14 Flora of the Palouse Region 



Carpels in a ring upon a small flat receptacle. 22. alisma. 



Carpels crowded in many series upon a large convex receptacle. 



23. SAGITTARIA. 



22. ALISMA. 



Perennial or rarely animal herbs with erect or floating leaves: 

 inflorescence a panicle or umbel-like panicle: flowers perfect, 

 small, numerous, on unequal 3-bracted pedicels: petals small: 

 stamens 6 or 9: ovaries few or many, borne in one or several 

 whorls on a small flat receptacle. 



A. plant-ago L- Scapes stout, .3-1 m. tall: leaves all radical, erect or 

 floating; the petioles usually long; the blades ovate or oblong, acute, 

 rounded or subcordate at the base, 5-15 cm. long, 5-7-nerved: flowers in a 

 large panicle composed of 3-6 whorls of branches, these again branched once 

 or twice; flowers on pedicels 1-5 cm. long: petals white, hardly exceeding 

 the sepals: akenes obliquely obovate, compressed, arranged in a circle on the 

 receptacle. Common in ponds and wet places. 



23. SAGITTARIA. 



Perennial aquatic or marshherbs with basal long-petioled leaves: 

 flowers monoecious or dioecious, borne near the summits of the 

 scapes in whorls of 3, the staminate usually uppermost: petals 

 usually conspicuous: stamens usually numerous: ovaries numer- 

 ous, crowded in globose heads. 



S. arifolia Nutt. Terrestrial or aquatic, 10-50 cm. tall: petioles stout, 

 ascending, 10-30 cm. long; blades 6-18 cm. long, sagittate, acute, the basal 

 lobes diverging and usually much smaller than the terminal one: sepals be- 

 coming reflexed: petals white: fruiting head globose, 8-15 mm. in diameter: 

 akenes obovate- cuneate, much flattened, with a minute erect beak. Com- 

 mon on the margins of ponds and streams. 



Familv 12. GRAMINEAE. 



Annual or perennial herbs, rarely shrubs or trees: stems (culms) 

 generally hollow, nodes closed: leaves sheathing, the sheaths usu- 

 ally split to the base on the side opposite the blade; a scarious or 

 cartilaginous ring (the ligule ) usually borne at the opening of the 

 sheath: inflorescence a spike, a raceme or a panicle, consisting of 

 spikelets composed of 2 — many 2 -ranked imbricated bracts 

 (glumes); the lowest two (empty glumes) without flowers or 

 rarely wanting; one or more of the upper (flowering 

 glume) containing in its axil a flower, which is usually enclosed 

 by a bract-like, generally 2-keeled, awnless organ (palet) opposite 

 the glume and with its back toward the axis (rachilla) of the spike- 

 let; upper flowering glume sometimes bearing a hard protuber- 

 ance (callus) at the base: flowers perfect or sometimes monoecious 



