Basis for Listing

In the past 20 years, aquatic plant surveys have been completed on over 2,000 lakes throughout Minnesota; Alisma gramineum (narrow-leaved water plantain) has been found in only 16 of those lakes. This indicates a fairly high degree of rarity. More lake surveys are scheduled for the future, though there is no reason to believe that A. gramineum will be found more frequently in the future than it has to date. Based on its natural rarity, coupled with ongoing habitat degradation, A. gramineum was listed as a species of special concern in 2013. 

  Description

Alisma gramineum is a short-lived perennial aquatic plant that roots in shallow water. The stem is submerged or occasionally emergent and can reach a length of about 50 cm (20 in.). The submerged leaves are ribbon-like or grass-like (hence the name “gramineum”), up to 100 cm (40 in.) long, and 2 cm (0.75 in.) wide. The emergent leaves (when present) have a petiole with a linear lanceolate or narrowly elliptic blade, 2-6 cm (0.75-2.25 in.) long, and less than 2 cm (0.75 in.) wide. The flowers are arranged in a branched inflorescence; they remain closed when underwater and open when above the water surface. Open flowers are purplish white, 4-8 mm (0.20-0.30 in.) across, and consist of 3 petals and 3 sepals. The fruits are dry and brown. The achenes (seeds) are arranged in a ring, 3-6 mm (0.12-0.24 in.) in diameter, on a flat receptacle. Compared to the two other species of Alisma in Minnesota, Alisma gramineum is more aquatic and has narrower leaves (Hendricks 1957; Haynes and Hellquist 2000).

  Habitat

In the lake country of Minnesota (Laurentian Mixed Forest), the primary habitat of A. gramineum appears to be shallow water (less than 1 m [40 in.] deep) over a sandy substrate in bays of large and wind-swept lakes. Water chemistry analysis at one site revealed total alkalinity to be 138 ppm, with a pH of 8.6. This habitat type is usually very sparsely vegetated. When A. gramineum is found in an area, it may be the only plant species present. In the prairie region of Minnesota (Prairie Parkland), the habitats of A. gramineum are less well known but appear to include shallow nutrient-rich lakes or ponds and associated wetlands.

  Biology / Life History

When the flowers of A. gramineum develop below the surface of the water, they remain closed and are self-pollinated. Whereas, when the flowers rise above the water surface, they open and attract insect pollinators. Seed dispersal within a lake basin, and between interconnected basins, is likely accomplished by water currents; though movement from one isolated basin to another is likely accomplished by water birds, whether transported in the gut or as unintentional hitchhikers in their feathers is unknown.

Alisma gramineum does not spread by underground stems or stem fragments; it reproduces only by seed. Seeds apparently do not germinate the season they are produced because they require a cold-stratification period, which can be accomplished either underwater or above water while stranded on the lakeshore. Some dormant seeds apparently enter a multi-year seed bank. Germination can occur underwater or in moist soil above the water level.

Although primarily a submerged plant, A. gramineum apparently also survives well if stranded above the waterline when water levels recede, and this may enhance seed production (Hudon 2004). Since this species relies on a regular or periodic influx of seeds, the annual cycle of changing water levels may be essential to the maintenance of populations. It has been postulated that compared with other species in this genus, A. gramineum is more dependent on natural regimes of water level fluctuation and is most susceptible to artificial changes (Moravcová et al. 2001).

  Conservation / Management

The primary threat facing A. gramineum in Minnesota is loss or degradation of habitat, primarily through declining water quality (pollution), non-compatible recreational activity (uprooting by motor boats, etc.), and destructive shoreline management (use of weed-rollers, increased sedimentation, herbicide run-off, etc.). In virtually all cases, any management that maintains the natural diversity and abundance of aquatic and shoreline vegetation in a lake will benefit Alisma gramineum.

  Best Time to Search

The best time to search for A. gramineum, is when flowers or fruit are present, usually between about July 17 and September 17.

  Authors/Revisions

Welby R. Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Haynes, R .R., and C. B. Hellquist. 2000. Alismataceae. Pages 7-25 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 22. Oxford University Press, New York, New York.

Hendricks, A. J. 1957. A revision of the genus Alisma (Dill.) L. The American Midland Naturalist 58 (2):470-493.

Hudon, C. 2004. Shift in wetland composition and biomass following low-level episodes in the St. Lawrence River: looking into the future. Canadian Journal of Fisheries and Aquatic Sciences 61(4): 603-617.

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.

Moravcova, L., P. Zakravsky, and Z. Hroudova. 2001. Germination and seedling establishment in Alisma gramineum, A. plantago-aquatica and A. lanceolatum under different environmental conditions. Folia Geobotanica 36(2):131-146.

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