Endangered Plants of Ontario

Rare Plants of Ontario

Poke Milkweed

Asclepias exaltata

Status

Rare in Ontario and British Columbia; endangered in Indiana, rare inArkansas, Iowa, and Louisiana.

Range

Southern Maine across southern Ontario to Minnesota, south to Georgia and Iowa.

Habitat

Rich deciduous woods.

Height

0.5 to 1.5 m.

Bloom Period

Summer

Factors contributing to its status

Poke milkweed is a species of the Carolinian forest, at the northern limit of its range in southern Ontario.

Clearing of the forests has greatly reduced its habitat.

Notes

Milkweed flowers exhibit remarkable adaptations for pollination. Nectar is produced in cups on the filaments of the stamens.

When a bee forages on the flower cluster, one of its legs is likely to slipinto one of the narrow grooves between the anthers. This brings it into contact with a sticky clamp; when the bee flies away, the clamp adheres to its leg, trailing two attached pollen masses. When the bee visits another flower, the pollen masses break away from the clamp and adhere to that flower's sticky stigma. (Occasionally milkweed flowers act as leghold traps, when insects are unable to pull the pollen masses from the flowers.)

Despite this elaborate pollination mechanism, the many flowers in a milkweed flower cluster generally produce only one to four pods: growth of additional pods is inhibited once the first few pods begin to develop. Each pod, however, contains many seeds, each with the familiar feathery appendage that is readily caught by the wind.

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Habitat	Rich deciduous woods.
Height	0.5 to 1.5 m.
Bloom Period	Summer
Factors contributing to its status	Poke milkweed is a species of the Carolinian forest, at the northern limit of its range in southern Ontario. Clearing of the forests has greatly reduced its habitat.
Notes	Milkweed flowers exhibit remarkable adaptations for pollination. Nectar is produced in cups on the filaments of the stamens. When a bee forages on the flower cluster, one of its legs is likely to slipinto one of the narrow grooves between the anthers. This brings it into contact with a sticky clamp; when the bee flies away, the clamp adheres to its leg, trailing two attached pollen masses. When the bee visits another flower, the pollen masses break away from the clamp and adhere to that flower's sticky stigma. (Occasionally milkweed flowers act as leghold traps, when insects are unable to pull the pollen masses from the flowers.) Despite this elaborate pollination mechanism, the many flowers in a milkweed flower cluster generally produce only one to four pods: growth of additional pods is inhibited once the first few pods begin to develop. Each pod, however, contains many seeds, each with the familiar feathery appendage that is readily caught by the wind.