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 aquatic or bog herbs, mostly with tuber-bearing or nodose rootstocks, fibrous roots, basal long petioled nerved leaves, the nerves connected by numerous veinlets, and erect, decumbent or floating scapes, or the leaves reduced to bladeless phyllodia (figs. 241, 242). Flowers monoecious or dioecious, borne near the summits of the scapes in verticils of 3's, pedicelled, the staminate usually uppermost. Verticils 3-bracted. Calyx of 3 persistent sepals, those of the pistillate flowers reflexed or spreading in our species. Petals 3, white, deciduous. Stamens usually numerous, inserted on the convex receptacle; anthers 2-celled, dehiscent by lateral slits; staminate flowers sometimes with imperfect ovaries. Pistillate flowers with numerous distinct ovaries, sometimes with imperfect stamens; ovule solitary; stigmas small, persistent. Achenes numerous, densely aggregated in globose or subglobose heads, compressed. Seed erect, curved; embryo horseshoe-shaped. [Latin, referring to the arrow-shaped leaves of some species, known generally as Arrow-head or Arrow-leaf.]
About 40 species, natives of temperate and tropical regions. Besides the following, some 18 others occur in southern and western North America. Type species: Sagittaria sagittifolia L.
Fertile pedicels slender, ascending, not reflexed in fruit.
Leaf-blades sagittate or hastate.
Basal lobes one-fourth to one-half the length of the blade.
Beak of the achene erect.
Achene long-beaked, the beak mostly 1/2 the length of the body or more.
Achene obovate or orbicular-obovate, usually with 1 facial wing.
1. S. longirostra.
Achene cuneate, usually with 2 prominent facial wings.
Achene short-beaked, the beak mostly 1/4 the length of the body or less.
Achene with thick nearly equal wings, the blunt beak over the inner edge of the
Achene with thin unequal wings, the sharp beak over the outer edge of the
Beak of the achene horizontal.
Achene with nearly even faces: bracts and pedicels glabrous.
Achene faces prominently winged; bracts and pedicels pubescent.
6. S. pubescens.
Basal lobes two-thirds to three-fourths the length of the blade.
Leaves entire, or rarely hastate or cordate.
Filaments tapering upward; leaves seemingly pinnately veined.
Filaments glabrous; bracts connate.
Filaments cobwebby-pubescent; bracts mostly distinct.
Filaments abruptly dilated, pubescent; veins distinct to the base.
Fruiting heads sessile or very nearly so.
Both staminate and pistillate flowers pedicelled.
Leaves with terete or 3-sided blades, often imperfectly developed.
Achene with thick merely uneven facial wings or ridges, the beak erect.
Achene with thin crested facial wings, the beak oblique.
Leaves with flat blades.
Filaments suborbicular; anthers longer than the filaments.
Filaments oblong; anthers about as long as the filaments.
Fertile pedicels stout, reflexed in fruit; filaments dilated.
Filaments pubescent: leaf-blades ovate or ovate-elliptic.
Filaments glabrous; leaves linear-lanceolate or reduced to phyllodia.
Filaments about as long as the anthers; achene with 3 undulate or slightly toothed crests.
Filaments much longer than the anthers; achene with 5-7 tuberculate or prominently