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..
Slender, widely branched aquatics with capillary stems, slender alternate 1-nerved leaves tapering to an acuminate apex, and with membranous sheaths. Flowers on a capillary spadix-like peduncle, naked, consisting of 2 sessile anthers, each with 2 large separate sacs attached by their backs to the peduncle, having between them several pistillate flowers in 2 sets on opposite sides of the rachis, the whole cluster at first enclosed in the sheathing base of the leaf. Stigmas sessile, peltate. Fruit a small, obliquely pointed drupe, several in each cluster and pedicelled; embryo oval, the cotyledonary end inflexed, and both that and the hypocotyl immersed. [Name in honor of Heinrich Bernhard Rupp, a German botanist.]
In the development, the staminate flowers drop off, the peduncle elongates, bearing the pistillate flowers in 2 clusters; after fertilization it coils up and the fruit is drawn below the water.
Three or four species, occurring in salt and brackish waters all over the world. Type species: Ruppia maritima L. The following are the only ones known to occur in North America.
Sheaths 3"-4" long; drupes about 1" long.
Sheaths 1/2'- 1 1/2' long; drupes 1 1/2"-2 " long.
Stems often whitish, 2°-3° long, the in-ternodes irregular, naked, I'-3' long. Leaves 1'-3' long,:1/4" or less wide; sheaths 3"-4" long, with a short free tip; peduncles in fruit sometimes 1° long; pedicels 4-6 in a cluster, 1/2'-l 1/2' long; drupes with a dark hard shell, ovoid, about 1" long, often oblique or gibbous at the base, pointed with the long style, but varying much in shape; forms with very short peduncles and pedicels, and with broad, strongly marked sheaths occur.
Common along the coasts and in saline districts in the interior. Old World and South America. Tassel-grass. July-Aug.
25: 138. Sept. 1890. Ruppia lacustris Macoun, Cat. Can. PI. 5: 372.
Stems stouter, 1°-2° long, the branching fan-like. Leaves 3'-8' long, their large sheaths 1/2'-1 1/2' long; branches and leaves often thickly clustered at the nodes, the sheaths overlapping each other; drupes larger, 1 1/2"-2" long, ovoid or pyriform, borne on pedicels about 1' long, the peduncles bright red when fresh and sometimes nearly 2° in length.
In saline ponds, Nebraska to British Columbia.