Grass Alisma (Alisma gramineum) Potential Occurrence: Unlikely To Occur Status

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Lilioposida (Grasses, Lillies, Orchids): Alismataceae

Grass Alisma (Alisma gramineum)

Potential Occurrence: Unlikely To Occur


Federal: None

State: None

CNPS: 2.2

Photo : Louis M. Landry

Photos : R.V. Lansdown

ther: None

Species Description: Grass Alisma is a monocot with linear to narrowly lancolate leaves (CNPS 2010; Hickman 1996). The inflorescence is scapose and umble or panicle like with a smooth peduncle and bisexual flowers with flat receptacles, white to pink petals and more or less curved styles of the many pistils. The fruit is a strongly compressed achene with lateral walls generally thin and opaque. (Hickman 1996)

Nomenclature: Alisma gramineum Lej. Alismataceae (USDA 2010)

Synonyms: Alisma geyeri Torr. (Regents of the University of California 2010)

Distribution: This species is known largely from the Modoc Plateau in northeastern California, but there are several documented occurrences in Mendocino County north of Willits in elevations between 390 to 1800 m (Calflora 2010; CNPS 2010; Hickman 1996).

Life History & Threats: Grass Alisma is a perennial rhizomatous aquatic herb that behaves like an annual (ARKive 2010; CNPS 2010). When the flowers grow underwater they are cleistogamous allowing for self pollination (eFloras 2008). In contrast, tresestrial plants are chastagomus, allowing for open pollination (eFloras 2008). The germination of seed may rely on freezing or the distubance of mud after the seed falls (ARKive 2010). The greatest threat to this species is road construction (CNPS 2010). In addition the algal growth associated with eutrophication of water bodies and competition from other marginal and aquatic species is contributing to the decline of this species (UK Biodiversity Action Plan 2010).

Habitat & Habitat Associations:

Habitat: Freshwater or brackish lakes and marshes or on muddy shores of lakes and marshes where the dominant vegetation is emergent, suffrutescent herbs adapted to seasonally or permanently saturated soils (CNPS 2010; eFloras 2008; Smith and Wheeler 1992). It can also be found in shallow waters or mud around the margins of rivers, ponds and ditches (ARKive 2010).

Elevation: 390 to 1800 m (CNPS 2010). (The Study Area ranges from 230 to 710 m).

Geology and Soils: muddy areas (CNPS 2010)

Species Associations: cannot tolerate competition from other plants (ARKive 2010)

Other Special Habitat Features: open habitats, nutrient rich conditions (ARKive 2010)

Conceptual Basis for GIS Model Development: Potential habitat in the Study Area was mapped as areas with:

  • above 360 m (includes a 30 m buffer on known elevational occurrences of this species)

  • edges of ponds and drainages. (Note that many ponds in the are below 360 m and do not show up as potential habitat on the map).

Springs and seeps are common throughout the Study Area but are not available in a GIS database. Seeps typically occur in open grassy areas and are dominated by rushes (Juncus spp.), sedge (Cyperus eragrostis), mint (Menthe puleglum), bracken ferns (Pteridium aquilium). Springs, sites with surface water, occur in many habitat types and vary in species composition.

Potential Occurrence in the Galbreath Wildlands Preserve:

Habitat: Habitat for this species is seasonally or perennially saturated soils associated with surface water in open areas above 360 m. The GIS map indicates that these types of habitats may occur at three ponds along the southwestern border of the Preserve and in the upper reaches of drainages. This distribution shown is an overestimate of potential habitat: at this elevation, the drainages are seasonal and rarely wet enough to provide habitat for this species. The distribution also underestimates potential habitat since springs and seeps are common throughout the Preserve, but are not mapped.

Habitat quality for this species at ponds, seeps and springs is poor to moderate. The three ponds, two natural and one agricultural, are shaded by surrounding coniferous and broadleaf upland forest types. Seeps and springs typically occur in open grassy areas and are dominated by rushes (Juncus spp.), sedge (Cyperus eragrostis), mint (Menthe puleglum), bracken ferns (Pteridium aquilium). These sites are inappropriate for this species, which is intolerant of competition and requires open habitats. The most likely areas for this species to occur could be pig wallows. Pig wallows that are in open areas and, if only sporadically used, could provide the open, muddy habitat needed by Grass Alisma.

Nearest Occurrence:

Documented Occurrences in the Galbreath Wildlands Preserve: Previous species list for the Galbreath Wildlands Preserve did not document this species (SSU Field Station and Nature Preserves 2010).

Nearest Occurrence to the Galbreath Wildlands Preserve: Grass Alisma is known from 8 occurrences in Mendocino County (Calflora 2010), all north of the Preserve. The nearest documented occurrence of is 40 miles north of the Preserve in the Noyo River watershed (Calflora 2010), a distance over 3 times further than the greatest distance documented among reported occurrences in Mendocino County.

Summary: We anticipate that this species is “Unlikely to Occur” in the Galbreath Wildlands Preserve due to the poor habitat quality and low habitat abundance in the Preserve, and the remoteness of other documented occurrences from the Preserve.


ARKive. 2010. . Accessed 2010 Jun 24.

Calflora. 2010. Information on California plants for education, research and conservation.. Accessed 2010 Jun 19.

California Native Plant Society (CNPS). 2010. Inventory of Rare and Endangered Plants. Online edition, v7-10b. . Accessed 2010 Jun 19.

eFloras 2008. Flora of North America. . Accessed 2010 Jun 27.

Hickman JC editor. 1996. The Jepson Manual Higher Plants of California. 3rded. London: University of California Press, Ltd.1101 p.

Landry LM. 2010. Alisma gramineum. . Accessed 2010 Jun 27.

Landsdown RV. 2010. Ribbon-Leaved Water-Plantain (Alisma gramineum). . Accessed 2010 Oct 4.

Regents of the University of California. 2010. The Jepson Online Interchange California Floristics. . Accessed 2010 Oct 4.

Smith GL, Wheeler CR. 1992. A flora of the Vascular Plants of Mendocino County, California. San Francisco: University of San Francisco. 63 p.

SSU Field Stations and Nature Preserves. 2010. Galbreath Wildlands Preserve Vascular Plant List. . Accessed 2010 Jun.

UK Biodiversity Action Plan. 2010. Species Action Plant. Ribbon-leaved Water-plantain (Alisma gramineum). . Accessed 2010 Jun 27.

United States Department of Agriculture (USDA). 2010. PLANTS Profile. . Accessed 2010 Oct 4.

Species Account Description: Linden Schneider

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