ALISMACE^E. ( WATER- PLANTAIN FAMILY.) 553 



pous, ovate or oval, obtuse, with scarcely apiculate operculum. N. Y. and N. J., 

 west to Mich, and Wise. Var. TRINERVIS, Austin, has larger, distinctly 3- 

 nerved fronds, and an unequally cordate seed. 



4. L. minor, L. Fronds round- to elliptic-obovate (l-2j"in diameter), 

 rather thick, very obscurely 3-nerved ; spathe sac-like ; utricle short-urn-shaped, 

 tipped with a short style ; seed oblong-obovate, amphitropous, with prominent 

 rounded operculum. Stagnant waters, throughout N. Am. (Eu.) 



* # Ovules 2-7, anatropous ; fronds very thick and spongy , flat above, very 

 obscurely 5-nerved (1^-3" long). 



5. L. gibba, L. Fronds obovate-elliptic to nearly orbicular, almost hemi- 

 spherical, soon separating; bract sac-like. Mo. (?) to Ariz, and Calif. 



3. WOLFFIA, 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 root- 

 less, 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 i-f" 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. Columbiana, Karsten. Globose or globular, J-f" 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 sur- 

 face of stagnant waters, Conn, to N. J., west to Minn, and La. 



2. W. Brasiliensis, Weddell. Oblong, smaller and more densely cellu- 

 lar, 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. ALJSMACEJE. (WATER-PLANTAIN FAMILY.) 



Marsh herbs, with scape-like stems, sheathing leaves, and perfect or monoe- 

 cious or dioecious 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, 

 \-celled and mostly l-ovuled, becoming achenes in fruit (in our genera) ; 

 seeds erect ; campylotropous. Roots fifcrous ; 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. ' 



8. Echinodorus. Flowers perfect. Stamens 6 or more. Carpels capitate, turgid and 

 ribbed, often beaked. 



