210 IJRTICACEAE 



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. pcnnsylvanica. 

 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- 

 viont. 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-Jl. 



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 coroUoid. Corolla wanting. Stamens 2-9. Pistil of 

 2 or 3 united carpels, but ovary l-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. Choriz.\nthe. 

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



5. AC.VXTIIOGONUM. 



Involucres bract-like, 2-cleft. 6. Pterostegi.\. 



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

 Stigmas tufted. 



Sepals 6; styles 3; achenes triangular. 7. Ri'MEX. 



Sepals 4; styles 2; achenes lenticular. 8. Oxyki.v. 



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, trmicate. 10. Pek.sic.\klv. 



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



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



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



rOOtStOCks. 11. BiSTORTA. 



