Basis for Listing

Erythronium propullans (dwarf trout lily) is an endemic spring ephemeral restricted to Rice, Goodhue, and Steele counties in southeastern Minnesota (Minnesota & Northeast Iowa Morainal and Paleozoic Plateau sections). It is the only known vascular plant endemic to Minnesota.  This remarkable wildflower was discovered in Rice County in 1870 near Faribault by Mary B. Hedges, a botany instructor at St. Mary’s School.  The following year, the species was described by Harvard botanist Asa Gray (1871). Preserving wild plants in their natural habitat appears to be the best option for ensuring survival of this rare species.  Habitat destruction has occurred across much of the species range through incompatible recreation uses, timber harvest, agriculture, and residential developments.  Erythronium propullans was listed as state endangered in 1984 and as federally endangered in 1986.

Listing at the endangered level is still warranted.  Annual monitoring of E. propullans since the late 1990s has seen the decline of some populations and the identification of several new threats. The new threats include invasive species and climate change impacts (Anderson 2018).

  Description

Erythronium propullans is a distinctive species, but it bears a superficial resemblance to E. albidum (white trout lily). The two species can be difficult to separate when in sterile form but are easily separated when in fruit or flower. The flowers of E. propullans are smaller than the flowers of E. albidum (often only 1.0 cm [0.4 in.] long) and are sometimes pinkish rather than white. They usually have 3, 4, or 5 tepals rather than the 6 tepals of E. albidum. Fruits of E. propullans are also smaller and, when mature, are nodding rather than erect. Offshoots of E. propullans arise not from the bulb, as in E. albidum, but from the stem above the bulb and mostly from flowering plants.

Only a small percentage of E. albidum plants will flower in any given year, approximately 3.8% (range 1.1-9.9%). On the other hand, E. propullans appears to flower at a higher rate, with an average of 13.8% (range 1-27%) flowering each season (Anderson 2018; Morley 1982). For this reason, if a carpet of non-flowering Erythronium leaves are seen covering a forest floor (a common sight in early spring) it is quite likely to be E. albidum.  If E. propullans were present, then flowers would likely be seen. The above-ground leaves and flowers wither and disappear as the summer progresses.

  Habitat

The habitat of E. propullans is most commonly a river terrace, mesic oak-basswood forest, or mesic maple-basswood forest on a north-facing slope above or near a stream. The plants typically occupy the lower to mid-portions of the slopes in these forests.  However, at some sites, plants have been documented nearly to the top of the slope or descending into the level floodplain below. These forests are a deeply shaded habitat in the summer, but E. propullans completes its life cycle in early spring before the trees leaf out.  Erythronium propullans occurs in colonies that range in size from one or two scattered plants to more than 500 individuals.  It is often intermixed with colonies of Erythronium albidum.

  Biology / Life History

The origin of this distinctive species is uncertain, but it is believed by Morley (1978) to have evolved in the vicinity of Faribault after the retreat of the glaciers 13,000 years ago. Because of its inefficient system of reproduction and dispersal, E. propullans has expanded its range very little and remains restricted to small portions of certain drainage systems in only three Minnesota counties. Published research reveals that E. propullans rarely, if ever, produces seeds (Banks 1980; Morley 1982). In fact, the only time fruits are produced is when the flowers are cross-pollinated with E. albidum (Banks 1980), giving rise to hybrids. It appears that this species reproduces largely, if not entirely, by asexual means through the production of offshoots. Attempts to artificially propagate this species have generally been unsuccessful.

In the early 2000s, plants were documented to exhibit abnormal floral morphology at a few populations. These features include the growth of leafy appendages from the flower pedicel, poorly developed tepals, larger than normal stamens, and a pad of undeveloped tissue at the end of the pedicel where the flower should be. The cause of these deformities is not known at this time.  The anomaly rates increased through the late 2000s. By the mid-2010s, apparent population crashes occurred in the colonies with the highest anomaly rates (Anderson 2018, Anderson & Sather 2011).

  Conservation / Management

Historically, habitat destruction occurred through timber harvest, conversion of floodplains to cropland, and grazing.  Present habitat loss is largely the result of incompatible recreation uses and residential developments. Populations have likely been impacted by the loss of Ulmus spp. (elm) in the canopy in terrace forests, earthworm infestations, over-use by White-tailed Deer (Odocoileus virginianus), and proliferation of invasive species such as Rhamnus cathartica (common buckthorn), Phalaris arundinacea (reed canary grass), and Alliaria petiolata (garlic mustard).  A changing climate is also affecting the species. Large-scale precipitation events have greatly altered the floodplain habitats harboring this rare wildflower.  These impacts include scouring away the finer textured soils in which the plant grows, deposition of 8-12 inches of sand on top of known populations, and the formation of new river channels through previously documented populations (Larson & Anderson 2016).

Soils on sites supporting E. propullans are generally quite erodible, and caution should be used in mechanical removal of invasive species to ensure that seedbeds are not created for their reintroduction and expansion. Limited chemical control of non-native invasive species may be possible during the fall when E. propullans and its companion native ephemerals are dormant and no longer above ground.

  Best Time to Search

The best time to search for Erythronium propullans is during the brief flowering period that usually extends 2-3 weeks from mid-April through mid-May.

  Conservation Efforts in Minnesota

Approximately half of the known E. propullans populations are now in the ownership of various public and private conservation organizations; however, active management has generally been lacking.  Long-term monitoring is underway at numerous sites to detect population trends and habitat changes.  The construction of a retaining wall and stream weirs along Prairie Creek at Nerstrand Big Woods State Park and a shoreline stabilization project on private land along the Cannon River have been undertaken to minimize bank erosion from flash flood events and loss of E. propullans habitat.

Captive populations of E. propullans that were introduced in Carver and Hennepin counties prior to the species’ listing as endangered may provide opportunities for further research and understanding of its biology and life history not afforded in a natural setting.

  Authors/Revisions

Derek S. Anderson and Welby R. Smith (MNDNR), 2020

(Note: all content ©MNDNR)

  References and Additional Information

Anderson, D. S. 2018. Summary of 2018 Erythronium propullans recovery activities. Minnesota Department of Natural Resources, St. Paul. 24 pp. +Appendix.

Anderson, D. S., and N. P. Sather. 2011. Minnesota Dwarf Trout Lily Recovery 2011. Minnesota Department of Natural Resources, St. Paul. 17 pp. +Appendix.

Banks, J. A. 1980. The reproductive biology of Erythronium propullans Gray and sympatric populations of E. albidum Nutt. (Liliaceae). Bulletin of the Torrey Botanical Club 107:181-188.

Converse, C., and W. Smith. 1984. Element stewardship abstract. The Nature Conservancy. Minneapolis, Minnesota.

Gray, A. 1871. A new species of Erythronium. American Naturalist 5:298-300.

Larson, K., and D. Anderson. 2016. Assessing the potential impacts of climate change on Minnesota Dwarf Trout Lily and Wood Turtle populations of southeastern Minnesota. Minnesota Department of Natural Resources, St. Paul. 10 pp.

Morley, T. 1978. Distribution and rarity of Erythronium propullans of Minnesota, with comments on certain distinguishing features. Phytologia 40:381-389.

Morley, T. 1982. Flowering frequency and vegetative reproduction in Erythronium albidum and E. propullans, and related observations. Bulletin of the Torrey Botanical Club 109(2):169-176.

Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis. 320 pp.

United States Fish and Wildlife Service. 1987. Minnesota Trout Lily (Erythronium propullans Gray) recovery plan. United States Fish and Wildlife Service, Twin Cities, Minnesota. 31 pp.