Rare Species Guide

  Synonyms

Rudbeckia triloba

  Basis for Listing

Rudbeckia triloba var. triloba (three-leaved coneflower) reaches the northern limit of its natural range in southeastern Minnesota, where it occurs in mesic hardwood and floodplain forests. When the species was listed as special concern in 1984, there were only five records in Minnesota and all were pre-1961. There was also uncertainty over the origin of the two records from Olmsted and Blue Earth counties. It was thought possible that they had escaped from artificial plantings and were not actually native to the state. Due to this uncertainty, the species was given a status of special concern.

Since that time, a systematic biological inventory of the region resulted in the discovery of only five native populations, all in Houston and Mower counties (Eastern Broadleaf Forest). There appears to be potential habitat in Fillmore and Winona counties, yet the species has never been found there. With the rarity of the species in Minnesota reasonably confirmed, and threats to its habitat well-documented, the status of R. triloba var. triloba was elevated to threatened in 2013.

  Description

Rudbeckia triloba var. triloba is variously described as a short-lived perennial, an annual, or sometimes a biennial. Stems can reach 1.6 m (5.2 ft.) tall, though they usually attain a height of no more than about 1 m (3.3 ft.). The younger leaves may be entire and cordate; the older leaves (those lower on the stem) are often 3-lobed. This 3-lobed character is the feature that most easily distinguishes R. triloba var. triloba from other species. The flowering heads have 6-12 yellow or orange rays, which are 1-2 cm (0.4-0.8 in.) long, and a black-purple disk, which is 5-13 mm (0.5 in.) across (Urbatsch and Cox 2006).

  Habitat

Recent Minnesota records of R. triloba var. triloba are from mesic hardwood forests and floodplain forests, particularly where stream beds or other ecotones create canopy gaps, allowing more light to reach the forest floor. Soils tend to be moist and loamy, though soils along a stream may be silty.

  Biology / Life History

Little is known about this species in Minnesota. Populations are notably small, often only 10-15 plants are found in one small area. This seems to be true even where more habitat is available. These colonies or groupings of plants may be somewhat transient. Certainly the individual plants are short lived. Microhabitats might also be interpreted as somewhat transient. This is because maintenance of the desired ecotones, where the canopy is thinner and more light reaches the ground layer, may be reliant on unpredictable stochastic events.

  Conservation / Management

Since settlement times, large expanses of floodplain forests in southern Minnesota have been lost due to conversion to agriculture and urbanization as well as the damming and channelization of rivers. This trend is continuing, and habitat loss and degradation still pose an eminent threat to the species. The invasion of aggressive non-native species, particularly Rhamnus cathartica (common buckthorn), Lonicera spp. (Eurasian honeysuckle shrubs), and Alliaria petiolaris (garlic mustard) is also a serious concern.

It should be noted that R. triloba var. triloba is a popular and widely sold garden plant. Occasionally, it is found near an abandoned garden or in an old field and thought to be native. Usually such plants originated from a garden supplier in another state and consequently have no conservation value in Minnesota. Only native plants growing in native habitats qualify as "threatened" in Minnesota. However, since the native and the non-native plants do look alike, it might be difficult to tell them apart. It is important to evaluate the habitat, the geographic location, the population structure, and local history in order to determine whether a population is native or not.

  Best Time to Search

The best time to search for R. triloba var. triloba is when it is in flower, during August and September.

  Authors/Revisions

Welby Smith (MNDNR), 2008 and 2018

(Note: all content ©MNDNR)

  References and Additional Information

Coffin, B., and L. Pfannmuller, editors. 1988. Minnesota's endangered flora and fauna. University of Minnesota Press, Minneapolis. 473 pp.

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, Division of Ecological Resources. 2008. Rare species guide: an online encyclopedia of Minnesota's rare native plants and animals [Web Application]. Minnesota Department of Natural Resources, St. Paul, Minnesota. Accessed 1 July 2009.

Urbatsch, L. E., and P. B. Cox. 2006. Rudbeckia. Pages 44-60 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 21. Oxford University Press, New York, New York.