Rare Species Guide

  Basis for Listing

Many special concern plant species are so listed because they occur in an unusual type of habitat or because they occur here at the very edge of their range. The case of Phlox maculata (wild sweetwilliam) is somewhat different; it was relatively widespread and perhaps even common in portions of Minnesota at the time of settlement. In fact, its grassland habitat was abundant in several southeastern counties (Eastern Broadleaf Forest Province). Regrettably, its habitat has since declined to perhaps one percent of its original extent (Minnesota's Remaining Prairie), with a concomitant loss of P. maculata. Most of the habitat was converted to agricultural purposes such as crop production and livestock grazing. Further losses can be attributed to the expansion of urban areas, commercial developments, and road building. Further survey work is needed to clarify this species’ distribution in wet meadow habitats, but given the small number of known populations and the well-documented loss of its prairie habitat, it was listed as a special concern species in 2013.

  Description

Stems of P. maculata are erect, 30-80 cm (12-23 in.) tall, and usually red-spotted. The leaves are 5-12 cm (2-5 in.) long, firm, shiny and lanceolate in outline. The flowers are in terminal and axillary cymes, 5-25 cm (2.0-9.8 in.) long, with numerous blue to red-purple flowers. The flowers have a slender tube and abruptly spreading lobes, 12-22 mm (0.5-0.9 in.) across. This is a relatively large and showy plant, which is not difficult to identify.

  Habitat

Phlox maculata occurs in moist or wet prairies and wet meadow/carr communities. These are stable fire-maintained communities that develop over hundreds, if not thousands, of years. In many ways, P. maculata is a late successional species. It is not found in plowed fields, even decades after the fields have been abandoned. It also does not occur in habitats that have a history of livestock grazing or annual haying.

  Biology / Life History

Phlox maculata is a long-lived perennial that reproduces only by seed. The structure of the seeds does not suggest any specialized dispersal mechanisms, though the dispersal vector is likely one or more native animal species, rather than wind or water. Disturbance or large-scale perturbations of the habitat does not appear to be necessary to stimulate seed germination. Seeds seem capable of germinating and growing to maturity in a thick undisturbed prairie sod. However, the seeds may need a seasonal cycle of freeze and thaw in order to germinate. The flowers have a narrow corolla tube, making the nectar available only to long-tongued insects including butterflies, moths, and certain bee species.

  Conservation / Management

Management of P. maculata populations is basically an issue of habitat management. If the habitat in which it occurs is healthy and fully functional, then the resident population of P. maculata should persist indefinitely. A healthy habitat must include a viable community of insect pollinators as well as a diverse community of native plants to support them. Phlox maculata cannot be expected to survive isolated from the ecosystem processes in which it has evolved. 

It must be noted that P. maculata is very sensitive to livestock grazing and to competition from shrubs and trees. In this regard, livestock need to be kept out of the habitat at all times of the year. Tree and shrub encroachment can be controlled by mechanical cutting or fire or a combination of both. Controlled burns can be very helpful but should be conducted only in early spring, when the vegetation is still dormant. One published study (Calkins et al. 1996) found evidence that P. maculata is unusually sensitive to certain common herbicides used by the horticultural industry. Based on this sensitivity, it is recommended that herbicides be used with care or not at all in the vicinity of known populations of P. maculata.

  Best Time to Search

Within any viable population of P. maculata, some plants will likely be in flower between June 1 and August 15, with the peak probably around July 1; this is the best time to search.

  Authors/Revisions

Welby Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Calkins, J. B., B. T. Swanson, and D.L. Newman. 1996. Weed control strategies for field grown herbaceous perennials. Journal of Environmental Horticulture 14(4):221-227.

Michigan Natural Features Inventory. 2007. Rare Species Explorer [web application]. Michigan Natural Features Inventory, Lansing, Michigan.

Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the eastern broadleaf forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 394 pp.

Minnesota Department of Natural Resources. 2006. Tomorrow's habitat for the wild and rare: An action plan for Minnesota wildlife, comprehensive wildlife conservation strategy. Division of Ecological Services, Minnesota Department of Natural Resources. 297 pp. + appendices.

Minnesota Department of Natural Resources. 2009. Map of Minnesota's remaining native prairie 100 years after the public land survey. . Accessed 19 June 2009

NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia.