Bitter Fleabane (Trimorpha acris)

Not Seen in Minnesota in over 55 years!

by Lynden Gerdes, MBS Botanist/Ecologist

closeup of fleabane inflorescence
Bitter fleabane
Trimorpha acris
var. asteroides.photo by Lynden Gerdes

location of Bitter fleabane find
Bitter fleabane in northeastern MN

Bitter fleabane (Trimorpha acris (L.) Nesom var. asteroides (Anderz. ex Bess.) Nesom) - I had the good fortune to rediscover Bitter fleabane in 2000 after 55 years of no other reported observations. Bitter fleabane (Trimorpha acris), previously recognized as Erigeron acris, was first documented in 1929 from northern Cook County. It was later discovered at two additional locations in 1945 on the North Shore of Lake Superior in Cook County. None of these historic populations of plants have since been relocated. Complete list of vascular plants of Minnesota.

As part of my floristic investigations with the Minnesota  Biological Survey, I found Bitter fleabane in 2000 in the North Shore Highlands Ecological Subsection in Lake County on a west-facing, cobbly, forested slope adjacent to a prominent cliff. The historic populations of plants were apparently documented from the rocky shores and steep cliffs and talus facing Lake Superior. The most recent discovery is located two miles inland from Lake Superior's shore. Likely habitat for this species includes the shores, cliffs and talus of Lake Superior; and inland rock outcrops, rocky-wooded slopes, cliffs and talus. This species is also known to occur in clearings, open birch woods, and sandy shaded banks (Voss 1996).

The population discovered in 2000 was found in association with paper birch(Betula papyrifera), white cedar (Thuja occidentalis), balsam fir (Abies balsamea), red-raspberry (Rubus strigosus), fragrant fern (Dryopteris fragrans), fragile fern (Cystopteris fragilis) and rusty woodsia (Woodsia ilvensis). The Bitter fleabane plants were approximately 56 cm tall. Only seven flowering stems and approximately twelve sterile rosettes were observed.

Some distinguishing characteristics of the plant typically include: Stems and leaves that are very pubescent. Stems are leafy with the lower leaves narrowly tapered to the base and much longer than the upper leaves (9-11 cm vs. 2-4 cm). The inflorescence is racemose with about 10 heads that are each about 1 cm wide. Unlike most fleabanes and asters in our area, this species does not have obvious ray flowers. One can easily walk by the plants incorrectly assuming they are one of our common composites at either an immature or more mature stage of development.

Status in Minnesota - Bitter fleabane is listed as a Special Concern species in the State.

Bitter fleabane on rocky slope
Bitter fleabane on a rocky slope.
photo by Lynden Gerdes

This single site in Lake County is the only known location of the species in the state. Its state status is currently under review as part of the update of the Minnesota list of Endangered, Threatened, or Special Concern species (128kb). If you are so fortunate to encounter this species during one of your botanical treks, please record its location and contact the Minnesota Biological Survey or the Natural Heritage and Nongame Research Program for additional information.


REFERENCES Voss, E. G. 1996. Michigan Flora Part III Dicots (Pyrolaceae-Compositae). Cranbrook Inst. Sci. Bull. 61 and the Univ. of Michigan Herbarium. 622 pp.