-lanceolate in outline, the surface smooth, glabrous or minutely hairy. Seeds with the body 5-6 mm long, the margins narrowly to somewhat more broadly winged, the terminal tuft of hairs white.

Flowering - May - September.

Habitat - Prairies, glades, bluffs, pastures, open woods, roadsides, railroads.

Origin - Native to the U.S.

Lookalikes - A. stenophylla.

Other info. - This attractive little species can be found throughout most of Missouri, and throughout most of the continental U.S. except for a few far western states. It is often seen, sometimes in large populations, in freeway medians. Like most of the species in this family the plant has a white sap which is irritating and toxic. This is an easily recognized members of the genus due to its very narrrow, whorled leaves. At a glance it could be mistaken for the much less common A. stenophylla, but that species has far fewer leaf nodes, which are not whorled and are usually alternate. Because it handles dry conditions very well, A. verticillata would make a fine garden specimen. Many flying insects are attracted to its flowers.

Photographs taken at the "Narrows", Oregon County, MO., 6-28-03 (DETenaglia); also at Holly Ridge Conservation Area, Stoddard County, MO, 5-20-2014, and Onondaga Cave State Park, Crawford County, MO, 6-18-2014 and 6-24-2014 (SRTurner).