This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Perennial or rarely annual herbs with erect or floating leaves, the blades several-ribbed, the ribs connected by transverse veinlets, or seemingly pinnately veined. Scapes short or elongated. Inflorescence paniculate or umbellate-paniculate. Flowers small, numerous on unequal 3-bracteolate pedicels, the petals white or rose-tinted. Stamens 6 or 9, subperigynous. Ovaries few or many, borne in one whorl on a small flat receptacle, ripening into flattened achenes which are 2-3-ribbed on the curved back and 1-2-ribbed on the sides. [Greek, said to be in reference to the occurrence of the typical species in saline situations.l
About 10 species, widely distributed in temperate and tropical regions. Only the following are known to occur in North America. Type species i Alisma Plotttago-aquatica L.
Achenes longer than wide, grooved on the back, the inner edges not meeting in the whorl; peduncles and pedicels straight, ascending.
Petals slightly longer than the sepals; corolla 1 1/2"-21/4" wide.
Petals much longer than the sepals; corolla 5" - 6 1/2" wide.
Achenes as wide as long, ridged on the back, the inner edges meeting in the whorl; peduncles and
pedicels recurved in fruit.
* Text revised by Dr. John Kunkel Small.
Alisma subcordatum Raf. Med. Repos. N. Y. 5:
382. 1824. Alisma Plantago americanum R. & S. Syst. 7:
Plants erect; leaves oblong, elliptic, oval or ovate, or sometimes narrower, 1 1/4'-6' long, usually abruptly pointed at the apex, cuneate to truncate, or cordate at the base, the petioles often longer than the blades; scapes 1/3°-3° tall, solitary or several together, the branches and pedicels in whorls of 3-10, variable in length, usually slender, sometimes filiform; bracts lanceolate or linear, often acuminate; sepals broadly ovate to suborbicular, obtuse; petals white or pinkish, 1/2"-1" long; achene-heads 1 3/4"-2 1/4" broad, the achenes obliquely obovate, 3/4"-1" long, the beak small, ascending.
In shallow water and mud, Massachusetts to Minnesota, Florida and Texas. Differs from the Old World A. Plantago-aquatica L., with which it has been united. Great Thrumwort, Mad-dog-weed, Deil's-spoons. June-Sept.
Alisma brevipes Greene. Pittonia 4: 158. 1900.
Alisma superbum Lunell, Bull. Leeds Herb, 2: 5. 1908.
Plants similar to A. subcordatum in habit, but commonly larger; leaves oblong or oblong-lanceolate to ovate, 2'-7 1/2' long, acute, sometimes abruptly pointed at the apex, rounded, truncate or subcordate at the base or sometimes gradually narrowed to the petiole which commonly exceeds the blade in length; scapes 30 tall or less, the branches and pedicels very numerous, except in small plants; bracts lanceolate or linear-lanceolate; sepals suborbicular or orbicular-ovate, mostly over 1 1/2" long; petals white, 2 1/2-3" long; achene-heads 2 1/2"-3 1/4" broad, the achenes obovate, 1 1/4"-1 1/2" long.
In swamps and streams, Nova Scotia to Ontario, British Columbia, North Dakota and California. July-Sept.
Alisma arcuatum Lunell, Bot. Gaz. 43: 210. 1907. Not Michalet. 1854.
Alisma Geyeri Torr. in Nicollet, Rep. Hydro-graph. Miss. Riv. 162. 1843.
Plants diffuse; leaves oblong, elliptic, oblong-lanceolate or ovate-lanceolate, or rarely linear, 2'-3 1/2' long, acute or slightly acuminate at the apex, narrowed at the base, the petioles usually longer than the blades; scapes mostly 1/3°-1 3/4° long, more or less diffusely spreading, the branches and pedicels relatively stout; bracts lanceolate; sepals orbicular-ovate, about 1 1/4" long; petals pink, 1"-2" long; achene-heads 2 1/4"-2I" broad, the achenes suborbicular, about 1" in diameter, the beak erect or nearly so.
In mud and shallow water, New York to North Dakota, Oregon and Nevada. July-Sept.