Florida's Butterfly Milkweed Varieties: There's a good chance your nursery is selling a non-native variety.

At least six varieties of butterfly milkweed (Asclepias tuberosa) occur in the coastal plain of the southeastern United States, all of which can be found in Florida. Three of these varieties have been described, and three have not. Despite this diversity, typically only one variety is commonly grown in the nursery industry and is often derived from populations not native and adapted to the outer coastal plain. To assist the public in field identification or in choosing the correct variety for restoration or gardening, here is a quick summary of the varieties commonly-encountered in the southeast. Big takeaway from this article: unless you live in several specific areas, the variety of milkweed that a majority of sites should have for landscaping or habitat restoration is Asclepias tuberosa var. rolfsii – Rolf’s milkweed.

Seedling Morphological Comparison

NOTE: 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, if they are the correct variety for your property or project, and if they are likely to survive. 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 Three Described Varieties Butterfly Milkweed of the Southeast’s Outer Coastal Plain:

1) Asclepias tuberosa var. rolfsii – Rolf's milkweed:

Three varieties of butterfly milkweed have been officially described in Florida, but the other three varieties have not been assessed thoroughly to determine if varietal subspecies classification is warranted.

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 table 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 crispate (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.                             

variety rolfsii presenting their hastate (lobed) leaf bases

2) Asclepias tuberosa var. tuberosa – butterflyweed:

variety tuberosa persisting in a cemetery

                                                

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.

variety tuberosa showing their cuneate (unlobed) leaf bases

3) Asclepias tuberosa var. 2 - the scrub butterflyweed: 

variety 2 persisting along roadside 

 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 tuberosa var. rolfsii AND 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.

 

variety 2 presenting proportionately shorter, occasionally-notched leaves 

Other Varieties:

There are three other varieties in the deep south that are not officially described:

4) Everglades Butterflyweed - a rolfsii lookalike that can be 36' tall, and grow in poorly-drained flatwoods with seasonal flooding and sheetflow. This variety is typically found from Lake Okeechobee and south, with significant populations in southwest Florida.

Everglades ecotype in flooded wet prairie margin with flatwoods

5) Red Hills Butterflyweed - likely a product of introgression between var. rolfsii and var. tuberosa, these plants present attributes of both varieties. Such plants typically have cuneate leaf bases with crispate leaf margins and periodic, reduced lobes on the leaf bases. As entire populations of these plants are observed and are reproducing at the regional scale, these populations are established beyond being classified as a localized, hybrid population. Such populations are found throughout the Tallahassee Hills, Tifton Uplands, the Dougherty Plain, and the Southern Pine Plains and Hills. These populations typically occur at the friction zones (along geological-ecoregion gradients) between var. tuberosa populations to the north and populations of variety rolfsii to the south (below escarpments). 

Red Hills ecotype with cuneate and subcordate leaf bases, and crispate margins

6) Altamaha Butterflyweed -  this ecotype may be relictual where it persists. Populations were initially observed in southeastern Georgia growing within Altamaha grit formations, and have since been found in several other locations in the central Florida Panhandle. It is thought that there may be undocumented populations elsewhere between these known populations. This variety grows in very arid, xeric, downright-hostile conditions. In both the Georgia and Florida populations, this variety grows on either bare rock and/or large-angled-silicate sands that typically exclude all other milkweeds from recruitment. In the Georgia populations, this tuberosa ecotype is frequently sympatric with Asclepias obovata. A defining feature of this ecotype are the noticeably linear or acicular leaves, which are typically very skinny when compared to other ecotypes.

Altamaha ecotype in Fountain, Florida

Altamaha ecotype in Kite, Georgia

Overall Horticultural Facts, Implications and Generalizations:

• With the exception of a few areas along Florida's border with Alabama or Georgia on rich upland soils, Asclepias tuberosa var. rolfsii is the variety that nurseries must sell in-order to be providing a native ecotype to the public throughout virtually all of Florida. The Milkweed Foundation has only seen native ecotype sold one time, at one nursery, with all other nursery stock being from Asclepias tuberosa var tuberosa stock from regions far away from the coastal plain..
• All varieties have cuneate leaf bases in their first year of life, but widths and lengths are demonstrably different.
• 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 very likely not native to your region, climate, or habitats, and will not perform well!