Week 31: Butterfly Weed (Paul Muldoon, Nathaniel Lord Britton)
AUGUST 2ND, 2026
Cover Image. William Clark, “Asclepias tuberosa. Tuberous Swallow-wort.” From Richard Morris, Flora Conspicua: A Selection of the Most Ornamental Flowering, Hardy, Exotic and Indigenous Trees, Shrubs, and Herbaceous plants, for Embellishing Flower-Gardens and Pleasure-Grounds. London: Longman, 1826.
Waning Gibbous Moon; August Cross-Quarter Day
Headnote
I came to appreciate butterfly weed through my wife Meghan’s occasional summer pickings. The plant's clustered orange blooms can look like small flames or fireworks hovering above a meadow- or table-scape; or, if an especially long and narrow cluster is laying at rest on a table, it reminds me of a beaded brooch or hair clip.* But I didn’t know the wonder or the strangeness behind the plant’s namesake until more recently.
Butterfly weed (Asclepias tuberosa), known historically as pleurisy root, is a member of the perennial, herbaceous, flowering milkweed genus and is native to eastern and central North America. Unlike other milkweeds, which produce a milky latex that they release when damaged, butterfly weed runs a clear or greenish sap. But both substances are actually a powerful defense mechanism containing cardiac glycosides, which literally disrupt heartbeats; specifically, they inhibit the cellular sodium-potassium pump that regulates the muscle’s contractions. The poison is a family affair—milkweeds are part of the dogbane (Apocynaceae) family, some members of which were traditionally used to make the ends of darts and arrows deadly toxic. Nonetheless, milkweed sap also was used traditionally to clear warts and other skin conditions, and the plant’s roots were chewed for digestive or respiratory issues. Extracts of the root were included in the official U.S. Pharmacopeia for nearly a century, until the early twentieth century.
The monarch butterfly (Danaus plexippus) is not immune to this heart poison; its growth can suffer under the metabolic strain. Yet through a delicate balance cultivated over eons and regions, the famously beautiful insect has learned to handle and make use of it. In fact, milkweed is the only cradle a monarch will accept, and monarch caterpillars are incapable of digesting the leaves of any other plant. The female butterfly searches out milkweed's particular bitterness, often preferring milkier and more poisonous species over the showy butterfly weed, and lays her eggs on the underside of a leaf. When the eggs hatch, the caterpillars use special trenching and cutting techniques to divert the sap from the leaves, seeking to avoid not the sap’s poison but its stickiness, which can glue their mouths shut or adhere their bodies to the plant. Once the caterpillars grow larger and stronger, they actually make pools of the sap on the leaves and ingest it in large quantities, pirating the poison to make a defense mechanism of their own. The poison accumulated in their bodies renders the adult butterflies bitter and undesirable to potential predators, and it also inhibits the deadly parasite that plagues monarch butterflies. In fact, a butterfly infected with the parasite can seek out an especially toxic plant to be its nursery. "The dose makes the poison," as Paracelsus expressed.
The butterfly’s dependence on the milkweed--poison and all--drives its epic, multi-generational annual migration. Beginning in the coniferous forests of central Mexico, the initial “super generation” of monarchs travels north, timing its arrival in the southern U.S. with the first emergence of the milkweeds in this region. This generation lays its eggs and then dies, producing a new generation with a shorter lifespan that will move further north in pursuit of newly growing milkweeds. This cycle repeats several more times, each curtailed generation finding a fresh crop of poisonous plants, until the final generation reaches the north in autumn. The cooling temperatures and declining plant life trigger another “super generation” of monarchs, which pause their fertility to make the treacherous 3,000-mile journey back to Mexico, where the next generation will begin a new transcontinental quest for nourishment and poison.
* The plants produce wide, umbrella-shaped clusters of flowers (called umbels, from the Latin for “parasol”) from their axils (the spot where the stem of the leaf connects to the main stem of the plant).
Fig. 2. Monarch and Milkweed, by Helen Frost and Leonid Gore. Read Aloud by Reading Rhino (July 30, 2026).
Readings
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As he knelt by the grave of his mother and father
the taste of dill, or tarragon—
he could barely tell one from the other—
filled his mouth. It seemed as if he might smother.
Why should he be stricken
with grief, not for his mother and father,
but a woman slinking from the fur of a sea-otter
in Portland, Maine, or, yes, Portland, Oregon—
he could barely tell one from the other—
and why should he now savour
the tang of her, her little pickled gherkin,
as he knelt by the grave of his mother and father?
*He looked about. He remembered her palaver
on how both earth and sky would darken—
‘You could barely tell one from the other’—
while the Monarch butterflies passed over
in their milkweed-hunger: ‘A wing-beat, some reckon,
may trigger off the mother and father
of all storms, striking your Irish Cliffs of Moher
with the force of a hurricane.’
Then: ‘Milkweed and Monarch “invented” each other.’*
He looked about. Cow’s-parsley in a samovar.
He’d mistaken his mother’s name, ‘Regan’, for ‘Anger’:
as he knelt by the grave of his mother and father
he could barely tell one from the other.
Paul Muldoon. “Milkweed and Monarch.” The Annals of Chile. London: Faber & Faber, 1994. 10-11.
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Hirsute-pubescent; stems stout, simple, or branched near the summit, ascending or erect, very leafy, 1°-2° high, the milky sap scanty. Leaves alternate, lanceolate or oblong, acute or sometimes obtuse at the apex, narrowed, rounded or cordate at the base, sessile or short-petioled, 2’- 6’ long, 2”-12” wide; umbels cymose, terminal, many-flowered; peduncles shorter than the leaves; pedicels 1/2’-1’ long; corolla-segments about 3” long, greenish orange; corona-column about 1\2” long; hoods erect, oblong, bright orange, or yellow, 2-3 times as long as the stamens, longer than the filiform horns; fruiting pedicels decurved; follicles nearly erect, finely pubescent, 4’-5’ long.
In dry fields, Maine and Ontario to Minnesota, Florida, Texas, Chihuahua and Arizona. Consists of numerous races, differing in shape and size of the leaves and color of the flowers. June-Sept. Wind-or orange-root. Canada-, flux-, tuber- or white-root. Orange swallow-wort. Yellow milkweed. Indian-posy.
“Asclepias tuberosa L. Butterfly-weed or -flower. Pleurisy-root. Fig. 3383.” From Nathaniel Lord Britton and Addison Brown. An Illustrated Flora of the Northern United States, Canada and the British Possessions, Vol. III: Gentianaceae to Compositae (Gentian to Thistle). 1898. Second Edition. New York: Charles Scribner’s Sons, 1913. 25.
Supplementum
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Craig Holdrege. “The Story of an Organism: Common Milkweed.” The Nature Institute (2010).
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Helen Frost and Leonid Gore. Monarch and Milkweed. New York City, New York: Atheneum, 2006.
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Anurag Agrawal. [Monarchs and Milkweed: A Migrating Butterfly, A Poisonous Plant, and Their Remarkable Story of Coevolution](http://A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution). Princeton, New Jersey: Princeton University Press, 2017.
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Sandy Masuo, “Got Milkweed?,” The Huntington Library, Art Museum, and Botanical Gardens (October 18, 2022).
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Robert Frost, “Pod of the Milkweed.” 1954. Genius.com
Fig. 3. Craig Holdrege. Shoot development in common milkweed (Asclepias syriaca). Shoots from one colony, drawn to scale (Summer 2007).
✦ From the Earthly Book of Hours ✦
Not a lot new here this week, but I did find a lovely quote about boredom from Walter Benjamin (clipped below).
