Synonyms

Euphorbia missurica var. intermedia, Chamaesyce missurica

  Basis for Listing

Euphorbia missurica (Missouri spurge) occurs primarily on the Great Plains to the west and south of Minnesota. It is not considered to be a dominant species in any major habitat type, although it is reported to be locally common in some marginal habitats (Great Plains Flora Association 1986). It appears that a portion of west central and southwestern Minnesota fall within the geographic range of the species and could provide suitable habitats. There is considerable uncertainty in this assessment and, in fact, the species' status in Minnesota is an unsolved mystery that botanists are trying to unravel.

Euphorbia missurica was found at three sites in Otter Tail County between 1892 and 1936, but nowhere before or since. It seems highly probable that this species occurred naturally in the prairie region of western Minnesota prior to settlement, although it must have been very rare. Despite 75 years having passed since the last recorded observation of E. missurica, it is still possible that it occurs in Ottertail County or elsewhere in Minnesota. Its superficial similarity to several other common native and weedy non-native members of the spurge family make it possible, or even likely, that it has just been overlooked. However, the significant loss of prairie habitat is certainly a limiting factor for the species. Euphorbia missurica was listed as a special concern species in Minnesota in 1996.

  Description

Euphorbia missurica is an annual with smooth stems that may stand erect at first and then become decumbent when they reach full size. Full size stems can be as much as 65 cm (2.1 ft.) in length but probably average less than 20 cm (7.9 in.). The leaf blades are 1-3 cm (0.4-1.2 in.) long and 1-5 mm (0.04-0.20 in.) wide, oblong to linear in shape, and they have smooth margins. The petioles are 1-3 mm (0.04-0.12 in.) long and have distinct linear stipules. What appears to be the flower is actually a cluster of greatly reduced and simplified flowers called a cyathium. In this species, each cyathium has 29-48 male flowers surrounding a single female flower. Each cyathium is on a stalk (peduncle) 1-11 mm (0.04-0.43 in.) long, and is solitary in the axils of the leaves, or sometimes arranged in a terminal inflorescence comprised of 3-5 cyathia. Each cyathium is 1.7-1.9 mm (0.067-0.075 in.) across and has triangular lobes with glands in the sinuses. The glands are circular or oblong in outline. The ciathia also have small, but conspicuous, white or pink appendages that simulate petals. The seed capsules are 2-2.5 mm (0.08-0.10 in.) long (Wheeler 1941).

  Habitat

On the Great Plains, which is perhaps the core of its range, E. missurica is reported to occur in a variety of dry, sandy or rocky prairie habitats (Great Plains Flora Association 1986). Its habitat in Minnesota is somewhat open to speculation. It may be similar to that of the Great Plains, although it should probably be expanded to include sandy lake shores. There are over 10,000 lakes in Minnesota, but the only lakes with a reasonable chance of harboring a population of this species are the few that occur in the original prairie region in the western part of the state, especially the southwestern part. The most likely habitat is the narrow zone between the normal low water line and the normal high water line on gently sloping, sparsely vegetated beaches. This is the classic zone occupied by annual plant species, including several common species that are closely related to E. missurica.

  Biology / Life History

Very few details are known about the biology of E. missurica. In general, it is known to be an insect-pollinated annual that inhabits dry, sunny, sparsely vegetated habitats. Some of these habitats may support early successional or disturbance-dependent plant communities. Fire is the most likely source of disturbance for prairie communities although grazing or digging animals may also play a role. Lake shore communities may be sustained by fluctuations in water levels during the summer or ice scouring during the winter. Like many, or perhaps most annual species, E. missurica is known to maintain a multi-year seed bank in the soil (Abrams 1988), although it is not known what role a seed bank may play in the ecology of populations.

The best time to search for E. missurica is when it is flower, from about mid-July through September.

  Conservation / Management

An effort should be made to relocate E. missurica in Minnesota. A search could begin with sandy lake shores in Otter Tail County, preferably in late summer of a dry year when the lake levels are at a low point. Low lake levels would expose a maximum of shoreline, thereby creating a maximum of potential habitat for E. missurica. It is also possible that E. missurica could occur in dry, sandy habitats that are not associated with lake shores, such as prairies or thinly forested ridges.

  Conservation Efforts in Minnesota

Because E. missurica has not been seen in Minnesota since 1936, no conservation efforts have been directed towards this species.

  References and Additional Information

Abrams, M. D. 1988. Effects of burning regime on buried seed banks and canopy coverage in a Kansas tallgrass prairie. The Southwest Naturalist 33(1):65-70.

The Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence. 1,402 pp.

Wheeler, L. C. 1941. Euphorbia subgenus Chamaesyce in Canada and the United States exclusive of southern Florida. Rhodora 43:97-286.