Vallisneria americana Michx., Hydrocharitaceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Other Latin names:  Vallisneria gigantea Graebn.

Common name(s): [more details]

English: American eelgrass, eel grass, flumine Mississippi, tape grass, water celery, wild celery

Habit:  aquatic herb

Description:  "Submerged aquatic perennial.  Several ribbon-like leaves of varying lengths borne on short vertical stems, the latter arising as short-stemmed clusters from nodes of horizontal rhizomes.  Numerous, fibrous, unbranched roots borne about the bases of the vertical shoots.  Longer leaves commonly with their tips more or less floating on the water surface.  Leaves with scarcely perceptible midrib, to transmitted light appearing very fine lined and with irregular darker green partial cross lines.  Leaf margins bearing minute staggered teeth.  Plants dioecious.  Male inflorescence short stalked in a closed spathe within which some 200 tightly packed slender-pedicillate staminate flowers are borne.  Staminate flowers tiny, with 3 very thin, completely transparent, spoonlike sepals, 2 of equal size, the third, somewhat smaller.  Above and opposite the smaller sepal is the smaller, tongue-like, completely transparent petal.  Above and between the 2 larger sepals is a single, transparent, much reduced sterile stamen.  Fertile stamens 2, filaments fused at the base.  Pistillate flowers borne singly from the leaf axils, each at the end of a peduncle as long as or longer than the longest leaves.  Bud enclosed in a transparent spathaceous envelope which tightly invests it.  As the flower becomes fully developed the spathe splits at the summit and by elongation of the floral tube the flower extends beyond the spathe, the latter ultimately appearing like a bract at the base of the very much elongated fruit.  At anthesis, the open summit of the female flower is at the water surface.  Subsequent to pollination (and presumably fertilization), the flower stalk coils markedly, thus pulling the developing fruit well beneath the surface of the water where it matures.  Floral tube long-cylindrical, surmounted by three spreading, ovate-oblong, thickish persistent sepals about 3-4 mm long.  Alternate with each sepal, just above the sinus between two sepals, is a tiny rudimentary petal which soon disintegrates.  Style short, stigmas 3, each cleft to the base.  Fruit 1-locular, bearing 250-500 seeds, or thereabouts, throughout its length.  Mature capsule dehisces longitudinally by one valve and the seeds are shed in a copious mass of gelatinous material"  (Godfry & Wooten, 1979; p. 74).

"Scapes: staminate scapes 30-50 mm, submersed; pistillate scapes elongate, projecting flowers to surface. Leaves 10-110, 0.3-1.5 cm; leaf blade 3-zoned longitudinally, margins entire to serrate. Flowers: staminate flowers 1-1.5 mm wide; stamens 2, filaments basally connate; pistillate flowers solitary, rarely in umbel-like clusters"  (Flora of North America online).

"Leaf blades 6 inches to 6 feet x 0.25-1.2 inches, margins entire to finely toothed, staminate flowers numerous per spathe, ca. 0.05 inches in diameter, stamens upright, filaments partly or wholly united; pistillate flowers solitary (rarely in umbels), sepals 0.1-0.25 inches long, sterile stamens conspicuous, ±fused to style bases, stigmas not fringed"  (Staples & Herbst, 2005; p. 667).

Habitat/ecology:  "In both quiet and swiftly flowing waters"  (Godfry & Wooten, 1979; p. 74).

Propagation:  Seed

Native range:  North America, West Indies; Central America; Asia (Flora of North America online).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced invasive	Staples, George W./Imada, Clyde T./Herbst, Derral R. (2003) (p. 13) Vouchers cited: T. Flynn 897 (BISH), T. Flynn 6196 (BISH)
State of Hawaii Hawaiian Islands	Maui Island	introduced invasive	Oppenheimer, Hank (2008) (p. 29) West Maui. Voucher cited: Oppenheimer & C. Brosius H120514 (BISH, PTBG)
State of Hawaii Hawaiian Islands	O‘ahu Island		Bishop Museum (U.S.A. Hawaii. Honolulu.) (1984) (voucher ID: BISH 471826) Taxon name on voucher: Vallisneria americana Michx.
Papua New Guinea Papua New Guinea (eastern New Guinea Island)	Papua New Guinea (eastern New Guinea Island)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Philippines Philippine Islands	Philippine Islands	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Philippines Philippine Islands	Philippine Islands	native	Merrill, Elmer D. (1925) (p. 26) As Vallisneria gigantea Graebn. In lakes and slow streams at low altitudes.

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
British Columbia (province of Canada) Province of British Columbia	Canada (British Columbia)	native	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
Cambodia Cambodia	Cambodia (Kingdom of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	Guatemala (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	Honduras (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
China China	China (People's Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Japan Japan	Japan	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
North Korea North Korea	North Korea (Democratic People's Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
South Korea South Korea	South Korea (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Mexico Mexico	Mexico (United Mexican States)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
United States (west coast) United States (west coast states)	USA (Oregon)	native	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (west coast) United States (west coast states)	USA (California)	native	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (west coast) United States (west coast states)	USA (Washington)	native	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
Vietnam Vietnam	Vietnam (Socialist Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)

Also reported from
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Canada Canada	Canada	native	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (continental except west coast) United States (other states)	United States (other states)	native	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (continental except west coast) United States (other states)	USA (Florida)	native	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)

Comments:  "Two distinct phenotypes are represented among Hawaiian plants: a diminutive plant with leaves only 15-40 cm long and 6-10 mm wide; and a robust plant with leaves exceeding 1 m in length and 3 cm wide.  Both phenotypes are sold as aquatic ornamentals; the latter is also eaten as a potherb and is sold for that purpose in local produce markets" (Staples, Imada & Herbst, 2003; p. 13).

Control:  If you know of control methods for Vallisneria americana, please let us know.