Plant Profile: Milkweeds

By Craig Huegel

Reprinted from The Understory, Jan.–Feb. 1995

Editor's Note: Since this article was published, the family name of milkweeds has been changed from Asclepiadaceae to Apocynaceae.

Photo © Betty Wargo

Because milkweeds (Family Asclepiadaceae) are the larval food of monarch butterflies, there is great interest in them. Many also are attractive wildflowers that provide a source of nectar and color. Milkweeds are a diverse group in Florida and contain some very interesting species for the home landscape. Surprisingly, however, very few are available from plant nurseries and few are used. In fact, the most commonly seen milkweed is not a native, although frequently it is referred to as one. (A. curassavica) with its tall lanky growth and orange and yellow flowers is a staple of any butterfly garden. It works extremely well for this, but it has a tendency to spread if its seed pods are not removed before they open. I strongly urge our readers to discourage its use anywhere near natural areas unless it will be vigorously managed and controlled.

Milkweeds are easily recognized by their flowers, which have evolved both a complex structure and pollination strategy. A hood partially conceals the reproductive parts and the petals are partially fused and curve backwards, away from the hood. The flowers occur in clusters, called umbels. Flower color varies widely among species.

Pollinated flowers eventually turn into the characteristic seed pods which ripen, split open and release the flattened seeds. Each seed is attached to a tuft of silky hairs (called a coma) that carries it through the air-well beyond the parent plant. For this reason, milkweed plants usually occur as scattered individuals.

Most milkweeds also are characterized by a thick, milky sap. This sap contains complex alkaloids that make it toxic to eat. Milkweed butterflies, however, have evolved a digestive system that allows them to feed on these plants. The toxins do not harm the caterpillars, but they accumulate in their blood and make them distasteful and/or toxic to their predators. These chemicals are carried over into the adult butterfly, so the protection is lifelong.

Of the more than two dozen species of native Florida milkweeds, most are herbaceous perennials that become dormant during the winter months. The rest. are vines. Some, such as various members of the genus Matelea, are exceedingly rare. Certain Asclepias species also are listed as endangered or threatened. Only one of these, A. curtissii, is still found in Pinellas, in well-drained uplands. Most species have specific habitat needs, and occur in localized populations. In using these milkweeds in the home landscape, you will need to match their needs closely. Below is a brief description of some of the most interesting species for possible use in our area.

Butterfly milkweed (A. tuberosa) is the most recognized and widely available species in the genus. Its umbels of bright orange flowers provide a good show of color as well as a valuable nectar source. It does not, however, produce a milky sap and is not commonly used by milkweed butterflies as a larval food plant. Usually multi-stemmed and about 12 to 18 inches in height, this plant is native to upland sandy habitats throughout Florida.

Purple milkweed (A. humistrata), also called sandhill milkweed) is characterized by large broad blue-green leaves with purplish veins. Although this is a robust plant, the two-foot stems generally lie on the ground. A mature plant forms a rather large clump. The cream-color flowers occur early in the spring and last for just a few weeks. Purple milkweed is native to well-drained sands and will rot quickly if drainage is not good.

Velvet-leaf milkweed (A. verticillata) is not especially showy and may not attract much attention from anyone not interested in butterflies. It is a lanky, single-stemmed species, often reaching two feet in height, with rounded, wooly leaves. The large flowers are greenish-white in color and occur in clusters around the stem. Like the above two, it also needs well-drained soils.

Long-leaf milkweed (A. longifolia) is a somewhat rare, few-stemmed species that rarely exceeds 12 inches in height. As its name implies, the leaves are long and narrow. The flowers are white and attractive, although not especially showy. Longleaf milkweed occurs in seasonally flooded flatwoods and likely is adaptable to many typical home landscape settings.

Few-flowered milkweed (A. lanceolata) is a very lanky single-stemmed species that may reach 3 to 4 feet in height. The small umbels of bright orange flowers bloom in summer. This is a wetland plant that occurs in seasonally flooded areas throughout Florida. Few-flowered milkweed produces very little foliage, but its bright blooms would make an attractive addition to a seasonally wet area.

Swamp milkweed (A. incarnata) is another resident of seasonally wet areas. This is a robust single-stemmed plant that may reach three feet tall. Its broad umbels of soft pink flowers are very showy in the summer. Few milkweeds attract nectaring butterflies better. Swamp milkweed is seasonally adaptable, but it does best here when it is kept in areas that stay wet during the summer months. This plant should be widely grown, but I know no Florida nursery that offers it.

Published on  07.31.2012