Montana Field Guide

Plants: Perennial, shallowly fibrous-rooted with a little-branched crown; stems mostly simple, sometimes a few (McGregor et al. 1986), 30–60 cm; herbage glabrate to puberulent (Lesica 2012).

Leaves: Usually 3-6 at each node, sessile, spreading, whorled (verticillate), subverticillate (McGregor et al. 1986) or closely alternate (Lesica 2012); blades long and threadlike to linear (McGregor et al. 1986), 2–6 cm in length (Lesica 2012), 0.5-1.5 (3) mm in width, usually leathery (coriaceous), smooth to puberulent (with small hairs barely visible), base and apex both narrowly acute, margins turned under (revolute) (McGregor et al. 1986).

Inflorescences: Few to numerous in the higher leaf axils (McGregor et al. 1986) consisting of umbels of 6 to 20 flowers; peduncles 1–4 cm long (Lesica 2012); pedicels threadlike with minute hairs, 5-11 mm in length (McGregor et al. 1986).

(Lesica's contribution adapted from Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX)

Flowers June-September (McGregor et al. 1986).

Sandy, clayey, or stony soil of grasslands, badlands, floodplains, and woodlands (Lesica 2012; McGregor et al. 1986).

(Lesica's contribution adapted from Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX)

North America is home to over 100 milkweed species. Monarch conservation groups have listed priority species for each U.S. region. Information pertaining to all aspects of North American monarch (Danaus plexippus) conservation can be found on the Monarch Joint Venture website.

Quality monarch butterfly habitat must have native milkweed species. Female monarchs only use milkweed plants to lay their eggs on, and monarch larvae must have milkweed to survive. Monarch habitat is supported when native milkweed species are planted or encouraged to grow. Monarchs do visit sites with only a few milkweed plants. However, larger habitats decrease the density of monarchs per plant. This has the potential to reduce both larval competition for food and the spread of disease. Milkweed nectar also nourishes a diversity of pollinators, including other butterflies, honeybees and moths (Willson et al. 1979).

POLLINATORS
The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus vagans, Bombus huntii, Bombus rufocinctus, Bombus ternarius, Bombus terricola, Bombus pensylvanicus, Bombus bimaculatus, Bombus griseocollis, Bombus impatiens, Bombus insularis, and Bombus flavidus (Plath 1934, Heinrich 1976, Thorp et al. 1983, Colla and Dumesh 2010, Colla et al. 2011, Koch et al. 2012, Williams et al. 2014, Tripoldi and Szalanski 2015).

Flowers: Flowers 5–8 mm high; sepals 1–3 mm long, pubescent (Lesica 2012), green or shaded with purple (McGregor et al. 1986); petals greenish-white, purple-tinged, 2–5 mm long, glabrous (Lesica 2012), oval and reflexed (McGregor et al. 1986); gynostegium greenish-white or purplish, glabrous, column ca 1.5 mm high (Lesica 2012), 0.5-0.8 mm in width, nearly cylindric (McGregor et al. 1986); hoods oblong, 1–2 mm long (Lesica 2012); horns clearly exserted and arching over the anther head; corpusculum ca 0.2 mm in length; pollinia ca 1 mm in length. Follicles on curved to straight stalks (McGregor et al. 1986), ascending to erect, fusiform, smooth, puberulent, 8–10 cm long (Lesica 2012).

Fruit: Seeds 5-6 mm in length, broadly egg-shaped, with a tuft of soft white hairs (coma), 2.5-3.5 cm in length (McGregor et al. 1986).

(Lesica's contribution adapted from Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX)

This species is toxic to farm animals (McGregor et al. 1986).

ECONOMIC VALUE
Milkweed populations provide nourishment and habitat to pollinators (Monarch Joint Venture 2015; Willson et al. 1979), which supports agricultural crops that also require insect pollination (Nabhan & Buchmann 1997), improves fruit conditions for market (Garratt et al. 2014), raises the nutritional value of certain foods, (Bommarco et al. 2012), and sustains various levels of the food web (Gilgert and Vaughan 2011).

Asclepias verticillata is recommended for planting in order to develop habitat for the Monarch Butterfly (Monarch Joint Venture 2015) and to improve pollinator habitat for raising agricultural crops.