210 URTICACEAE 



2. PARIETARIA (Tourn.) L. PELLITORY. 



Annual or perennial herbs, with diffusely branched, often pellucid stems, 

 polygamous. Leaves alternate, with 3-veined blades. Involucres of 2-6, more 

 or less united bracts. Flowers in axillary cymes. Perianth of 4, rarely 3, more 

 or less united sepals. Stamens 4, rarely 3, in the perfect and the staminate flow- 

 ers, in the pistillate ones wanting. Pistils solitary, in the staminate flowers 

 rudimentary; stigmas tufted. Achenes included, with a crustaceous pericarp. 



Leaf-blades lanceolate, 2-7 cm. long, twice as long as the petioles or longer. 



Plant comparatively dark green; stem densely puberulent; sepals lanceolate, acute. 



1. P. pennsyh'anica. 

 Plant very light green; stem long-villous ; sepals ovate, often obtuse. 



2. P. occidentalis. 

 Leaf-blades oblong or ovate-oblong, 0.5-2 cm. long, not twice as long as the petioles. 



3. P. obtusa. 



1. P. pennsylvanica Muhl. Annual, slender; stem weak, ascending, 1-4 

 dm. high, simple or branched; leaf-blades thin and flimsy, obtuse or acuminate 

 at the apex, acute or acuminate at the base; bracts of the involucre linear, 4-5 

 mm. long. Shaded banks or rocks: Ont. Fla. Mex. B.C. Plain Sub- 

 mont. My-Au. 



2. P. occidentalis Rydb. Annual; stem slender, erect, simple or branched 

 at the base, 1-4 dm. high; leaf-blades thin, light green, acute at the base, obtus- 

 ish at the apex, 1-4 cm. long, 5-18 mm. wide, sparingly pubescent; bracts of the 

 involucre linear, obtuse. Moist shaded places: Wash. Ida. Nev. Submont. 

 My-Au. 



3. P. obtusa Rydb. Annual; stem usually branched at the base, spreading, 

 5-20 cm. long, finely villous; leaf -blades obtuse; bracts of the involucres oblong 

 or narrowly oblong, obtuse; sepals ovate, obtuse, rarely acutish. Shady places: 

 Colo. Utah s Calif. Tex. Son. Submont. F-J1. 



FAMILY 37. POLYGONACEAE. BUCKWHEAT FAMILY. 



Herbs or shrubs, or in the tropics trees or vines, with alternate leaves. 

 Flowers perfect or rarely unisexual. Calyx inferior, of 2-6 more or less 

 united sepals, often corolloid. Corolla wanting. Stamens 2-9. Pistil of 

 2 or 3 united carpels, but ovary 1-celled, in fruit becoming a 1-seeded, tri- 

 angular or lenticular achene. 



Leaves without stipules; flowers or flower-clusters subtended by involucres of partly 



united bracts; stamens mostly 9. 

 Involucres from tubular to campanulate, of several united bracts. 



Involucres awnless, campanulate or turbinate, 4-8-toothed or -lobed. 



1. ERIOGONUM. 

 Involucres awn-pointed. 



Involucres herbaceous; flowers exserted; achenes lenticular. 



2. OXYTHECA. 



Involucres leathery or horny; flowers included; achenes 3-angled. 



Involucres with 3-6 awn-tipped spurs near the base, 1-3-flowered, in open 



dichotomous panicles. 3. CENTROSTEGIA. 



Involucres without spurs, 1-flowered. 



Involucres 6-angled, sulcate; filaments adnate to the base of the peri- 

 anth. 4. CHORIZANTHE. 

 Involucres 3-angled; filaments adnate to the whole tube of the perianth. 



5. ACANTHOGONUM. 



Involucres bract-like, 2-cleft. 6. PTEROSTEGIA. 



Leaves with sheathing stipules (ocreae) ; flower-clusters not involucrate; stamens 4-8. 

 Stigmas tufted. 



Sepals 6; styles 3; achenes triangular. 7. RUMEX. 



Sepals 4; styles 2; achenes lenticular. 8. OXYRIA. 



Stigmas not tufted. 



Leaf-blades jointed at the base; ocreae 2-lobed, becoming lacerate; filaments, 



at least the inner, dilated. 9. POLYGONUM. 



Leaf-blades not jointed at the base; ocreae not 2-lobed; filaments slender. 

 Ocreae cylindric, truncate. 10. PERSICARIA. 



Ocreae oblique, more or less open on the side facing the leaf. 



Herbs, not climbing or twining; sepals neither winged nor keeled. 



Flowers in simple spike-like racemes; plants with thickened tuberous 

 rootstocks. 11. BISTORTA. 



