Rare Species Guide

  Basis for Listing

As of 2015, there were about 20 sites of Elatine triandra (three-stamened waterwort) occurring in Minnesota from two distinct habitat types and geographical ranges. Approximately half of them are from shallow rock pools in the southwestern portion of the state (Prairie Parkland Province). These habitats have been under considerable pressure from agricultural activities (cattle grazing, herbicide application) and rock quarrying, and it seems likely that they have undergone a significant decline within historical times. At the time of this writing (2017), the long-term viability of these populations is uncertain.

The remainder of the known populations are in clear soft-water lakes in the north central and northeastern portion of the state (Laurentian Mixed Forest Province). Extensive botanical searches have found E. triandra in less than one percent of Minnesota lakes (13 lakes out of 2,025 searched). This history clearly qualifies E. triandra as an extremely rare species in Minnesota; hence, it was designated a species of special concern in 2013.

  Description

Elatine triandra is an aquatic plant, though it is adapted to more than one type of habitat. When growing in shallow water or mud flats, it may be no more than a few centimeters tall; whereas, when growing in deeper water, the stems can be one meter (3.3 ft.) or more in length. In all cases, the leaves are opposite on the stem, linear to obovate in shape, and less than 8 mm (0.3 in.) long. The tiny flowers occur singly in the leaf axils and have 3 petals and 3 sepals. The flowers, however, have been reported to be cleistogamous, meaning the petals and sepals never fully develop (Duncan 1964). Distinguishing E. triandra from E. minima (small waterwort), the only other species of Elatine in Minnesota, requires an examination of its fruits, which, as the name implies, are 3-lobed. The fruits are found in the axils of the leaves. Magnification may be required to see this feature.

  Habitat

In the forested region of the state (Laurentian Mixed Forest Province), E. triandra occurs in clear nutrient-poor lakes in shallow water (0.5-1 m [1.5-3 ft.]) with a sandy substrate. Water chemistry at one such site was recorded as 29 ppm total alkalinity, with a pH of 7.5. In the southwest portion of Minnesota (North Central Glaciated Plains Section), E. triandra occurs in small rock pools, which typically become dry by early June. When the water evaporates, the plants persist for a few more weeks in the drying mud on the bottom of the former pool. The plants disappear once the mud becomes desiccated.

  Biology / Life History

There appears to be two life forms of E. triandra (Fernald 1941). It is, at times, a submerged aquatic, which can complete its life cycle underwater. In this situation, the flowers are primarily or entirely cleistogamous (Duncan 1964), meaning they are self-pollinated. Yet E. triandra can also survive and reproduce if stranded on wet sand or mud at the edge of a pond or lake. In its terrestrial phase, the flowers become chasmogamous, meaning they open fully and are pollinated by flying insects. 

It is known that E. triandra is an annual, which is rather unusual since most aquatic plants are perennial. As an annual, E. triandra reproduces only by seed; it does not produce tubers, rhizomes, or any other perennial vegetative structure. Based on observations in Minnesota, seeds of E. triandra can probably survive a period of desiccation and still germinate the following year. It is also possible that a period of desiccation or exposure to the air may even enhance germination. Although the method of seed dispersal is uncertain, it likely employs water currents and possibly amphibious animals.

  Conservation / Management

Populations of E. triandra that occur in north central and northeastern Minnesota are found in shallow portions of large or medium size lakes. Any management activity that maintains or enhances water quality, shoreline stability, and species diversity ought to have a positive effect on E. triandra. Populations of E. triandra in southwestern Minnesota occur in shallow rock pools and possibly prairie ponds. These habitats have declined dramatically within historic times (both in quantity and quality), and it is assumed that populations of E. triandra have declined in rough proportion to the decline of their habitat. Efforts should be made to continue to identify potential habitats in southwestern Minnesota and to determine the status of known and newly discovered populations.

  Best Time to Search

The annual development of E. triandra in shoreline habitats may be dependent on water levels; therefore, predicting search dates is difficult. The most productive dates are probably during the months of July and August.

  Conservation Efforts in Minnesota

In 2007, the Renville and Redwood County Soil and Water Conservation Districts, in association with state and federal agencies, coordinated an initiative to compensate interested landowners for permanently protecting the most ecologically intact rock outcrops and associated wetlands in those two counties. In 2009, the initiative was expanded to encompass five counties in the Upper Minnesota River Valley (Protection of Granite Rock Outcrop Ecosystem). By 2012, approximately 227 ha (560.4 acres) were enrolled into perpetual conservation easements as a result of this initiative, and E. triandra is one of the rock outcrop species most likely to benefit from the program. Conservation plans, which outline conservation practices, such as removal of invasive species and livestock exclusion, were developed for each of the easement sites. Habitat maintenance and improvement measures, such as prescribed burning, fencing, rotational grazing, and/or seeding were also included in the plans.

  Authors/Revisions

Welby Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Duncan, W. H. 1964. New Elatine (Elatinaceae) populations in the southeastern United States. Rhodora 66:47-53.

Fernald, M. L. 1941. Elatine americana and E. triandra. Rhodora 43(509):208-211.

Harris, F. 2009. Rock pools on the prairie: ephemeral pools on the prairie form amazing mini-ecosystems. Minnesota Conservation Volunteer 72(423):30-39.

Harris, F. 2010. Recent rediscovery of rare plants of ephemeral rainwater pools in Sioux quartzite prairies in southwestern Minnesota. Pages 105-109 in Proceedings of the 22nd North American Prairie Conference: restoring a national treasure. D. Williams, B. Butler, D. Smith, editors. August 1-5, 2010, University of Northern Iowa, Cedar Falls.

Minnesota County Biological Survey. 2007. Native plant communities and rare species of the Minnesota River Valley counties. Division of Ecological Resources, Minnesota Department of Natural Resources, St. Paul. 153 pp.

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.

Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the prairie parkland and tallgrass aspen parklands provinces. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 362 pp.

NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia.

Wisconsin Department of Natural Resources. 2007. Longstem Water-wort (Elatine triandra) factsheet. <http://dnr.wi.gov/topic/endangeredresources/Plants.asp>. Accessed 25 June 2009.