Milkweed flowers rival orchids in complexity and can trap insects too small to escape
Milkweed doesn't scatter loose pollen. It packs it into paired sacs that clip onto a visiting insect's leg when it slips into a slit in the flower. A strong bee pulls them free and carries them off; a weaker visitor may stay stuck and die. Monarch caterpillars, meanwhile, depend on these toxic plants to grow.
Asclepias is a genus of more than 200 perennial species spread across Africa and the Americas, a dozen of them in South America. The common name comes from the milky latex that oozes from damaged tissue. That sap contains cardenolides, heart-affecting compounds that make most species poisonous to people and many animals. The group once had its own family but now sits as a subfamily within the dogbanes.
Each flower folds five petals backward to expose a central column ringed by a corona of five hoods, each sheathing a curved horn; the shape and colour of these parts help botanists tell species apart. Between the hoods lie glands holding the pollen sacs, known as pollinia. Pollination runs in reverse when a carried sac lodges inside another flower's slit. Bees and wasps do more than half the work. Monarch butterflies, for all their fame, are poor pollinators, and introduced honey bees often get trapped and die.
Seeds ripen in pods called follicles. When they split, each seed drifts away on a tuft of silky white hairs, the coma, sometimes called floss or silk, and some species also spread by cloning. Besides feeding native bees with nectar, milkweeds host a specialised crowd of beetles, moths and true bugs that tolerate their chemical defences, and they are essential larval food for monarchs.
Where the genus name comes from is murkier than it looks. In the first century AD, Dioscorides and Pliny the Elder each described a plant called asclepias, usually traced to the healing god Asklepios, though neither writer mentions him. Their plant is often identified as what is now Vincetoxicum hirundinaria, though some botanists dispute it. Linnaeus set up the genus in 1737 and named 18 species in 1753; seven have since been moved to other genera, including that very Vincetoxicum.
Source: Asclepias
