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Asclepias Linnaeus. Subfamily: Asclepiadoideae. Milkweed.

Key to Asclepias

A genus of about 400 species, herbs (mostly perennial) and shrubs, temperate and tropical, of North America, Central America, South America, West Indies, Africa (Fishbein 2023; Endress et al. 2018).

Key advice:The flowers of Asclepias have an unusual structure and associated terminology that is necessary for successful interpretation of the key. From the bottom of each flower, there is first a whorl of 5 sepals, almost always green or greenish. Next is a whorl of separate petals, in most species recurved, and variously colored (brightly, or in quite a few species green, greenish white, yellowish green, or green flushed with rose or purple). Next inmost is the corona, a pentamerous structure of 5 hoods and 5 horns (these are petaloid appendages attached to the stamens). At the center is the gynostegium, a fusion of the stigmatic disc (innermost of all) and the 5 anthers. An insect leg passes through the stigmatic slit between two adjacent anthers, and can pick up the two pollinia, attached to one another by two translater arms, fused at the corpusculum.

Ref: Endress et al. (2018) In Kadereit & Bittrich (2018); Farmer & Bell (1985); Fishbein (2023a) In Flora of North America Editorial Committee (2023c); Fishbein et al. (2011); Turner (2009b); Woodson (1954). Show full citations.

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image of plant© Alan Cressler: Asclepias asperula, Rain Valley, Cochise County, Arizona 2 by Alan Cressler | Asclepias asperula ssp. capricornu source | Original Image ⭷
image of plant© Alan Cressler: Asclepias pumila, Devils Tower National Monument, Crook County, Wyoming 2 by Alan Cressler | Asclepias pumila source | Original Image ⭷
image of plant© Alan Cressler: Asclepias texana, Can Canyon, Lost Maples State Natural Area, Bandera County, Texas 2 by Alan Cressler | Asclepias texana source | Original Image ⭷
image of plant© Alan M. Cressler | Asclepias obovata | Original Image ⭷
image of plant© Alan M. Cressler | Asclepias perennis | Original Image ⭷


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