5. L. gíbba, L. Fronds obovate-elliptic to nearly orbicular, almost hemispherical, soon separating; bract sac-like.—Mo. (?) to Ariz. and Calif.
3. WÓLFFIA, Horkel.
Flowers central, bursting through the upper surface of the globular (or in some foreign ones flat) and loosely cellular frond, only 2; one consisting of a single stamen with a 1-celled 2-valved anther; the other of a globular ovary, tipped with a very short style and a depressed stigma. Ovule orthotropous, rather oblique in the cell. Utricle spherical. Albumen thin.—Fronds rootless, proliferous from a cleft or funnel-shaped opening at the base, the offspring soon detached; no rhaphides.—The simplest and smallest of flowering plants, from ¼–{2/3}´´ long (an African and Cuban species much larger), floating as little grains on the water. (Named for John Fred. Wolff, who wrote on Lemna in 1801.)
1. W. Columbiàna, Karsten. Globose or globular, {1/3}–{2/3}´´ long, very loosely cellular, light green all over, not dotted; stomata 1–6; the opening at the base circular and with a thin border.—Floating rather beneath the surface of stagnant waters, Conn. to N. J., west to Minn. and La.
2. W. Brasiliénsis, Weddell. Oblong, smaller and more densely cellular, flattish and deep green with many stomata above, tumid and pale below, brown-dotted all over, anterior edge sharp, opening at base circular.—Growing with the last, but floating on the surface.
Order 125. ALISMÀCEÆ. (Water-Plantain Family.)
Marsh herbs, with scape-like stems, sheathing leaves, and perfect or monœcious or diœcious flowers; perianth of 3 herbaceous persistent sepals and as many (often conspicuous) white deciduous petals, which are imbricate or involute in bud; stamens 6 or more, included; ovaries numerous, distinct, 1-celled and mostly 1-ovuled, becoming achenes in fruit (in our genera); seeds erect; campylotropous.—Roots fibrous; leaves radical, petiolate and strongly nerved with transverse veinlets, the earlier sometimes without blade; flowers long-pedicellate, mostly verticillate, in a loose raceme or panicle, with lanceolate scarious bracts slightly connate at base.
1. Alisma. Flowers perfect, usually 6-androus. Carpels flattened, in one whorl.
2. Sagittaria. Flowers mostly unisexual. Stamens rarely few. Carpels flattened, in dense heads, winged.
3. Echinodorus. Flowers perfect. Stamens 6 or more. Carpels capitate, turgid and ribbed, often beaked.