Asclepias tuberosa

Three subspecies of Asclepias tuberosa are recognized by Kartesz (floristic synthesis, 1999): subsp. interior, comprising populations roughly from the Appalachian area and westwards; subsp. tuberosa, comprising populations east of the Plains states; and subsp. rolfsii, comprising populations in Florida and in adjoining states (Kartesz, 1999; USDA-NRCS 1999). The subspecific divisions are based mainly upon leaf shape, and are loosely separated along introgressive boundaries (Cronquist et al. 1984).

Although this species remains very common in parts of its range, it appears to be in severe decline in others. Habitat destruction and manipulation has caused a range wide decline of this species. The general center of this species distribution (the eastern tallgrass prairie states) has been almost entirely converted to agricultural and urban uses. Fragmentation of remaining habitat, contamination of the gene pool, and wild harvesting present ongoing threats to this species. Nevertheless, it is still quite common in semi-natural settings such as roadsides and old fields.

A. tuberosa occurs in southeastern Canada, south through all states in the eastern half of the continental United States (except North Dakota), and southwestwards into Utah, California, and northern Mexico (USDA-NRCS 1999, Cronquist et al. 1984). This species is known from only one site in Maine, where it has since been extirpated (Maine Natural Areas Program).

Many thousands of populations are extant rangewide. Nebraska: common, but rarer than formerly due to land use changes; Kansas: probably thousands of populations, scattered in tallgrass and mixed-grass prairies across the eastern two-thirds of the state; Missouri: common; Arkansas: reported from almost every county; Georgia: very common; Mississippi: occurs commonly over a large area, 47 counties; New York: probably about 100 populations; Vermont: known only from several collections from the late 1800's and early 1900's, all made within two counties; Indiana: common, occurs throughout the state, especially in the northern portion; Illinois: very common, frequently encountered in prairie areas, especially in sand prairies; Michigan: relatively common throughout southern Lower Michigan, ranges through northern Lower Michigan, frequent in prairies, old fields, prairie remnants, roadsides, along railroads, etc.; Ontario: about 100 populations; Kentucky: infrequent but not tracked; Texas: common, not tracked; New Hampshire: listed endangered, known only from seven historical occurrences (Natural Heritage Programs).

There is some collecting in Missouri from roadsides for use in home landscaping, but no medicinal collecting (Tim Smith pers. comm.). It may be collected for use in prairie restoration, and for ornamental use (Mike Penskar pers. comm.). It is used ornamentally in gardens (Niering 1979). At least one wild population in Illinois has been damaged by direct collecting of whole plants. In other cases, where cultivated varieties don't represent local genotypes, there is a threat that genetic contamination of the wild populations is occurring, as the wild and cultivated populations intermix.

An individual familiar with the herbal medicinal commercial markets in the U.S. estimates that this plant receives minor to moderate usage which is not increasing, and states that the plant is not cultivated. It is the roots that are collected (McGuffin pers. comm.).

A. tuberosa may be poisonous to livestock (Great Plains Flora Association 1986). Though there are no known reports to this effect, it is possible that farmers andranchers try to diminish this species when it occurs on their land.

Many of the habitats reported for A. tuberosa are open or semi-open communities (prairies, fields, open woodlands, dry woods, savannas, barrens, shrublands, etc.). In recent years there has been an increasing awareness of the role of fires in maintaining such communities, and in the increasingly poor condition of these communities after decades of lowered fire frequency. In the Great Lakes region, for example, many oak-dominated barrens on sandy soils have reverted to structurally forested or thickety habitats in the absence of fire, and this is detrimental to A. tuberosa. Furthermore, many native prairie relicts within the range of A. tuberosa are legally protected but are suffering from lack of adequate management attention. In such cases the survival of A. tuberosa is probably not certain (though some regional floras describe A. tuberosa as somewhat weedy, and thus possibly tolerant of natural community deterioration, others do not (Swink and Wilhelm 1994)).

In Nebraska, this species is threatened by cattle grazing, annual midsummer haying, pesticide application, plowing of prairie, and exotic plant invasions (Gerry Steinauer pers. comm.). In Ontario, it is reportedly threatened by loss of prairie and savanna habitats due to lack of fire, invasions by exotics, overgrazing by deer, and conversion of habitat for agricultural uses (Mike Oldham pers. comm.). The primary threats in Kansas are from urban and agricultural developments, and overgrazing (Craig Freeman pers. comm.).

This species is included on the United Plant Savers "To Watch List" (United Plant Savers 2000).