FWS Focus



Dwarf lake iris (Iris lacustris) is a species of the upper Great Lakes region, where it grows primarily along the edges of shoreline boreal forests in close association with, or proximity to, other rare coastal species, like Houghton’s goldenrod (Solidago houghtonii), Pitcher’s thistle (Cirsium pitcheri), piping plover (Charadrius melodus) and the Lake Huron locust (Trimerotropis huroniana), as noted in the 2013 recovery plan. Thomas Nuttall discovered dwarf lake iris in 1810 on Mackinac Island in Lake Huron, as noted by E.G.Voss in 1972. The U.S. Fish and Wildlife Service listed the dwarf lake iris as threatened on October 28, 1988 (53 FR 37972), under the provisions of the Endangered Species Act of 1973, as amended.

Scientific Name

Iris lacustris
Common Name
dwarf lake iris
FWS Category
Flowering Plants

Location in Taxonomic Tree


Identification Numbers



Characteristic category



Dwarf lake iris is found on the Great Lakes coasts, where it typically occurs in shallow soil over moist calcareous sands, gravel and beach rubble, and limestone crevices, as documented by E.G. Voss in 1972 and later by S.R. Crispin in 1981. It may occur semi-continuously for several miles along the lakeshore, interrupted only by local discontinuities in habitat, like rocky points, marshy bays, and areas modified by residential or other development, as S.R. Crispin also noted. S.R. Crispin also documented that this species also occurs sporadically on former beach ridges associated with retreating phases of post-glacial shorelines, with many occurrences persisting at significant distances inland and M.M. Makholm confirmed in 1986, as well as J.E. Van Kley in 1989.

Dwarf lake iris occurs predominantly on relatively young, raw, well drained soils with poorly developed horizons, noted J.E. Van Kley in 1989. They also noted that substrates range from sands and gravels to sandy clay loam and organic-enriched sands. Soil organic matter content varies by location, but most occurrences are found in moderate to high levels of organic matter, as documented by M.M. Makholm in 1986. They also noted that this species can tolerate a very broad range of nutrient levels and even does well at relatively low nutrient levels.

Light is one of the most critical factors in the growth and reproduction of dwarf lake iris, as documented by J.E. Van Kley and D.E. Wujek in 1993. Optimal vegetative growth and sexual reproduction are light dependent. Field observations by J.E. Van Kley in 1989, and other researchers over the years, have indicated that the most prolific flowering populations are those that receive a minimum threshold of direct sunlight for at least a portion of the day. Dwarf lake iris can survive at relatively low light levels, as long as some direct sunlight is available, as documented by M.M. Makholm in 1986. Dwarf lake iris populations may also respond positively to removal of the tree canopy, which increases light levels, though shaded conditions may prove more favorable during drought conditions, as documented by K. Doyle in 2015.


The land near a shore.

Characteristic category

Physical Characteristics

Color & Pattern

Dwarf lake iris flowers are most commonly blue, but may vary from pale to somewhat darker lilac shades. Albino flowers occur sporadically throughout the range of the species, as noted by J.E. Cruise and P.M. Catling in 1972. The floral tube is yellow.  The flowers have three sepals covered with whitish, multi-ridged crests splotched with yellow. Alternating with the sepals are three smaller, paler blue, erect petals (USFWS 2013).

Size & Shape

Dwarf lake iris is a low-growing perennial with very slender, creeping rhizomes. At their enlarged nodes, the rhizomes produce fans of flattened, sword-like leaves during the blooming period, as described by R.C. Foster in 1937. The showy flowers are borne singly on short flowering stalks with one to three reduced leaves at the base and scarious, meaning thin or papery, margined spathes, or bracts, that largely envelop the basal floral tube. The flowers, which emerge primarily from mid to late-May, have three, petal-like recurving sepals that are beardless. Overarching each sepal and stamen is a petal-like style branch with an upturned tip. On its underside, each style branch bears a thin, delicate, flap-like lip that comprises the stigmatic surface, as described in the 2013 recovery plan. The fruits are rounded capsules bearing brown, oval seeds with a shiny white, coiling appendage that may function as an elaiosome, meaning food body, to attract potential seed dispersers, as described by S.L. Planisek in 1983.

Leaf Height: 16 cm
Stalk Height: 4 cm
Flower Width: 2.5 to 4 cm
Flower Height: 4 to 6 cm
Fruit Length: 1.2 cm

Characteristic category

Life Cycle


Dwarf lake iris allocates a far lower percentage of resources to sexual than to vegetative reproduction, as noted in the 2013 recovery plan. Dwarf lake iris is a spring flowering perennial with branching, sub-surface rhizomes that are often partially above ground. These annually produce one to five ramets, or shoots, one of which may be sexual, or flower-bearing, while one to four, usually two, are vegetative, or sterile. Flowering ramets produce a single bisexual flower and are shorter than vegetative ramets. Flowering usually occurs from late April to early June, typically peaking from about mid-May to early June. Individual flowers remain open for one to three days, as S.L. Planisek documented in 1983 and J.E. Van Kley confirmed in 1989. They also documented that although dwarf lake iris is self-compatible, fruit set requires a pollen vector. B.M.H. Larson documented in 1998 that pollination vectors for this species include bee species from four families (Adrena carlini, Bombus vagans, Bombus impatiens, Bombus affinis, Augochlorella persimilis, Augochlorella striata and Hoplitis spp.), as well as the bee hawk-moth (Hemaris affinis) and a species of rove beetle and researchers from the Committee on the Status of Endangered Wildlife in Canada confirmed this in 2010, as did V. Brotske in 2018. Seed capsules for this species contain 20 to 22 seeds, each with an attached elaiosome, as documented by S.L. Planisek in 1983. Studies in Michigan and Wisconsin have shown ants (Formica spp.) will remove these seeds and play a role in seed dispersal, as documented by S.L. Planisek in 1983 and V. Brotske confirmed in 2018. Seeds are dormant at the time of dispersal and require several months of cold temperatures for germination, but can remain viable for at least 15 years within a soil bank, as documented by M.D. Morgan and A.T. Wolf in 2008. Seedlings can be distinguished from vegetative reproduction by the presence of a bright green loop at the top of the plant. This loop begins to shrivel within two weeks of emergence, as documented by V. Brotske in 2018.

Characteristic category

Similar Species

Similar Species

False asphodel (Tofieldia glutinosa) is a superficially similar species and a common native plant associate in shoreline fens that can be confused with dwarf lake iris in vegetative condition, but can be distinguished by its markedly narrower leaves and non-rhizomatous habit, as noted by the 2013 recovery plan.



Dwarf lake iris is endemic to the modern and ancient shorelines of northern lakes Huron and Michigan, where it ranges from the Door Peninsula of northeastern Wisconsin eastward through the Mackinaw Straits region, south to the Bruce Peninsula of Ontario, following the northern calcareous arc of Silurian and Devonian bedrock. Historical records indicate that it once occurred as far south as Milwaukee, Wisconsin and possibly along Detroit River near Sandwich, Ontario, as documented by the Committee on the Status of Endangered Wildlife in Canada in 2010. They also note that there are a total of 170 known extant occurrences: 89 in Michigan, 41 in Wisconsin and 40 in Ontario, as confirmed by the 2013 recovery plan and R.A. Hackett and others in 2021.

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