Rare Species Guide

  Synonyms

Xyris indica, Xyris bulbosa

  Basis for Listing

Xyris torta is perhaps most typical of the Atlantic Coastal Plain, but it also has a discrete inland range around the Great Lakes. This unusual distribution pattern has been documented in other species as well. According to McLaughlin (1932), it is thought to be the result of past climatic conditions that linked recently deglaciated habitats in the Midwest with similar ones on the coastal plain. This provided a migration route that allowed eastern species to colonize wet, sandy habitats inland. The migration route has long since receded and left relict populations isolated in the Great Lakes region, but the persistence of wet, sandy habitats in portions of the Midwest has allowed these isolated populations to survive. The only suitable habitat for this species in Minnesota occurs on the Anoka Sandplain in east-central Minnesota, a glacial outwash plain. Long-term climatic changes and the faster rates of climate change may cause a decline in the habitat for this species.

There are 5 historic collections of X. torta from Minnesota: 2 duplicate collections from Hennepin County dated 1889 with no specific recorded location and 3 Anoka County collections. Two of the known populations in Anoka County were destroyed by development in the 1960s. Intensive searches recently completed in Anoka County have located 3 additional populations, indicating that the species is still present in the state, but that it is very rare. Xyris torta was originally listed as a threatened species in Minnesota in 1984, but given its extreme rarity and habitat pressures, it was reclassified as endangered in 1996.

  Description

Xyris torta has small, inconspicuous, yellow flowers that are borne singly in the axils of scale-like bracts. Bracts are densely overlapping and form a compact head or spike, mostly 1-2.5 cm (0.4-1.0 in.) at maturity. Flowers are exserted, but sepals are hidden by the bracts. Two boat-shaped, lateral sepals are toothed and persistent, but the anterior sepal is larger and deciduous. There are 3 petals, 3 fertile stamens, 3 sterile stamens, and a 3-cleft style. The lustrous, dark green leaves are narrowly linear (20-50 cm x 2-5 mm; 7.9-10.7 in. x 0.08-0.2 in.), longitudinally grooved, and distinctly twisted (Gleason and Cronquist 1991).

  Habitat

This species appears to have very specific habitat requirements. Minnesota populations of X. torta occur primarily on wet, sandy shores of shallow lakes in the Anoka Sandplain and in sandy or peaty meadows or swales. These environments are typically open and sunny, with acidic soils and fluctuating water tables. Other rare species may be found in the same habitat, such as Polygala cruciata (cross-leaved milkwort), Rotala ramosior (tooth-cup), and Scleria triglomerata (tall nut-rush).

  Biology / Life History

Xyris torta is a short-lived perennial. It is insect-pollinated and reproduces only by seed.

The naked stems of X. torta may be visible throughout the year, even in winter if not covered by snow, but the species is easiest to find when in flower in July and August.

  Conservation / Management

It is quite unlikely that X. torta was ever abundant in Minnesota because its habitat is naturally so isolated and uncommon here. The outright destruction of populations and habitats as a result of rapid land development occurring in Anoka County is the major threat that has lead to this species' decline in Minnesota. The shallow wetlands are easily drained and converted to other uses. They may also be damaged by activities some distance away that change groundwater levels or drainage patterns. Alterations in the hydrology will almost certainly lead to changes in the vegetation community, including the invasion of non-native species such as Phalaris arundinacea (reed canary grass) or Lythrum salicaria (purple loosestrife). Prescribed fire may be a useful habitat management tool to help control woody plant invasion, but the surviving fragments of habitat harbor an unusually high number of rare species so the timing and frequency of prescribed burns should be carefully planned.

  Conservation Efforts in Minnesota

Conservation agreements are being pursued for land on which X. torta populations occur. Two of the sites are being actively managed with fire and other methods to preserve the rare species that occur there.

  References and Additional Information

Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. Second Edition. New York Botanical Garden, Bronx, New York. 910 pp.

Kost, M. A., and M. R. Penskar. 2000. Natural community abstract for coastal plain marsh. Michigan Natural Features Inventory, Lansing. 6 pp.

McLaughlin, W. T. 1932. Atlantic coastal plain plants in the sand barrens of northwestern Wisconsin. Ecological Monographs 2(3):335-383.