Polygonaceae ; 131 
BB.' Stipules scarious and sheathing; flowers not involucrate; juice usually sour or 
acrid; styles 2—-3; stamens fewer than 9 (except sometimes in Polygonum). 
E. Leaves kidney-shaped, wider than long; akene orbicular and broadly winged; 
perianth-lobes 4; stigmas 2. OxyRIA (p. 136) 
EE. Leaves not kidney-shaped, longer than wide: akene 3-angled or lens-shaped, 
‘ not winged ; perianth-lobes 5—-6 (4 in a few) ; stigmas 23. 
F.  Perianth-lobes 6, outer smaller and reflexed, inner erect and enlarging in 
fruit (except R. acetosella with very sour leaves) ; stigmas 3, tufted; akene 
3-angled. RUMEX (p. 134) 
FF. Perianth-lobes 5, rarely 4 or 6, all about equal and remaining so; stig- 
mas 2—3; capitate; akene 3-angled or lens-shaped. 
G. Plants not vines; akene 3-angled or lens-shaped. POLYGONUM (p. 136) 
GG. Plants vines; akene 3-angled. 
H. Plants not fleshy; calyx exceeding the mature akene; surface of akene 
without pinnate striation; basal. angles of leaves either projecting down- 
ward or else rounded. POLYGONUM (p. 136) 
HH. Plants rather fleshy; calyx only 14 as long as the akene; mature 
akenes with pinnate striation on each face; basal angles of leaves pointed, 
the points projecting outward. FAGOPYRUM (p. 140) 
PTEROSTEGIA 
Herbs, annual. Stems slender, weak, diffusely and dichotomously branched. 
Leaves opposite; entire or 2-lobed. Flowers solitary, sessile, in the forks of branches, in- 
volucrate; involucre foliaceous, sessile, of | bract, shorter than the flower, rounded and 
more or less 2-lobed; old involucre enlarged, scarious, reticulate, loosely enveloping the 
akene, gibbously 2-saccate on the back. Perianth 5-parted; segments all alike. Sta- 
mens on base of perianth, 5 or fewer. Fruit 3-angled, glabrous. * (Gk. pteron—wing, 
stege—a covering; referring to the bract-like involucre enclosing the solitary flowers.) W. 
P. drymarioides F. & M. 
CHORIZANTHE 
Herbs, annual (ours) or perennial, low. Stems dichotomously branched. Leaves 
mostly in a basal tuft. Flowers small, in heads, |—3 in the involucre (1 in ours) ; 
heads small; involucre tubular or funnel-form, sessile, 2—6-angled or -veined, 2—6- 
( toothed or -cleft, its divisions more or less divaricate and cusped or awned at tip. 
» Perianth 6-parted or -cleft. Stamens 9, rarely 3 or 6, on base of perianth or adherent 
to it. Styles linear; stigmas capitate. Fruit 3-angled, beaked. (Probably Gk. cho- 
a rion—a membrane, (xanthos=yellow. <Why?) ; : 
A. Plant 2.5—-10 cm. high, branching from the base; stamens inserted at the throat 
of the perianth-tube. E. C. watsoni T. & G. 
AA. Plant 15—45 cm. high, sparingly branched above; stamens inserted at the base 
of the perianth-tube. U. E.C. membranacea Benth. 
- OXYTHECA 
Herbs, annual. Stems slender, repeatedly dichotomously branched. Leaves all in 
a basal tuft. Flowers in clusters of | to several, small, perfect, pedicelled; clusters in- 
volucrate; involucre more or less stalked, campanulate or turbinate, herbaceous, not retic- 
ulate, 3—5-cleft; involucre-lobes erect or spreading, mostly with a straight slender awn at 
tip. Pedicels more or less exserted, intermingled with bractlets. Perianth 6-parted, col- 
