POLYGONACEAE 377 



naceous Genera (Leaflets, 1: 17-50, 1904). Jones, M. E., [Notes on] Eriogonum (Contrib. 



11: 4-18, 1903). 



Leaves alternate or basal, always with sheathing stipules; involucre none. 



Sepals 5, equal and erect in fruit; stigmas capitate 1. POLYGONUM. 



Sepals unequal, the inner row erect and enlarging in fruit, the outer row reflexed; stigmas 

 tufted. 



Leaves not renif orm ; sepals 6 2. EUMEX. 



Leaves renif orm ; sepals 4 3. OXYRIA. 



Leaves opposite or basal, without sheathing stipules. 



Flower or flowers subtended by one or several distinct bracts, or none. 



Bract enlarged in fruit, 1-flowered, 2-lobed, 2-saccate on the back.. 4. PTEROSTEGIA. 

 Bracts not saccate or enlarged in fruit. 



Bracts none ; stamens 9 5. PHYLLOGONUM. 



Bracts woolly; flowers in clusters. 



Calyx glabrous ; stamens 3 ..6. NEMACAULIS. 



Calyx woolly ; stamens 5 to 9 7. HOLLISTERIA. 



Bracts naked ; stamens 3 8. LASTABEIAEA. 



Flowers borne in a tubular or turbinate involucre. 

 Involucral teeth spine- or bristle-tipped. 



Involucre mostly 5 or 6-toothed, usually 1-flowered; stamens 3, 6, or 9; involucral 



lobes usually tipped with hooked spines 9. CHORIZANTHE. 



Involucre 4 or 5-cleft (usually deeply), 2 to many -flowered ; stamens 9; involucral 



lobes ending in straight bristles 10. OXYTHECA. 



Involucre 3 to 8-toothed, the teeth not bristle-tipped 11. ERIOGONUM. 



1. POLYGONUM L. KNOTWEED. 



Herbs, some water plants, some woody at base. Leaves entire, alternate, 

 with scarious sheathing stipules ("sheaths"), these entire, ciliate or lacerate. 

 Inflorescence various, the flowers on jointed pedicels. Calyx red, white, or 

 sometimes greenish, in all ours 5-cleft or -parted, the divisions erect in fruit. 

 Stamens 4 to 9. Styles 2 or 3. Achene lenticular or triangular, enclosed in 

 the fruiting calyx. Embryo curved, lying in a groove at an angle of the 

 endosperm. About 160 species, all continents. (Greek polus, many, and gonu, 

 knee, on account of the nodose zigzag stem of many species.) 



A. Leaves not cordate. 



1. Flowers in axillary clusters or in spikes, racemes or panicles. 

 Leaves ample, not jointed to the petiole. 



Alpine or subalpine perennials with thick rootstocks; stamens 8; achene triquetrous. 



Flowers in a single dense terminal raceme; stem simple; herbage glabrous. Subgenus 



BISTORTA 1. P. bistortoides. 



Flowers in clusters or panicles; calyx articulated with the pedicel. Subgenus 

 ACONOGON. ^ 



Flowers numerous in panicles 2. P. alpinum. 



Flowers 2 to 4 in axillary clusters 3. P. davisiae. 



Low valleys or at middle altitudes; flowers in spikes (usually geminate or paniculate), 

 with small scarious bracts ; calyx appressed to the triquetrous or lenticular achene ; 

 stamens 4 to 8, filaments filiform; sheaths cylindrical, truncate, entire. Subgenus 

 PERSICARIA. 



Spikes 1 or 2; flowers red; stamens 5, exserted; achene lenticular; aquatic or marsh 

 perennials. 



Leaves elliptical or oblong ; spikes oblong or ovate, % to 1 inch long 



4. P. amphibium. 



Leaves ovate-lanceolate ; spikes more elongated, 1 to 3 inches long 



5. P. muhlenbergii. 

 Spikes several to many, in 2s or more or less paniculate; stamens 6 to 8, included; 



achene either lenticular or triangular; stream borders or marshy places. 

 Sheaths naked in age; spikes often drooping; sepals white or flesh-color; stamens 



6; annual 6. P. lapathifolium. 



Sheaths truncate or truncatish, fringed with bristles; spikes erect. 

 Calyx not punctate. 



Internodes strongly swollen above the nodes 7. P. fusiforme. 



Internodes not swollen. 



Herbage mostly glabrous ; annual 8. P. persicaria. 



Herbage strigillose ; perennial 9. P. hydropiperoides. 



Calyx punctate ; perennial 10. P. acre. 



