milkweed_mapper's Journal

Native milkweeds and their habitats have undergone great declines due to habitat loss from development and fire-suppression, and populations under powerlines or roadsides comprise a bulk of remaining milkweed resources in many places. Roadside mismanagement with overmowing and herbicide utilization and roadside construction are drastically-impacting these remaining populations. Aggressive and immediate actions are necessary to prevent a majority of Florida’s milkweeds from vanishing.

Between 2013 and 2023, The Milkweed Foundation conducted extensive surveys across Florida and surrounding states. 23 milkweed and 6 milkweed vine species were documented and mapped. Milkweed populations were assessed (among other considerations) for the following:

• Phenologies – e.g., when milkweed species flower, fruit, etc.
• Status – e.g., are populations secure, increasing, declining, etc.
• Distribution patterns
• Recruitment (seedling germination)
• Current threats
• Soil characteristics
• Associated and/or sympatric species
• Monarch butterfly utilization rates

One of the more concerning facts arising from our study relates to the current distributions of milkweeds across Florida and surrounding coastal plain states.

The vast majority of milkweed population strongholds are confined to roads or powerline easements, with a minority of strongholds being found in cattle pastures, pine plantations, and cemeteries. At the landscape scale, roadside and powerline populations are the only remaining native milkweed population in many districts; this fact holds true on both public and private lands. A great example to demonstrate our findings can be found by reviewing survey data for three of Florida’s most important native milkweed species:

Population Geography Statistics for Three Important Milkweeds in Florida

Of the 616 populations in the table above, only 72 (11.69%) of the populations were detected within intact natural communities. In many places, roadside populations are linear, and surrounded by roads or development activities.

To review baseline data used to build this table, go here.

Asclepias humistrata and Asclepias tuberosa are upland species dependent upon fire disturbance and a healthy native plant community. In much of the their ranges in Florida, populations end at the “mow line” along the backslope of road right-of-ways (ROWs). Even where native plant communities persist adjacent to the ROWs, this populations only persist in the ROWs due to a lack of consistent fire management in the adjacent native plant communities.

Asclepias perennis typically occurs in forested wetlands disturbed by water flow, and has incurred less anthropogenic impacts than the aforementioned upland species. Despite this, many ROW populations of Asclepias perennis are also roadside-only because of modifications to the hydrology of surrounding wetlands.

The resulting phenomenon are "linear distributions" of milkweeds along the linear facilities of virtually every region in the state. Here are what these roadside bottlenecks look like:

Roadside-Only Population of Asclepias lanceolata

Roadside-Only Population of Asclepias perennis

Roadside Bottleneck of Asclepias viridis

Roadside-Only Population of Asclepias humistrata

Typical Roadside Milkweed Bottleneck along "Mow Line" Backslope of ROW

In the time since our survey efforts began in 2013, more than half of the populations that The Milkweed Foundation has mapped and monitored have been impacted or eliminated by road-widening projects, excessive mowing, or herbicide applications!

7-19-2023 - Levy County, Florida: Mass Herbicide Kill of Roadside Asclepias perennis

Generalization: Native milkweeds and their habitats have undergone great declines due to habitat loss from development and fire-suppression, and populations under powerlines or roadsides comprise a bulk of remaining milkweed resources in many places. Roadside mismanagement and herbicide utilization are drastically-impacting these remaining populations time. Aggressive and immediate actions are necessary to prevent a majority of Florida’s milkweeds from vanishing.

There is a common misconception that all native milkweeds in the southeast are dormant during the winter months.

The point of this entry is to inform the public that current discussions and debates regarding “artificial winter populations” of monarch butterflies in Florida and the southeastern United States are not appealing to an important fact:

Large, wild, evergreen populations of native milkweed are available to monarch butterflies throughout the deep south. The native species of milkweed at the center of this exciting information is aquatic milkweed - Asclepias perennis.

A large, roadside population of aquatic milkweed in Taylor County, Florida
On on December 28th, 2014, Scott Davis, a park ranger at St. Marks National Wildlife Refuge, was leaving for the day when they noticed a plant flowering along the roadside. Upon further investigation, it was determined to be a flowering aquatic milkweed (Asclepias perennis).

As bewildering as it was to observe a native milkweed flowering in North Florida in December, it was more intriguing to the ranger to observe monarch butterfly caterpillars were actively feeding on the milkweed!

December 28th, 2014 - Monarchs and Native Milkweeds are Observed as Winter Active
The ranger reported the winter milkweed observation to entomologists studying the annual monarch migration and was surprised to learn that none of them were aware that a native milkweed, in its native habitat, was actively growing (and providing larval food) in the winter dormant season.

The park ranger’s observations were considered by various researchers and incorporated into publications.

Ø Aquatic Milkweed Surveys lead to BIG Discoveries

Prompted by the discovery of aquatic milkweed’s evergreen nature, the Milkweed Foundation organized largescale surveys for aquatic milkweed. Populations of aquatic milkweed were documented and investigated across Florida, ranging from temperature zone 8a in the Florida Panhandle to temperature zone 10b in southwest Florida, at the southern boundary of aquatic milkweed’s distribution.

Milkweed Foundation - Aquatic Milkweed Survey Points
Key takeaways from our aquatic milkweed survey results are as follows:
o Aquatic milkweed is a year-round, evergreen milkweed across its entire range in the State of Florida and surrounding coastal plain states.

o Monarch butterflies were documented utilizing aquatic milkweed as a larval host species 12 months of the year in Florida, statewide.

o Aquatic milkweed is currently providing large biomasses of material for monarch butterflies due to the large populations present within its range in Florida and surrounding states.

o Winter observations of monarch butterflies utilizing aquatic milkweed demonstrate that monarch populations are not inherently artificial or associated with plantings or colonies of non-native milkweeds.

Further Support for the Presence of Winter Milkweeds and Indigenous Winter Monarchs

The Milkweed Foundation has spent the last eight years surveying milkweeds across the deep south, notably in Florida. A full survey of native milkweed phenologies - i.e., their growing and flowering periods - has been recorded.

Milkweed Foundation - Florida Native Milkweed Survey Points
Key takeaways from our multi-species milkweed survey results are as follows:

South of approximately Orlando, Florida, the following milkweed species have consistently demonstrated dormant season growing phenologies:

o - Asclepias tuberosa var. rolfsii

o - Asclepias lanceolata

o - Asclepias longifolia

o - Asclepias perennis

o - Asclepias tomentosa

o - Asclepias verticillata, specifically the wet prairie ecotype only known from Peninsular Florida

o - Asclepias viridis

North of Orlando, Florida, the only native milkweed that is consistently phenologically-active all winter is aquatic milkweed. Traveling north from central Florida, populations of aquatic milkweed become larger at the landscape scale, and their distributions more prevalent.

Florida's Winter Milkweeds

Reasons for Aquatic Milkweed's Impacts on Monarch Butterfly Populations of the Southeast:

As has been consistently observed since the beginnings of our survey endeavors, Aquatic milkweed does not senesce (defoliate) for the winter in Temperature Zones 8-10, and minimally (in cold winters) for Temperature Zone 7B+. We have not attempted winter observational data for this species north of 7B. Other native milkweed species in the southeastern U.S., with the exception of milkweed ecotypes in Central and Southern Florida, senesce in the winter months.

Aquatic milkweed is tough! Populations are subject to freezing conditions nearly-annually throughout much of their range in the deep south. Winter frost and frozen-over surface waters do not defoliate these plants. When the ice thaws or melts, the evergreen nature of aquatic milkweed is unscathed by the cold conditions. Hydric soils figure into this phenomenon, as plants cultivated in upland garden conditions will experience leaf dehydrating (leaf shriveling) similar to what occurs with other familiar winter evergreen species, such as Catawba rhododendron.

Photo-documented occurrences of monarch larvae (at multiple instars) and of females ovipositing eggs have been documented on aquatic milkweed every month of the year, statewide across Florida. Many of these observations have occurred in very remote locations, far away from human settlements; and thus, no urban heat zone or vector for artificial populations is anywhere nearby.

February 10th, 2023 - Surveys Detect Monarchs and Aquatic Milkweeds Statewide

Aside from being evergreen, aquatic milkweed is a preferred milkweed by monarchs:

Butterfly milkweed (Asclepias tuberosa) and sandhill milkweed (Asclepias humistrata) are important milkweeds to comparatively assess in the southeast when attempting to determine the importance of aquatic milkweed to monarch butterflies. Butterfly milkweed is considered one of the most widespread and secure milkweed species in North America, and sandhill milkweed is considered one of the most important larval host milkweeds for monarchs in the southeastern United States.

A largescale species assessment for all three species was conducted over the last ten years, and the results are very interesting!

Monarch Utilization Statistics for Three Important Milkweeds in Florida

The results of our survey are generalized in the table above. To review the large dataset behind this table, go to our Data page, or click here.

In a nutshell, monarchs utilize aquatic milkweed all year, and they love it! Our survey data suggests that monarchs show preference for aquatic milkweed, with 76% (48 discrete populations) having monarchs being documented at least once. Out of 248 wild populations of butterfly milkweed, monarchs were only documented at twice!

Butterfly milkweed and sandhill milkweed (like most milkweed species in Florida) are sharply declining and mostly located along roads or powerline easements. Although also declining and frequently roadside-only, aquatic milkweed maintains larger population numbers and distributions due to its forested wetland habitat.

Recently, roadside aquatic milkweed populations have begun to vanish due to the increase in herbicide utilization by agencies and linear facilities companies. The issue must be addressed soon!

The Best Place in Florida to Study Aquatic Milkweed and Winter Utilization by Monarchs:

Although aquatic milkweed populations can be found easily across its range, several hot spots for observing winter behaviors of aquatic milkweeds and monarch butterflies have been identified. Florida’s Big Bend coastal district is one-such region. The Big Bend is a phytogeographical interface between the Florida Panhandle and Peninsular Florida, and holds very high densities of aquatic milkweed. We refer to this region at Florida’s “monarch belt” as it is a friction-interaction zone between non-migratory and migratory monarch butterflies; and, the region holds Florida’s most voluminous populations of native milkweeds.

Monarchs travel through the Big Bend during their spring and fall migrations. Beyond this point, it is unclear where (all) the monarchs go. In the autumn migration, we do not know how much of the monarch population disperses west along the gulf coast toward their hibernaculums in Mexico, or how much of the population disperses south into peninsular Florida. The Big Bend is one-such area where large populations of evergreen aquatic milkweed provide resources and incentives for monarchs to hang-out, and exit reproductive diapause.

On the north end of this "milkweed belt", the monarch populations are presumed to be migratory, but on the south end, (from Citrus County and south) the butterflies are presumed non-migratory.

Are monarchs following this belt of milkweed down into the peninsula, much as they form non-migratory populations in cities? Is the Big Bend a geographical interface at which the migratory and non-migratory populations are interacting?

One thing is for sure - Florida is providing monarchs with year-round resource potential. If the climate were to transition into a long-term warming trend, it would follow that there would be increasing numbers of monarchs documented overwintering in the region. Please reference our other pages on Asclepias perennis for more detail on the facts we have documented regarding the species.

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!