FAMILY: Asclepiadaceae—the Milkweed Family
The Asclepiadaceae is a family of succulent plants with milky sap. The milkweeds, which are known to most residents of the state, have a highly specialized flower, only briefy described here. The staminal filaments are basally fused into a tube, united to the corolla tube, and bear a whorl of appendages, collectively called the corona. The pollen of each anther is aggregated into a waxy mass, the pollinium. The ovary is superior, composed of 2 carpels, free at the base but fused at the apex into a common stigma; fruit: a pair of follicles, or 1 by abortion; seeds: flat, winged, with a tuft of hairs; leaves: opposite or whorled, simple, entire, without stipules; inflorescence: cymose, often appearing umbelliform; flowers: bisexual, 5-merous.
PHENOLOGY: The milkweeds generally flower June through August. A few species flower slightly earlier or extend slightly later into the season.
DISTRIBUTION: Some milkweeds are plants of wet places, swamps and bogs, others live in dry, rocky soil, while still others are weeds of cultivated fields, roadsides, pastures, and waste places.
PLANT CHARACTERISTICS: Those characteristics provided in the family description will identify the milkweeds. Generally the genus may be divided into those plants with narrow, lanceolate leaves and those with broad leaves and nearly parallel margins.
POISONOUS PARTS: The entire plant is considered poisonous.
SYMPTOMS: Toxicosis includes depression, weakness, staggering, tetanic seizures, elevated temperature, respiratory difficulties, dilated pupils, coma, and death. Postmortem: gross lesions: congestion of lungs, liver, and kidneys; acute catarrhal gastroenteritis; terminal dilitation of the heart ventricles; signs of central nervous system involvement, and atonic crop and gizzard in fowl; histological lesions: some cellular degeneration, especially of the kidney, may be apparent.
POISONOUS PRINCIPLES: The agents responsible for toxicity are not fully characterized, but toxic resinoids, cardioactive glycosides, and other components are suspected. The milky latex, upon contact, may elicit an allergic reaction in some sensitive individuals.
CONFUSED TAXA: Most people readily recognize milkweeds; the plants superficially resemble dogbane (see Apocynum).
SPECIES OF ANIMALS AFFECTED: Turkey, chickens, sheep, goats, cattle, and horses are susceptible to milkweed toxins. Humans are also poisoned by the plants.
TREATMENT: ( 11a)(b); (26)
OF INTEREST: Historically, several species of milkweed have been used for medicine, including Asclepias tuberosa L. and A. syriaca L. They contain asclepiadin, asclepion (a bitter principle), tannin, and volatile oil.