Butterfly-weed and other Milkweeds

Milkweeds in the genusAsclepias are one of the joys of summer. One of the most beautiful and easily recognizable species is the orange milkweed or butterfly-weed (Asclepias tuberosa). There are 10 other species of milkweed in our area through the northern Blue Ridge Mountains (summarized in the chart, below, with the taxonomic changes in milkweeds.) All of the milkweeds are native, summer-blooming perennials that have wide ranges of distributions in the eastern U.S.  Butterfly-weed is found in dry, sunny fields, along road sides, and at edges of woods from Eastern Canada and Maine to Florida and west to Ontario through most of the southwestern states (even California and North Dakota.)  According to the Digital Atlas of Virginia Flora, it is found in all counties of Virginia.

All milkweed species were formerly placed in the Asclepidaceae (milkweed family) but now this family is included in the Apocynaceae (dogbane family). The genus name Asclepias is derived from the name of the Greek god Asclepius, the god of medicine and healing referring to the medicinal properties of various species of milkweeds. The species epitaph (name) tuberosa refers to the tuberous roots of these plants. (The derivation of species epitaphs of other species in our area are summarized in the chart of listing these species. None of the scientific names of the milkweeds in our area have been changed in the Flora of Virginia.) The common name butterfly-weed refers to the fact it often attracts butterflies [as well as bees and other insects] as pollinators and is the host plant for the larvae of monarch and queen butterflies. Other common names for A. tuberosa are orange for the color, pleurisy root for its medicinal use, and chigger-flower referring to chiggers often found near the plants, although there is no proof that one will contract chiggers from being on the plants. Common names of the other species of milkweed are included in the chart summarizing the ones in our area.

Butterfly-weed is the only species of milkweeds in our area that does not exude a milky sap when damaged.  The plant stands up to three feet tall with alternate oblong leaves that are 3-4 inches long.  All other milkweeds in our area have opposite leaves. The taproot of butterfly-weed can be up to 20 feet long with many tuberous projections.

Milkweeds have a very unusual flower structure: A calyx of 5 reflexed sepals fused at bases, a corolla of 5 reflexed petals fused at bases, 5 stamens that are attached at the base of the corolla. The filaments of the stamens are petal-like and form a corona or crown made up of 5 scoop-like hoods, each with a horn-like structure inside. The corona encloses the stigma or upper parts of the compound pistil formed by two carpels (female parts of flower). The anthers of the stamens stick to the stigmas of the pistils forming a gynostegium. The pollen grains in the anthers adhere together to form a mass or bag-like structure known as pollinia. Each anther has two parts that each produces a pollinium and the pair of pollinia is attached to each other by appendages or translator arms that have a sticky pad or corpusculum at the top, collectively forming a pollinarium. There are two carpels that form a compound pistil. The ovary of each carpel is separate each with a short neck or style with the two stigmas fuse to form a stigmatic disk. The stigmatic head is five-angled with glands that adhere to the corpusculum. There are stigmatic slits in the gynostegium that lead to the pollinaria. The pollinator such as a butterfly or bee must slip a leg through one of these slits and snag a pollinarium that adheres to the insect’s leg as it pulls out its leg. The pollinator must then visit another flower of the same species and repeat the process to stuff the pollinarium into its gynostegium slit.  Each pollinium has many pollen grains so if fertilization of an ovary occurs many seeds (up to 200) are produced that are enclosed in the fruit or follicle or pod. Pollination rates are not high as one might expect. Each flattened seed has a silky appendage or coma that assist in dispersing the seeds when the follicle or pod splits open and the seeds float in the wind.  During WWII, American school children collected over 5 tons of milkweed seeds with comas that were used to stuff lifejackets when kapok was not available. These comas are still used to stuff hypoallergenic pillows.

The medicinal and edible uses of butterfly-weed and other milkweeds are many. Historicalmedicinal uses of butterfly-weed included treating lung inflammation of pleurisy and asthma, swelling from rheumatism, and eliminating intestinal worms. It has been used as a diuretic and laxative as well as serving as a principle ingredient in Lydia E. Pinkham’s Vegetable Compound used to treat “female problems” of menstrual cramps and menopause. The early shoots and flower buds of this and other species are edible but require preparation with several changes of water.

This summer enjoy the beauty of butterfly-weed and other milkweed species as well as the variety of pollinators that visit these interesting plants. This fall observe the interesting pods of milkweeds and watch the wind disperse their seeds.

Websites great for milkweed flower structure:

BackyardNature: Milkweed Flowers

A Neotropical Savanna: Milkweed Flower (Stigmatic Column)

Chart of milkweed species in our area