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Family: Asclepiadaceae Borkh.

Kingdom: Plantae Rank: Family Parent: Gentianales Status: Valid

Common Names:

  • MILKWEED FAMILY - English, United States of America

Morphological Description

Family Recognition in the Field: Herbs or vines usually with milky sap, frequently opposite leaves, flowers with a distinctive corona and a gynostegium (= combined structure composed of stamens and pistil), and wind-dispersed seeds with a tuft of long silky hairs. Similar to Apocynaceae (e.g., herbs or vines with milky sap and often opposite leaves) but that family has flowers without corona or gynostegium.

Diagnosis: Ours perennial herbs or twining vines, usually with milky juice; leaves usually opposite or whorled or alternate, simple, entire or undulate; flowers axillary or terminal, solitary, in umbels, or umbel-like racemes; calyces deeply 5-lobed; corollas deeply 5-lobed; crown (= corona) of various sorts (e.g., disk-like, inflated, flat, stamen-like-often called hoods; sometimes very conspicuous) present around base of the short stamen-tube; stamens 5, the filaments united (except in Periploca), the anthers large, united to form an anther head enclosing the two pistils (the combined column-like or disk-like structure made up of the stamens and pistils is called the gynostegium); anthers usually with a terminal outgrowth of the connective called an anther appendage and with lateral wing-like margins (= anther wings); anther wings from adjacent anthers are positioned close together and thus form a slit-like opening or groove between them (through which the legs or other appendages of pollinators can fit); pollen grains coherent in a mass (= pollinium) (except in Periploca); the 2 pollinia from adjacent anthers connected by a wishbone-shaped structure (= translator); clip-like portion (= corpusculum) of translator attaches the pair of pollinia to the pollinator's appendage as it is pulled out of the groove between adjacent anthers (pollinia from other flowers can enter the groove and thus be brought into contact with the enclosed stigmatic surfaces); pistils 2, united only by styles and/or stigmas; fruit of follicles; seeds numerous, usually comose.

Other

Ecology: Some species are toxic in nature.

Notes: A large (2,900 species in 315 genera), mainly tropical and warm area family with a few in temperate regions; it consists of herbs to shrubs, trees, vines, and cactus-like succulents; the family contains a number of ornamentals including Hoya (WAX PLANT) and Stapelia (CARRIONFLOWER -with flesh-like, foul-smelling flowers that attract carrion flies which serve as pollinators). There are laticifers throughout and the milky sap often contains alkaloids or other toxins such as glycosides; as a result they are avoided by most animals. However, members of the Danaidae (milkweed butterflies such as the monarch) as larvae feed primarily on members of the Asclepiadaceae and as a result are distasteful to predators (Howe 1975) due to the sequestered toxins. Asclepiadaceae typically have a specialized insect pollination mechanism in which the pollinia become attached to the legs of insects which have been guided into position by grooves or slits in the gynostegium (Macior 1965; Bookman 1981); some species have extremely unpleasant odors (carrion smells) and are pollinated by flesh-flies. The MILKWEEDS are closely related to the Apocynaceae and appear to represent a clade within that family (the relationship can be seen in the shared milky sap and pistils united only by styles and/or stigmas). From a cladistic standpoint the two families should be lumped to form a more inclusive monophyletic Apocynaceae (Judd et al. 1994); Liede (1997), for example, treated the family as subfamily Asclepiadoideae in the Apocynaceae. (subclass Asteridae)