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Asclepias tuberosa (butterfly weed, butterfly milkweed)

Asclpeias tuberosa
Asclepias tuberosa in a ditch in southern Indiana

 

The first time we found this stunning milkweed we were traveling across southern Indiana on Interstate 64, watching clusters of orange-flowered plants in the ditches zoom by. Fortunately, when we could no longer take it and had to pull over, there were several plants on the un-mowed embankment of an exit ramp, making an ooo-and-ahh photography stop slightly less dangerous.

Asclepias tuberosa, often called butterfly milkweed, or just butterfly weed, has "typical" milkweed flowers with 5 peeled-back petals (labeled "A" in the illustration below and to the right), 5 "hoods" (B), and 5 "horns" (C). The flowers are grouped together in slightly rounded-topped clusters—and in Asclepias tuberosa the clusters often spread out laterally.

Range of Asclpeias tuberosa

midwestern range

There are some decidedly non-milkweed-ish features of Asclepias tuberosa, however, beginning with the lack of milk; broken leaves and stems do not exude a white latex. Additionally, the leaves alternate on the stem (in most milkweeds they are opposite)—and, if you were to dig up the plant (please don't) you would find a long, knobby taproot (the tuber in the scientific name tuberosa).

Butterfly milkweed grows to about 2.5 feet high. Its dark green leaves are narrowly oblong, tapering to a point; they have very short petioles and are slightly fuzzy. The stem is light green and hairy, becoming reddish with age. The flower buds are initially light green with hints of orange; as the flowers open the deep orange color develops. Seed pods are long, slightly hairy, and slender.

Asclpeias tuberosa
flower buds

 

Asclpeias tuberosa
developing flowers

 

Asclpeias tuberosa
mature flowers


Asclpeias tuberosa
leaves mostly alternating; stem hairy

 

Asclpeias tuberosa
rounded flower clusters that often group horizontally

Asclpeias tuberosa
narrowly oblong leaves tapering to a point; very short petioles; upper surface bald; lower surface slightly fuzzy


Asclepias tuberosa seed pod
seed pod

 

Asclepias tuberosa seed pod
young seed pod

Cycnia inopinatus caterpillar
Cycnia inopinatus (unexpected Cycnia) caterpillar


Caterpillars of Cycnia inopinatus, the "unexpected Cycnia," are especially fond of Asclepias tuberosa foliage, and their orange colorations make them hard to see against the flowers. The adult moths, which we have not seen, are whitish.



References: Jones 1971, Jones 2005, Horn2012, Voss & Reznicek 2012, Kurz 2014, Mohlenbrock 2014, Lotts & Naberhaus 2017, Hilty 2017, USDA 2017.


Kuo, Michael & Melissa Kuo (July, 2017). Asclepias tuberosa (butterfly weed, butterfly milkweed). Retrieved from the midwestnaturalist.com website: www.midwestnaturalist.com/asclepias_tuberosa.html

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