Mead's Milkweed (Asclepias meadii Torrey ex A. Gray)
This document is intended to assist land managers in protecting and enhancing populations of the federally threatened plant, Mead's milkweed. Mead's milkweed is a late-successional species that requires high-quality prairies or glades. Populations have markedly declined on some of our public prairies within the last decade. Although single-species management is not advocated, there are a number of practices that can be followed that will benefit Mead's milkweed without compromising management of the natural communities in which it occurs. Our knowledge of optimum conditions for the growth and spread of Mead's milkweed is not complete. But researchers have discovered some interesting genetic and life history characteristics that can help direct our actions. This guidesheet will put the facts gleaned from such research where they can do the most good, in the hands of land managers.
IDENTIFICATION
Mead's milkweed is a herbaceous perennial with an erect stem growing 1 to 2 1/2 feet tall. It has a smooth stem with milky sap; 2 to 6 pairs of opposite, tapering leaves; and a nodding inflorescence (Figure 1). It is one of a dozen species of milkweeds (genus Asclepias) that occur in Missouri glades and prairies, so some familiarity with the group is necessary in order to make an accurate identification. It most closely resembles Asclepias viridiflora, from which it can be distinguished by its broader leaf bases and its single flower cluster located at the top of the stem. Asclepias amplexicaulis is somewhat similar but has broader, less tapering leaves with bluntly rounded apices. Non-flowering Mead's milkweed plants might also be confused with non-flowering dogbane (Apocynum spp.), which occurs in similar habitat and also has milky sap.
Mead's milkweed flowers from late May to mid-June. Flowers occur in one nodding cluster at the top of the stem. The cluster (an umbel) can have from 5 to 14 individual flowers, which are yellow-green or greenish cream and may be tinged with purple. Individual flowers have five tubular hood-shaped structures (nectaries) with a slender "horn" extending from each one.
(1) Mead's milkweed in flower (2) Mead's milkweed in fruit.
Green pods develop following flowering and usually mature by mid-September. The slender, pointed pods can grow to 1 1/2 to 4 inches in length. Mature pods dry and split down the side to release seeds with a parachute-like cluster of attached hairs, typical of milkweeds. Each pod produces approximately sixty seeds (Betz 1989). Fruiting appears to occur rarely at most sites (Betz 1989, Betz & Lamp 1990).
A single plant of Mead's milkweed may consist of multiple stems of varying sizes. One to several larger stems, either flowering or sterile, may be surrounded by additional, much smaller, sterile stems. Stems arise from the plant's rootstock or from a spreading rhizome and may be separated by a meter or more from each other. The shorter, thinner stems usually do not flower and are so reduced in height and leaf width that they may not be recognized as Mead's milkweed. These stems closely resemble small plants of dogbane (Apocynum spp.). They may often be found by meticulously searching the area around a larger stem.
For a key to separate Mead's milkweed from related species, see:
Steyermark, J.A. 1963. Flora of Missouri. Iowa State Press. Ames, Iowa. 1728 pp.
POLLINATION
Mead's milkweed plants are self-incompatible, i.e. a plant cannot be pollinated by pollen from one of its own flowers. It may also be incapable of cross-pollination from the flowers of another Mead's milkweed if the two plants are closely related (Bowles et al. 1995). According to Betz (1994), the natural pollinators are digger bees (Anthophora spp.) and bumblebees (Bombus spp.), with the latter probably being the less efficient. The exotic honeybee (Apis mellifera) also visits the flowers but may not be capable of effecting pollination (Betz et al. 1994).
HABITAT and DISTRIBUTION
In Missouri, Mead's milkweed is found on dry-mesic and mesic prairies and on igneous glades. Known prairie populations occur in the Grand River Section of the Glaciated Plains Natural Division (Harrison County), the Springfield Plateau Section of the Ozarks Natural Division (parts of 6 counties) and in the Osage Plains Natural Division (parts of 9 counties). Igneous glades containing the species are within the St. Francois Mountain Section of the Ozark Natural Division (Iron & Reynolds counties). Igneous glade sites are all on public lands. Prairie sites include public prairies as well as private hay meadowprairies.
There are undoubtedly additional sites for Mead's milkweed in Missouri that have not yet been discovered or reported. Remnant prairie habitats along roadsides, railroad rights-of-way and within old cemetery boundaries can also provide suitable habitat. Any new sightings of Mead's milkweed should be reported to the Natural Heritage database, Natural History Division, Missouri Department of Conservation.
The following Missouri public lands are known to contain populations of Mead's milkweed. EORANK refers to the size, health, and threats to a particular site. A-ranked sites in general being larger, healthier and better protected than D-ranked sites.
| COUNTY | SITE NAME | EORANK |
|---|---|---|
| Barton | Catlin Prairie Conservation Area | D |
| Barton | Prairie State Park | C |
| Benton | Hi Lonesome Prairie C.A. | C |
| Cedar | Mo-Ko Prairie | D |
| Dade | Niawathe Prairie | A |
| Harrison | Wayne Helton Memorial Wildlife Area | D |
| Henry | Truman Reservoir lands | C |
| Iron | Bell Mountain Wilderness - USFS | C |
| Iron | Taum Sauk Mountain State Park | B |
| Pettis | Friendly Prairie C.A. | D |
| Pettis | Grandfather Prairie C.A. | D |
| Pettis | Paintbrush Prairie C.A. | C |
| Polk | LaPetite Gemme Prairie | D |
| Reynolds | Proffit Mountain C.A. | D |
| St. Clair | Taberville Prairie C.A. | D |
| St. Clair | Wah-Kon-Tah Prairie | C |
| Vernon | Gay Feather Prairie C.A. | C |
| Vernon | Little Osage Prairie | C |
| Vernon | Osage Prairie C.A. | C |
MANAGEMENT EFFECTS
A number of management practices have been used on lands containing Mead's milkweed populations. These include: haying, resting (no active management), prescribed burning, and grazing. The effects of these management practices on this milkweed are not completely understood. But research into the life history and population genetics of the species has begun to shed some light on appropriate management techniques. Preliminary findings are summarized below:
HAYING
Haying of prairies can have direct and indirect effects on Mead'smilkweed. The most obvious direct effect is that haying during the growing season (April 1 to mid-September) will remove growing stems and, if present, the flowers or immature fruits. This eliminates the opportunity for sexual recombination and for seed production that year.
Many years of annual haying prior to seed maturity may lead to an increase in vegetative spread by rhizomes. So more stems may be produced from each plant, but fewer stems will have flowers and stem size and number of flowers per umbel diminish. Evidence from annually hayed prairies versus frequently burned prairies indicates that genetic diversity within the haymeadow populations may be reduced as individuals less successful at clonal spread die out and are not replaced by seed production (Bowles et al. 1995).
The effects of haying after seed maturity are less well known because few prairies with that kind of management history are available to study. Late season haying tends to cause forbs to proliferate. The effects of competition from grasses or other forbs on Mead's milkweed are not known. The species was first found at Helton Prairie Natural Area (Harrison Co.) after two successive years of fall disturbances, haying in 1992, then burning in 1993. It is unlikely that flowering Mead's plants would have been missed during previous plant surveys of this small, high-quality prairie.
RESTING
Resting of prairies, i.e. not haying, burning, or grazing, is commonly used on many areas managed by the Missouri Department of Conservation. The effects on Mead's milkweed of resting a prairie unit for one year may be rather minor. Successive years of resting would of course allow greater establishment of woody species as well as stifling forb growth through litter accumulation.
If a prairie is managed by grazing or haying during Mead's growing season, then a resting period may be the only chance for the plant to produce a seed crop. Betz (1989) has noted, however, that a reduction in viable seed production was found in plants that were mowed the previous season, possibly due to a lowered level of food reserves. If haying is conducted after the milkweed has dispersed its seeds, then the resting period may not be preferable to annual haying. Lack of manpower and suitable conditions for burning or haying all management units every year assures that resting will continue to be used in management of many sites. Resting the same unit for successive years should be avoided, although it would be preferable to mowing, grazing, or burning during the Mead's growing season.
PRESCRIBED FIRE
The use of prescribed fire seems to stimulate flowering in Mead's milkweed populations and thus increases the chances for pollination and seed production, which can maintain genetic diversity. Burns conducted during the milkweed's dormant season, between late September and April 1, will avoid burning actively growing milkweeds. The first documentation of Mead's at a couple of Missouri sites occurred following dormant season burns.
Mead's milkweed plants in burned prairies are typically more robust than in hayed prairies, both in overall size of the plant as well as in the number of flowers per umbel (Bowles et al. 1996). Bowles et al. found that, with few exceptions, the density of Mead's plants on burned prairies is lower than on summer-hayed prairies, where continuous cutting of stems may promote the proliferation of clonal shoots. But the less dense, burned populations contain a higher percentage of flowering plants and higher genetic diversity. One of the larger and more genetically diverse, sexually reproducing Mead's populations is found at Rockefeller Prairie, Kansas (Bowles et al. 1996). That site has been burned every two to five years since the 1950's. Prior to 1950, the prairie had been hayed annually.
GRAZING
Little information exists on the effects of grazing on Mead's milkweed. The species has occurred on some annually grazed prairies according to Toney (1986). The chance of damage from grazing increases on smaller prairie tracts where plants are more likely to be grazed, trampled, or crushed by bedding livestock. This milkweed is reportedly more palatable to cattle than other milkweeds (Chaplin 1986). Grazing is less frequently used on Missouri's publicly managed prairies than either haying or prescribed burning.
MANAGEMENT RECOMMENDATIONS
Based on information available today, the following recommendations are made for prairie management units containing Mead's milkweed populations.
- Delay haying until after Mead's milkweed has dispersed seeds, i.e. mid-September or later.
- Use prescribed burning between late September and April 1 to stimulate sexual reproduction in Mead's. Conduct some prescribed burns in late September or October to stimulate forbs. Burn management units at least once every five years.
- Be sure that land managers and permitee hayers are not attempting to destroy colonies of the bees that pollinate Mead's milkweeds. Colonial bees can harass hayers who sometimes resort to pouring gasoline down holes to kill them. Later haying, as recommended, would lessen the potential for this occurring.
- Do not introduce grazing to Mead's sites that are not currently grazed. On currently grazed sites, do not increase grazing pressure by adding head or reducing the size of the grazing unit.
References Cited
- Betz, R.F. 1989. Ecology of Mead's milkweed (Asclepias meadii Torrey). Pages 187-191 in Proceedings of the Eleventh North American Prairie Conference.T.B. Bragg & J. Stubbendieck, eds. University of Nebraska at Lincoln.
- Betz, R.F. & H.F. Lamp. 1990. Flower, pod, and seed production in eighteen species of milkweeds (Asclepias). Pages 25-30 in Proceedings of the Twelfth North American Prairie Conference. D.D. Smith & C.A. Jacobs, eds. Cedar Falls, Iowa.
- Betz, R.F.,R.D. Struven, J.E. Wall & F.B. Heitler. 1994. Insect pollinators of 12 milkweed (Asclepias)species. Pages 45-60 in Proceedings of the Thirteenth North American Prairie Conference. R.G. Wickett, P.D. Lewis, A. Woodliffe & P. Pratt, eds. Department of Parks & Recreation, Windson, Ontario, Canada.
- Bowles, M.L., B. Schaal, D. Hayworth, K. Williamson, D. Tecic & D. Nickrent. 1996. Management effects on population structure of Mead's milkweed, a federal threatened prairie species. Abstract - Ninth Missouri Forest, Fish, & Wildlife Conference. Osage Beach, MO.
- Bowles, M.L., D.Tecic, D. Nickrent, B. Schaal, D. Hayworth & W. Kerry. 1995. Recovery and restoration implications of DNA and allozyme variation in Mead's milkweed. Unpublished report to the U.S. Fish & Wildlife Service. The Morton Arboretum, Lisle, IL.
- Chaplin, Steve. 1986. Missouri Department of Conservation memo: Mike Sweet to Thom, Wilson, and Morgan. Unpublished memorandum. Missouri Department of Conservation.
- Toney, Thomas E. 1986. Missouri Department of Conservation memo to Don Kurz. Unpublished correspondence. Missouri Department of Conservation.
Copyright 1996 Missouri Conservation Commission
Missouri Department of Conservation2901 W. Truman Blvd.
P.O. Box 180
Jefferson City, MO 6510
