Rare Species Guide

  Synonyms

Eleocharis parvula var. anachaeta

  Basis for Listing

There are only three authenticated specimens (and one questionable specimen) of Eleocharis coloradoensis from Minnesota and the most recent is dated 1945 (Ownbey and Morley 1991). Repeated attempts to locate an extant population have failed. If the species still exists in Minnesota, it must be very rare. The cause of its evident decline is quite clear - loss of habitat. Appropriate habitat includes the shores of prairie lakes in western Minnesota; specifically, those lakes that still posses their original shoreline and maintain a somewhat natural seasonal fluctuation of water level. This type of habitat has plummeted in recent decades. Most shallow prairie lakes were drained to create crop fields, and those lakes that were too deep to be drained were often degraded by having drain water from crop fields channeled into them. The present status of special concern recognizes the extreme rarity of E. coloradoensis in the state, and at the same time acknowledges the lack of current information.

  Description

Eleocharis coloradoensis is a small, perennial spike-rush with numerous soft, thin stems no more than about 10 cm (3.9 in.) long. At the tip of each stem is a 3-6 mm (0.12-0.24 in.) long spikelet with 6-25 small flowers. Each flower is subtended by a bright, orange-brown scale 1.7-2.5 mm (0.07-0.10 in.) long. The seeds (achenes) are brown, obovoid to obpyriform in shape, thickly 3-sided, 0.75-1.1 mm (0.03-0.04 in.) long, and 0.55-0.7 mm (0.02-0.03 in.) wide. The tip of the seed is narrowly truncate or tapered into a small tubercle or protuberance 0.05-0.2 mm (0.002-0.008 in.) tall and 0.15 mm (0.006 in.) wide (Smith et al. 2002). The plant will produce underground rhizomes, which may have small tubers at their tips. There are 16 species of Eleocharis in Minnesota. Attempting to distinguish the various species can be very difficult and will usually require mature seeds (achenes) and a microscope that has a magnification of at least 30x.

  Habitat

Because of the paucity of records, there is some uncertainty about the habitat of E. coloradoensis in Minnesota. The best assessment from historical specimens indicates it occurs on exposed muddy or silty lake shores in the prairie region of western Minnesota. Such habitats are seasonal in nature, meaning they develop in mid or late summer when reduced rainfall causes the shores of shallow lakes to recede, thereby exposing a moist, sparsely vegetated zone around the margin of the lake.

  Biology / Life History

Based on the small size of E. coloradoensis and the sparsely vegetated habitats where it is believed to occur, it is perhaps reasonable to say it is intolerant of competition from larger plants. It is also likely that it needs direct sunlight and a soft, moist substrate. Eleocharis coloradoensis is a perennial, but individual plants may not live long. Its survival strategy may rely on rapid growth and reproduction resulting in a high level of recruitment rather than longevity.

Eleocharis coloradoensis is known to produce small tubers at the tips of underground rhizomes, a feature that is uncommon among spike-rushes. Tubers are vegetative reproductive structures and each is capable of growing into a new plant separate from the parent plant. These tubers may remain near the parent plant, or it is possible they may float on water currents or be carried by small animals to new sites, possibly even different lakes or watersheds. The seeds are also capable of a certain amount of mobility although they posses no specialized structures for dispersion.

The best time to search for E. coloradoensis is when the achenes are mature during the months of August and September.

  Conservation / Management

At this time there are no known extant populations of E. coloradoensis in Minnesota, so it would be premature to propose a management plan. However, because of the small size of the plant, the ephemeral nature of its habitat, and the difficulty in distinguishing one species of spike-rush from another, it seems quite possible that viable populations have been overlooked. If this species is found in Minnesota again, it will likely be on the shore of a shallow prairie lake or pond where hydrologic issues will need to be addressed. Most likely the issues would relate to management of inlets, outlets, drain tiles, nutrient inputs, rip-rap, public access, or exotic species control.

  Conservation Efforts in Minnesota

Because no extant populations of E. coloradoensis have been found in Minnesota, no conservation efforts have been directed towards this species.

  References and Additional Information

Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis. 320 pp.

Smith, S. G., J. J. Bruhl, M. S. Gonzalez-Elizondo, and F. J. Menapace. 2002. Eleocharis. Pages 60-120 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 23. Oxford University Press, New York, New York.

Smith, W. R. 2018. Sedges and rushes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 696 pp.