Butterfly milkweed (Asclepias tuberosa) is complicated! In fact, the species forms a complex of several different varieties in the southeast. To assist the public in field identification, or in choosing the correct variety for restoration or gardening, here is a quick summary of the 3 varieties commonly-encountered in the southeast. **It is VERY important to recognize which variety you are considering when preparing to purchase plants or seeds, as particular varieties can tell you a great deal about where the plants have come from, and if they are the correct variety for your region or habitat. Despite the seemingly-slight differences in morphologies, these varieties occupy distinct natural communities and soils, to which they are uniquely adapted. Please reference the most-recent version of Weakley’s Flora for full morphological descriptions of these varieties. The 3-Primary Varieties: 1) Asclepias tuberosa var. rolfsii - Rolf’s milkweed: Var. rolfsii is found throughout much of Florida and spans the outer coastal plain from southern Alabama to the eastern portions of the Carolinas and southern Virginia. The fall line sandhills of Georgia and the Carolinas, the Cody escarpment sandhills of the Florida Panhandle, and the Trail Ridge and Lake Wales Ridge of peninsular Florida are premiere locations to view this variety. In the majority of its range, Rolf's milkweed occupies sandhills and occasionally clayhills (high pine natural communities). In peninsular Florida, this variety is found in sandhills, but also occurs in yellow and white sand scrubs, scrubby flatwoods, mesic flatwoods, wet flatwoods in the Everglades region, and limestone pine rocklands in deep southeastern Florida. Generally, rolfsii likes fire-maintained, xeric uplands, with the exception being the south Florida ecotypes that grow in high water tables flatwoods with seasonal sheet flow. Among other morphological distinctions, a primary trait useful for quick field identification of rolfsii is to inspect the leaf bases. Var. rolfsii will have hastate or cordate leaf bases that are usually crenate (wavy). Leaves tend to be 3 times longer than they are wide. There is a great deal of variability in variety rolfsii. For example, in the Alapaha grit district of southeastern Georgia, variety rolfsii has notoriously skinny leaves, where the leaves can be 10 times longer than they are wide! Please view attached photographs (iNat observations) to compare with other varieties. 2) Asclepias tuberosa var. 2 - the scrub butterflyweed: This is the rarest of the three varieties in the lower southeast. It is almost exclusively found in peninsular sand ridges, with the largest populations occurring along the Lake Wales Ridge. Unless you frequent low, ancient scrubs, you may not encounter this variety. Milkweed Foundation Surveys have shown that variety 2 occurs in peninsular scrubs but is often found in separate microhabitats from Asclepias curtissii. Variety 2 tends to grow in areas with slightly higher moisture, lower elevation, or transitions into yellow sands from white sands. For any level of experience with the A. tuberosa complex, this variety looks WEIRD. The leaves are noticeably broad and are typically only twice as long as they are wide. The ends of the leaves are broad and round, and sometimes have a noticeable notch. Leaf bases are hastate or subcordate, but not as dramatically as is seen in variety rolfsii. 3) Asclepias tuberosa var. tuberosa – butterflyweed: Spanning a beltway across the upper coastal plain of the Carolinas, Georgia, Alabama and in a few regions of far-north Florida, A. tuberosa var. tuberosa occurs, and introgresses with Asclepias tuberosa var. rolfsii. Var. tuberosa inhabits upland mixed-woodland, high pine, clay hill, post oak savanna, and occasionally sandhill; in Florida, it is generally only found in counties that are adjacent to the state border. Generally, variety tuberosa likes fire-maintained, mesic uplands. It is common to find populations of introgressed individuals between tuberosa and rolfsii populations. This often occurs where geological platforms transition from interior plains of red loams and clays into escarpment sandhills. The western panhandle is the best place to see rolfsii and tuberosa populations with introgressed hybrid populations between them. Among other morphological distinctions, a primary trait useful for quick field identification is to inspect the leaf bases. Variety tuberosa will have leaf bases that are rounded, cuneate (tapering), or slightly lobed. Its leaf margins are typically smooth, and not wavy. Variety tuberosa will NEVER present large, lobed leaf bases, which the other two varieties present. This makes separating this variety easy.
Horticultural Facts and Implications:
All varieties have cuneate leaf bases in their first year of life.
Virtually all tuberosa sold in the deep south is not variety rolfsii or variety 2.
Variety tuberosa or other tuberosa varieties from far away are usually marketed as native milkweed in the deep south.
If you live in Florida or the outer coastal plain, and your local nursery is selling varieties of tuberosa that do not have lobed, hastate, or subcordate leaf bases, it is not native to your region, climate, or habitats, and will not perform well!