NAIADACE^E. (PONDWEED FAMILY.) 861 



ORDER 85. ALJSUIACEjE. (WATER-PLANTAIN FAMILY.) 



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

 monoecious flowers not on a spadix, furnished with both calyx and 

 corolla; sepals and petals each 3, distinct; ovaries numerous, distinct, 

 becoming akenes in fruit. Roots fibrous ; leaves radical, petiolate, 

 strongly nerved with transverse veinlets, the earlier sometimes without 

 blade; flowers in a loose raceme or panicle. 



1. Alisma. Flowers perfect. Carpels verticillate, obovate-oblong, flattened. 



2. Sag! tt aria. Flowers monoecious or dioecious. Carpels capitate, flattened and mem- 



branously winged. 



1. A L IS MA, L. WATER-PLANTAIN. 



Petals small. Stamens 6, rarely more. Ovaries on a disk-like receptacle. 

 Akenes in a crowded whorl, somewhat channelled on the back, obtuse. 

 Herbs in shallow water or mud, with small flowers in a verticillately branched 

 panicle. 



1. A. PlantagO, L., var. Americanum, Gray. Leaves long-petioled, 

 ovate, oblong, or lanceolate, pointed, mostly rounded or heart-shaped at the 

 base, 3 to 9-nerved : carpels obliquely obovate, forming an obtusely triangular 

 whorl in fruit. From the base of the mountains eastward across the conti- 

 nent ; also from California to Washington Territory. 



2. SAGITTABIA, L. ARROW-HEAD. 



Staminate flowers above. Petals usually conspicuous. Stamens numerous, 

 rarely few. Ovaries crowded in globose heads. Akenes abruptly beaked by 

 the very short style. Stoloniferous herbs with milky juice, broadly sheathing 

 leaves often without a blade, and mostly simple stems bearing one to few whorls 

 of flowers usually in threes. 



1. S. variabilis, Engelm. Rootstock tuberiferous : scape to 2 feet 

 high or more, angled : leaves very variable, ovate-sagittate, or more or less 

 narrowed, or even linear, acute, the similar lobes more or less divergent, acu- 

 minate: petals white, rounded, exceeding the sepals: fruiting heads nearly 

 half an inch in diameter : akenes obovate, with a conspicuous acute horizontal 

 beak at the upper angle. From the mountains eastward across the conti- 

 nent ; also from Nevada and California to British Columbia. 



ORDER 86. NAIADACE^E. (PONDWEED FAMILY.) 



Marsh or mostly immersed aquatic herbs, with stems jointed and 

 leafy (naked and scape-like in Triglochin), leaves sheathing at base or 

 stipulate, and flowers perfect or unisexual, often spathaceous, with or 

 without perianth ; ovaries 1 -celled, 1-ovuled. 



