Horsetail Milkweed

Asclepias subverticillata

Horsetail Milkweed, Asclepias subverticillata, photo © by Mike Plagens

In open ponderosa woodland near the headwaters of the East Verde River, Gila Co., Arizona, USA. 21 Aug. 2010. A pair of red and black Milkweed Bugs (Lygeaus kalmii) can be seen as well as a small geometrid moth.

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FLOWERS: Bright white flowers are conspicuously five pointed and set in umbels of a dozen or so flowers. A flurry of insects are often present to take nectar.

LEAVES: The leaves are very narrow - almost grass-like. Two or three such leaves are set at each stem node, thus another common name, Whorled Milkweed.

PERENNIAL HERB: Typically regrowing for several years up to a height of 1 m. Stem breaks ooze milky latex which is poisonous. Livestock can be poisoned by eating this plant rendering still another common name, Poison Milkweed.

RANGE: Fairly common on mostly disturbed sites in the ponderosa zones of Arizona New Mexico and Colorado. Also among piñon-juniper.

FRUIT: Paired turgid fruits develop from each flower after pollination. The many seeds inside have copious white hairs.

UNARMED. No spines or prickles.

Asclepiadaceae -- Milkweed Family

Look for one or more kinds of milkweed bugs in addition to all the flower visitors. Ocassionally dense colonies of yellow aphids will be on emerging shoots and buds.

Large Milkweed Bug   Small Milkweed Bug  Oleander Aphid

More Information:

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Arizona Naturalists
Arizona's Ponderosa Woodlands
The Flora of Arizona's Ponderosa Woodlands


Copyright Michael J. Plagens, page created 18 August 2011,
updated 9 Aug. 2016.