Iris lacustris

Dwarf Lake Iris

FWS Focus

Overview

Characteristics
Overview

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, such as Houghton’s goldenrod (Solidago houghtonii), Pitcher’s thistle (Cirsium pitcheri), piping plover (Charadrius melodus), and the Lake Huron locust (Trimerotropis huroniana) (USFWS 2013). Thomas Nuttall discovered dwarf lake iris in 1810 on Mackinac Island in Lake Huron (Voss 1972). This attractive shoreline species is among the best known of all the endangered and threatened plants of the Great Lakes region, where it has become a symbol of plant rarity and conservation in both Michigan and Wisconsin. In 1998, Michigan designated the dwarf lake iris as the official State wildflower. 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.

USFWS. 2013. Dwarf Lake Iris (Iris lacustris) Recovery Plan. United States Fish and Wildlife Service. Bloomington, Minnesota.

Voss, E. G. 1972. Michigan Flora, Part I. Gymnosperms and Monocots. Cranbrook Institute of Science, Bloomfield Hills, MI. Bulletin 55.

Scientific Name

Iris lacustris
Common Name
dwarf lake iris
FWS Category
Flowering Plants
Kingdom

Location in Taxonomic Tree

Genus
Species

Identification Numbers

TSN:

Characteristics

Characteristic category

Physical Characteristics

Characteristics
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 (Foster 1937).  The showy flowers are borne singly on short flowering stalks with one to three reduced leaves at the base and scarious (thin, papery)-margined spathes (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 (USFWS 2013). The fruits are rounded capsules bearing brown, oval seeds with a shiny white, coiling appendage that may function as an elaiosome (food body) to attract potential seed dispersers (Planisek 1983).

Measurements

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

Foster, R. C. 1937. A cyto-taxonomic study of the North American species of Iris. Contributions from the Gray Herbarium of Harvard University, No. CXIX.

Planisek, S. L. 1983. The breeding system, fecundity, and dispersal of Iris lacustris. Michigan Botanist 22: 93-102.

USFWS. 2013. Dwarf Lake Iris (Iris lacustris) Recovery Plan. United States Fish and Wildlife Service. Bloomington, Minnesota.

Color & Pattern

Dwarf lake iris flowers are most commonly blue but may vary from pale to somewhat darker lilac shades, and albino flowers occur sporadically throughout the range of the species (Cruise and Catling 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).

Cruise, J. E. and P. M. Catling. 1972. A white-flowered form of Iris lacustris from Ontario. Rhodora 74: 271.

USFWS. 2013. Dwarf Lake Iris (Iris lacustris) Recovery Plan. United States Fish and Wildlife Service. Bloomington, Minnesota.

Characteristic category

Habitat

Characteristics
Habitat

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 (Voss 1972; Crispin 1981). It may occur semi-continuously for several miles along the lakeshore, interrupted only by local discontinuities in habitat, such as rocky points, marshy bays, and areas modified by residential or other development (Crispin 1981). Dwarf lake iris also occurs sporadically on former beach ridges associated with retreating phases of post-glacial shorelines, with many occurrences persisting at significant distances inland (Crispin 1981; Makholm 1986; Van Kley 1989).

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

Light is one of the most critical factors in the growth and reproduction of dwarf lake iris (Van Kley and Wujek 1993). Optimal vegetative growth and sexual reproduction are light dependent. Field observations 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 (Van Kley 1989; Morgan and Wolf 2008).  Dwarf lake iris can survive at relatively low light levels, as long as some direct sunlight is available (Makholm 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 (Doyle 2015).

Crispin, S. R. 1981. Iris lacustris in Michigan. Natural Features Inventory, Unpublished Report.

Doyle, K. 2015. 2015 Annual Progress Report: Monitoring Fassett’s Locoweed, Eastern Prairie Fringed Orchid, and Dwarf Lake Iris. Report to USFWS. Wisconsin Department of Natural Resources, Madison, WI.

Makholm, M. M. 1986. Ecology and management of Iris lacustris in Wisconsin. M.S. Thesis, University of Wisconsin-Madison.

Morgan, M. D. and A. T. Wolf. 2008. A long-term study of the reproductive biology of dwarf lake iris (Iris lacustris) in northeastern Wisconsin. Unpublished manuscript, University of Wisconsin-Green Bay.

Van Kley, J. E. 1989. Habitat and ecology of Iris lacustris (the dwarf lake iris). M.S. Thesis, Central Michigan University.

Van Kley, J. E. and D. E. Wujek. 1993. Habitat and ecology of Iris lacustris (the dwarf lake iris). Michigan Botanist 32: 209-222.

Voss, E. G. 1972. Michigan Flora, Part I. Gymnosperms and Monocots. Cranbrook Institute of Science, Bloomfield Hills, MI. Bulletin 55.

Coastal

The land near a shore.

Characteristic category

Life Cycle

Characteristics
Reproduction

Dwarf lake iris allocates a far lower percentage of resources to sexual than to vegetative reproduction (USFWS 2013). 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 (shoots), one of which may be sexual (flower-bearing) while one to four (usually two) are vegetative (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 (Planisek 1983, Van Kley 1989). Although dwarf lake iris is self-compatible, fruit set requires a pollen vector (Planisek 1983, Van Kley 1989). Pollination vectors include bee species from 4 families (Adrena carlini, Bombus vagans, Bombus impatiens, Bombus affinis, Augochlorella persimilis, Augochlorella striata, and Hoplitis spp.), the bee hawk-moth (Hemaris affinis), and a species of rove beetle (Larson 1998, COSEWIC 2010, Brotske 2018). DLI seed capsules contain 20-22 seeds, each with an attached elaiosome (Planisek 1983). Studies in Michigan and Wisconsin have shown ants (Formica spp.) will remove these seeds and play a role in seed dispersal (Planisek 1983, Brotske 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 (Morgan and Wolf 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 2 weeks of emergence (Brotske 2018).

Brotske, V. 2018. Pollination, Seed Dispersal, Germination, And Seedling Survival in the Federally Threatened Dwarf Lake Iris (Iris lacustris). M.S. Thesis, University of Wisconsin-Green Bay.

COSEWIC. 2010. COSEWIC Assessment And Status Report On The Dwarf Lake Iris Iris lacustris in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa.

Larson, B. M. H. 1998. Visitation of the Endemic Dwarf Lake Iris, Iris lacustris, by Halictid Bees, Augochlorella striata. Canadian Field Naturalist 112(3): 522-523.

Morgan, M. D. and A. T. Wolf. 2008. A long-term study of the reproductive biology of dwarf lake iris (Iris lacustris) in northeastern Wisconsin. Unpublished manuscript, University of Wisconsin-Green Bay.

Planisek, S.L. 1983. The Breeding System, Fecundity, and Dispersal of Iris lacustris. The Michigan Botanist 22: 93-102.

USFWS. 2013. Dwarf Lake Iris (Iris lacustris) Recovery Plan. United States Fish and Wildlife Service. Bloomington, Minnesota.

Van Kley, J. E. 1989. Habitat and ecology of Iris lacustris (the dwarf lake iris). M.S. Thesis, Central Michigan University.

Characteristic category

Similar Species

Characteristics
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 (USFWS 2013).

USFWS. 2013. Dwarf Lake Iris (Iris lacustris) Recovery Plan. United States Fish and Wildlife Service. Bloomington, Minnesota.

Geography

Characteristics
Range

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 (COSEWIC 2010).  There are a total of 170 known extant occurrences: 89 in Michigan, 41 in Wisconsin, and 40 in Ontario (COSEWIC 2010, USFWS 2013, Hackett et al. 2021).

COSEWIC. 2010. COSEWIC Assessment and Status Report on The Dwarf Lake Iris Iris lacustris in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa.

Hackett, R.A., A. Klain, J. Spiels, L. Kirkpatrick, P.J. Higman. 2021. Dwarf Lake Iris Recovery and Population Monitoring. Report No. 2021-07. Michigan Natural Features Inventory, Lansing, MI.

USFWS. 2013. Dwarf Lake Iris (Iris lacustris) Recovery Plan. United States Fish and Wildlife Service. Bloomington, Minnesota.

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