WATER-WEED FAMILY 29 



1. PHILOTRIA Raf. WATER-WEED. 



Submerged water plants with elongated branched stems, often rooting at the 

 nodes, dioecious or polygamo-dioecious. Leaves opposite or whorled, sessile, 

 pellucid, 1-nerved. Spathe 2-cleft at the apex, that of the staminate plant oval 

 or obovate, sessile, stipitate, in the pistillate plant lanceolate and sessile. 

 Sepals and petals 3 or the latter lacking. Stamens in the staminate flowers 

 usually 9, in two series, in the inner series 3; in the hermaphrodite usually only 3. 

 Fruit linear or lance-linear. [Elodea Michx.] 



Staminate flowers sessile, breaking off within the spathe; petals wanting. 



1. P. Planchonii. 



Staminate flowers on elongating pedicels, carrying them to the water surface; petals 

 present. 2. P. iowensis. 



1. P. Planchonii (Gasp.) Rydb. Dioecious water plant; stem slender, 

 1-10 dm. long; leaves in 3's or the lower opposite, oblong to linear, 7-15 mm. 

 long, 1-2 mm. wide, acutish; spathe of the staminate plant obovoid-clavate, 

 nearly 1 cm. long, on a stipe 5-10 mm. long; sepals elliptic, 5 mm. long; petals 

 lacking; spathe of the pistillate plant lance-linear, sessile; tube of the hypanthium 

 3-5 cm. long; sepals and petals linear, about 3 mm. long. Lakes and ponds: 

 Sask. Colo. Nev. Plain Submont. 



2. P. iowensis Wylie. Dioecious water plant; leaves lanceolate to oblong- 

 linear, 8-14 mm. long, 2-3.5 mm. wide; spathe of the staminate flowers obovate, 

 contracted to a narrow base; sepals oval, 4 mm. long; petals linear-lanceolate, 

 acuminate; spathe of the pistillate flowers linear-cylindric, 1-1.5 cm. long; 

 hypanthium 3-15 cm. long; sepals oval, 2 mm. long; petals obovate; staminodia 3. 

 Lakes: Iowa Colo. Plain. 



FAMILY 12. POACEAE. GRASS FAMILY. 



Annual or perennial herbs, or in warmer climates sometimes trees or 

 vines. Stems (culms) usually hollow except at the nodes. Leaves sheath- 

 ing at the base; the sheaths usually split on the side opposite the blades. 

 Inflorescence spicate, racemose or paniculate, consisting of spikelets com- 

 posed of usually 2-ranked bracts called glumes, the lower 1-4, usually 2, 

 empty, the remaining (lemma) enclosing a bract-like organ (the palet), and 

 inside this a flower, usually consisting of 3 stamens and 1 pistil. Ovary 1- 

 celled, 1-seeded. Styles 1-3, usually 2. Fruit a seed-like grain (caryopsis), 

 in some exotic species nut-like or berry-like. 



Spikelets falling from the pedicels entire, naked or enclosed in bristles or bur-like invo- 

 lucres, 1 -flowered, or if 2-flowered the lower flower staminate; no upper empty 

 glumes; rachilla not extending above the upper glume. 

 Spikelets round or somewhat compressed dorsally; empty glumes manifest; hilum 



punctiform. 

 Lemma and palet hyaline, thin, much more delicate in texture than the empty 



glumes. 

 Spikelets in pairs, one sessile and the other pedicellate. 



Tribe 1. ANDROPOQONEAE. 

 Spikelets not in pairs (Alopecurus, Polypogon, Cinna, etc.) 



Tribe 6. AGROSTIDEAE. 

 Lemma, at least that of the perfect flower, similar in texture to the empty glumes, 



or thicker and firmer, never hyaline and thin. 

 Lemma and palet membranous; the first glume usually larger than the rest. 



Tribe 2. ZOYSIEAE. 



Lemma and palet chartaceous to coriaceous, very different in color and ap- 

 pearance from the remaining glumes. Tribe 3. PANICEAE. 

 Spikelets much compressed laterally; empty glumes none or rudimentary; hilum 



linear. Tribe 4. ORYZEAE. 



Spikelets with the empty glumes persistent, the rachilla articulated above them, 1-many- 

 flowered; upper lemmas frequently empty; rachilla often produced beyond the 

 upper lemma. 

 Spikelets borne in an open or spike-like panicle or raceme, usually upon distinct 



pedicels. 

 Spikelets 1-flowered. 



Empty glumes 4; palet 1-nerved. Tribe 5. PHALARIDEAE. 



Empty glumes 2, rarely 1; palet 2-nerved (except in Cinna.) 



Tribe 6. AGROSTIDEAE. 



