Common Milkweed (Asclepias syriaca) is a tall, robust perennial in the Apocynaceae family that serves as the primary host plant for the Monarch butterfly — one of North America's most iconic migratory insects. Its large, spherical clusters of fragrant pink-purple flowers produce copious nectar, while its seed pods split open in autumn to release hundreds of seeds, each attached to silky white floss that floats on the wind like tiny parachutes.
• The single most important host plant for the Monarch butterfly (Danaus plexippus) — Monarchs lay eggs exclusively on milkweed species
• The silky seed floss (coma) was collected by the ton during World War II to stuff life jackets and flight suits — it is six times more buoyant than cork
• The genus name Asclepias honors Asclepius, the Greek god of medicine
• The species epithet "syriaca" means "of Syria" — a misnomer, as the plant is native to North America
• All parts contain toxic cardiac glycosides (cardenolides) that deter most herbivores but are sequestered by Monarch caterpillars as a defense against predators
Taxonomie
• Found from southern Canada (Ontario, Quebec) southward through the eastern United States to Georgia and west to the Great Plains
• Grows in old fields, meadows, prairies, roadsides, and disturbed areas
• Has been introduced to Europe as an ornamental and has become naturalized in some areas
• The genus Asclepias contains approximately 140 species, mostly native to the Americas
• Indigenous peoples used milkweed for food, fiber, and medicine for millennia
• First described by Linnaeus in 1753
Stems:
• Erect, stout, unbranched or sparingly branched, 1 to 3 cm thick
• Covered with short, soft, whitish hairs
• Contain milky white latex sap when broken
Leaves:
• Opposite (sometimes whorled), broadly ovate to elliptic, 10 to 25 cm long
• Smooth margins, prominent midvein
• Dark green above, paler and softly hairy beneath
Flowers:
• Dense, spherical umbelliform cymes (umbels), 4 to 8 cm across
• Each umbel contains 30 to 100+ individual flowers
• Petals pink-purple with reflexed tips and a central crown (corona) of five hoods
• Intensely fragrant — sweet, vanilla-like scent
• Blooms June to August
Fruit:
• Large, erect, spindle-shaped follicles (pods), 8 to 15 cm long
• Split open in autumn releasing flat seeds with silky white floss
• Each pod contains 50 to 200+ seeds
• Grows in old fields, meadows, prairie remnants, roadsides, and disturbed ground
• Prefers well-drained soils in full sun
• The primary larval host for Monarch butterflies (Danaus plexippus)
• Flowers are extremely important nectar sources for bees, butterflies, moths, and hummingbirds
• Over 450 insect species have been documented feeding on Common Milkweed
• Produces toxic cardiac glycosides that Monarch caterpillars sequester, making adult butterflies toxic to birds
• Spreads aggressively by rhizomes, forming large colonies
• Cold-stratify seeds for 30 days before spring sowing, or sow in autumn for natural stratification
• Prefers full sun and well-drained soil
• Tolerates poor, dry soils once established
• Space plants 30 to 60 cm apart
• Spreads by rhizomes — can be aggressive in small gardens; contain with barriers or grow in meadow settings
• Do not use pesticides on or near milkweed — they kill Monarch caterpillars
• Hardy to approximately -35°C (USDA Zone 3)
Anecdote
During World War II, schoolchildren across the United States were recruited to collect milkweed seed pods. The buoyant, silky floss inside was used as a substitute for kapok in military life jackets — over 2.5 million pounds of floss were collected. A single seed pod contains enough floss to fill one life vest. The floss is also being researched today as a hypoallergenic filling for pillows and comforters, and as an absorbent material for oil spill cleanup.
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