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| ## Western mannagrass {#western-mannagrass .Title-Header}             |
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| *Glyceria occidentalis* (Piper) J.C. Nels.                            |
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| Plant Symbol = GLOC                                                   |
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Contributed by: USDA NRCS Plant Materials Center, Corvallis, Oregon

##### Alternate Names {#alternate-names .Header-3}

##### Other names are Northwestern mannagrass, tall mannagrass, and waxy mannagrass.

##### Uses {#uses .Header-3}

Western mannagrass is a native species important for restoration of
freshwater marshes, vernal pools, and depressions within wetland
prairies. The species rapid growth, underground stems, and floating
leaves aid in reducing erosion along the edges of streams and lakes
where it naturally occurs. In the Pacific Northwest, this grass is
recommended for use in stormwater management, including detention ponds
and biofiltration swales that are wet year round. The foliage and seeds
provide food and cover for waterfowl, small seed-eating birds, muskrats,
and other small mammals. Western mannagrass may be useful in seed
mixtures aimed at increasing plant diversity while helping deter the
invasion of reed canarygrass (*Phalaris arundinacea*). The seed can be
dried and ground into flour and was apparently eaten by Native
Americans.

##### Status {#status .Header-3}

Please consult the PLANTS Web site and your State Department of Natural
Resources for this plant's current status (e.g. threatened or endangered
species, state noxious status, and wetland indicator
values).![](media/image3.jpeg){width="2.841666666666667in"
height="4.002777777777778in"}

##### Description and Adaptation {#description-and-adaptation .Header-3}

Western mannagrass is a short-lived, cool season perennial grass with
flaccid stems (culms) that reach a height of 70 to 150 cm. The form is
moderately coarse textured, clumpy, and upright to nearly flat:
spreading from rhizomes or decumbent (low lying) stems that root at the
nodes (joints). When submerged in spring, this species produces floating
stems and leaves, but flowering is reduced. Leaf blades are ribbon-like,
4 to 13 mm wide, and 15 to 30 cm long. Flowerheads (panicles) are narrow
and 15 to 40 cm long, with appressed branches and long cylindrical
spikelets (the groupings of individual florets or flowers). The
flowering period is long, from May to September. Western mannagrass
occurs from British Columbia south to California and east to Idaho and
Nevada at elevations below 4000 feet.

*Key to identification:* Western mannagrass is easily confused with
northern mannagrass (*Glyceria borealis*) and slender spiked mannagrass
(*Glyceria leptostachya*) which are found in similar aquatic habitats.
Western mannagrass has larger florets (individual flowers) and the seed
is three times larger compared to the other two. A botanical key, scale,
and hand lens are needed for proper identification.

*Relative abundance in the wild:* This species is widely occurring and
common in the Pacific Northwest at low elevations, especially along
streams and in wet meadow depressions. Despite the long flowering
period, seed collection is laborious because retention is poor: the seed
drops (shatters) very easily when green and not fully mature. However,
additional seed may be held within the lower leaf sheath and can be
removed by threshing.

*Adaptation:* This species is easy to establish and grow on adapted
sites. It can volunteer readily.

Western mannagrass grows naturally in vernal pools, wet depressions,
marshes, and ditch bottoms, as well as along the shores of lakes,
streams, and ponds. While found in full sun, it occasionally occurs in
partial shade as well. Soils include poorly drained sands, loams, and
clays with acid, neutral or slightly alkaline pH. This species can grow
in permanent standing or slow moving water at least 30 cm deep. It is
intolerant of drought and is not found on saline sites. Soil fertility
requirements are moderate.

![](media/image4.jpeg){width="1.7194444444444446in"
height="2.188888888888889in"}

##### Establishment {#establishment .Header-3}

The seed has no physiological dormancy and germinates readily without
treatment in less than three weeks. The species can be broadcast on the
surface of mud or muck in the fall or spring. Moist soil is adequate for
germination, but if the site is inundated prior to germination, the seed
must be secured in place with a thin mulch or mat to prevent it from
floating or washing away. The hull detaches readily but can be left
intact. There are approximately 215,000 to 360,000 seeds/lb (+/- 20%)
with and without hulls, respectively. A seeding rate of 1 lb pure live
seed per acre will result in about 5 to

8 live seeds per square foot. Actual seeding rates will depend on
methods, objectives, and site conditions. Western mannagrass is easily
propagated by division or as container stock sown from seed and
maintained in shallow standing water.

##### Management {#management .Header-3}

There is a lack of information about the management of western
mannagrass. It can be grown and maintained under continuously moist,
saturated, or seasonally to permanently flooded conditions. Regeneration
and spread is favored by wet open areas and disturbance. Water
impoundments or other controlled wetlands should not be allowed to dry
out, especially if viable seed has not yet formed.

##### Environmental Concerns {#environmental-concerns .Header-3}

Seed is difficult to collect in the wild. Western mannagrass is a
serious weed in low lying, poorly drained fields of introduced grasses
grown for seed in Oregon. Some strains may be herbicide resistant.
Riparian wetland and stream restoration projects should consider
substituting other native grasses if ryegrass (*Lolium* spp.) seed
fields are downstream. Consult with your local Extension Service agent,
weed control handbook, or other experts for advice.

##### Cultivars, Improved, and Selected Materials (and area of origin) {#cultivars-improved-and-selected-materials-and-area-of-origin .Header-3}

Seeds, plugs, or containers are usually available, but seed is often
expensive.

##### Prepared By:  {#prepared-by .Header-3}

*Dale Darris*, USDA NRCS Plant Materials Center, Corvallis, Oregon.

##### Species Coordinator:  {#species-coordinator .Header-3}

*Dale Darris*, USDA NRCS Plant Materials Center, Corvallis, Oregon.

##### Edited: 21mar2006 jsp, 17sept2008 dcd; 080919 jsp {#edited-21mar2006-jsp-17sept2008-dcd-080919-jsp .Header-4}

For more information about this and other plants, please contact your
local NRCS field office or Conservation District, and visit the PLANTS
Web site\<[http://plants.usda.gov](http://plants.usda.gov/)\> or the
Plant Materials Program Web site
\<[http://Plant-Materials.nrcs.usda.gov](http://Plant-Materials.nrcs.usda.gov/)\>

*The U.S. Department of Agriculture (USDA) prohibits discrimination in
all its programs and activities on the basis of race, color, national
origin, sex, religion, age, disability, political beliefs, sexual
orientation, and marital or family status. (Not all prohibited bases
apply to all programs.) Persons with disabilities who require
alternative means for communication of program information (Braille,
large print, audiotape, etc.) should contact USDA\'s [TARGET
Center](http://www.usda.gov/oo/target.htm) at 202-720-2600 (voice and
TDD).*![](media/image5.jpeg){width="2.8in"
height="1.8854166666666667in"}

*To file a complaint of discrimination write USDA, Director, Office of
Civil Rights, Room 326-W, Whitten Building, 14th and Independence
Avenue, SW, Washington, DC 20250-9410 or call 202-720-5964 (voice or
TDD). USDA is an equal opportunity provider and employer.*

*Read about [Civil Rights at the Natural Resources Conservation
Service](http://www.nrcs.usda.gov/about/civilrights/).*