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Endangered Species Program
Conserving and restoring threatened and endangered species and their ecosystems
Minnesota Dwarf Trout Lily (Erythronium propullans)
This information is taken from Biological Report #18 of the Minnesota Natural Heritage and Nongame Wildlife Programs, Minnesota Department of Natural Resources; prepared in cooperation with the U.S.Fish and Wildlife Service.
The Minnesota dwarf trout lily is an endangered species. Endangered species are animals and plants that are in danger of becoming extinct. Identifying, protecting, and restoring endangered and threatened species is the primary objective of the U.S. Fish and Wildlife Service's endangered species program.
What is the Minnesota Dwarf Trout Lily?
The dwarf trout lily occurs on fewer than 600 acres of woodland habitat, rich slopes dominated by maple and basswood and adjoining floodplains dominated by elm and cottonwood. Like spring beauties and dutchman's breeches, trout lilies are "spring ephemerals," adapted to flower and grow before the deciduous trees develop their leaves. When summer shade darkens the forest floor these plants have already bloomed, generated their food reserves for the coming year and lost their leaves.
Why Is the Dwarf Trout Lily Rare?
The rarity of the dwarf trout lily is probably partially explained by its unusual mode of reproduction. Trout lilies often reproduce by producing offset runners. It was formerly believed that dwarf trout lilies did not set seed and that populations increased only when each flowering plant produced one runner with a new bulb. However, recent studies show that population increase is sometimes too rapid to be accounted for only by a single runner borne on flowering plants. Many populations set seed, but seed viability remains unknown at present, nor do we know whether the seeds will produce dwarf trout lilies or hybrids with common white trout lilies. Some known dwarf trout lily colonies are almost exclusively dominated by large beds of sterile leaves.
The origin of the Minnesota dwarf trout lily is not fully known, but genetic research suggests it evolved from the white trout lily shortly after the last glaciation. It is likely that the plants were spread by floodwaters uprooting them from an original location somewhere on the uplands between the Cannon and Zumbro rivers. Torn loose from their original habitat, these plants would have been redeposited on slopes and floodplains downstream. Perhaps this mode of dispersion explains the plant's limited geographic distribution at elevations of 960 to 1000 feet within the Cannon River watershed and tributaries.
How is the Dwarf Trout Lily Endangered?
The dwarf trout lily was listed as a federally endangered species because it is jeopardized with the possibility of extinction. This is a plant that has probably always been rare; it is presently known to occur in only three counties in Minnesota. Such a narrow range allows little leeway for a wild species to adapt to new threats or changing environmental conditions. Today housing developments, increased pressure for recreational land use, abnormal flower development and the challenge of controlling expanding populations of exotic invasives like garlic mustard increase the chances that the few remaining populations could be destroyed.
In addition to direct destruction of plants by human activities, increased conversion of floodplains to cropland reduces the probability that plants dislodged by upstream floodwaters will find suitable downstream habitat. Disturbance of uphill areas can cause erosion and siltation in areas where the lilies occur.
Why Be Concerned About the Minnesota Dwarf Trout Lily?
Like all native species, the Minnesota dwarf trout lily has its own specific niche in the ecosystem and relationships to other plants and animals with which it lives. As such, it is a part of the whole, a part whose unknown utility is best expressed in the words of Wisconsin conservationist Aldo Leopold: "The first rule of intelligent tinkering is to save all the parts.
The Minnesota dwarf trout lily possesses a genetic and chemical makeup unlike that of any other plant. It is known to be most genetically similar to the closely related white trout lily from which it is believed to have evolved no more than 9000 years ago.
The unique genetic information in each species is potentially valuable to all of us. Alkaloids from many wild plants are active ingredients in medicines and other useful products. Loss of the dwarf trout lily would eliminate forever the potential for such benefits
What Does the Minnesota Dwarf Trout Lily Look Like?
There are three species of trout lily in Minnesota: the Minnesota dwarf trout lily, the white trout lily (Erythronium albidum), and the yellow trout lily (Erythronium americanum). All are spring ephemerals. All have tapering green leaves lightly mottled with a greyish-white pattern. Huge patches of leaves with very few flowers are characteristic of trout lilies and are common in all three species.
The leaves of white trout lilies and dwarf trout lilies are very similar and often overlap in size. Therefore, it is difficult, if not impossible, to distinguish between species in large masses of leaves without flowers. However, flowering dwarf trout lilies are distinguished by the very small size of their flowers. Flowers of the dwarf trout lily are about the size of a dime or less, pale pink, with a variable number of perianth parts ("petals"). Most members of the lily family have 6 "petals", but dwarf trout lilies may have four, five or six. Typically, dwarf trout lily pedicels (“stems”) are about the width of a pencil line, whereas those of white trout lilies are approximately 1 mm wide (closer to the diameter of string or a rubber band).
Where is the Dwarf Trout Lily protected?
Approximately half of the known dwarf trout lily sites are included in state Scientific and Natural Areas, sate or county parks or private preserves such as those of The Nature Conservancy.
A large number of dwarf trout lily populations occur on private land where farmers or other landowners have maintained the species by protecting its woodland habitat. many of these families have entered into a voluntary private registry program that acknowledges their role in preserving the state's rarest plant species.
How are Dwarf Trout Lily preserves managed?
The Minnesota dwarf trout lily's woodland habitat is a mature self-perpetuating forest ecosystem that requires little or no manipulation of the vegetation. For this reason most management activities are directed toward protecting dwarf trout lily colonies from erosion caused by upstream activities or from direct damage caused by human traffic. Preserves are closed to motorized traffic to prevent soil compaction or disturbance.
The boardwalk at Nerstrand Woods Sate Park was constructed to allow visitors to observe and photograph the Minnesota dwarf trout lily without disturbing colonies of this endangered plant.
A retaining wall was constructed to stabilize the bank of Prairie Creek at Nerstrand Woods State Park, where spring flood waters were undermining dwarf trout lily colonies.
Last updated: October 10, 2018