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136 Polvygonaceae 
OXYRIA 
Herbs, perennial, low; juice acid. Leaves mostly basal. Flowers-in panicled ra- 
cemes, small, perfect; involucre none. Perianth unequally 4-parted, outer segments smaller 
than the inner. Stamens 6, included; filaments short, subulate, glabrous. Style short, 
2-parted, its branches divergent; stigmas 2, sessile, fimbriate, persistent. Fruit thin, lens- 
shaped, broadly winged. (Gk. oxys—sharp, sour; the leaves are sour.) W. C. E. 
0. digyna Hill (Mountain Sorrel) 
POLYGONUM KNOT-WEED | 
Herbs or shrubs, annual or perennial, terrestrial or aquatic. Stems erect or pros- 
trate or climbing or floating. Leaves alternate, sessile or petioled, entire or merely 
roughish, continuous with the stipular sheath or jointed to it; sheath cylindric or funnel- 
shaped or 2-lobed, often lacerate or fringed. Inflorescence various, terminal or axillary. 
Flowers small, normally perfect, green or white or pink or purple; pedicels not jointed, 
subtended by small sheaths. Perianth 4—-6-parted or -cleft; outer segments somewhat 
larger than the inner. Stamens 3—9, included or exserted; filaments filiform or dilated 
at base, glabrous. Style 2—-3-parted or -cleft, its branches included or exserted; stigmas 
capitate. Fruit lens-shaped*or 3-angled, rarely 4-angled, enclosed by or exceeding the 
perianth. (Gk. polys=many, gonu=knee, joint; because the stems are distinctly many- 
jointed. ) 
A. Plants erect to prostrate, but not vines; leaves cordate to attenuate at base. 
B. Leaf-blade jointed to the petiole (except subgenus DURAVIA), less than | cm. 
wide (except P. erectum); sheath 2-lobed, becoming lacerate; flowers either in 
axillary fascicles or in spike-like racemes with non-scarious bracts; filaments mostly 
dilated at base. 
C. Leaf-blade jointed to the petiole, not longitudinally 3-veined. 
. AVICULARIA (p. 136) 
CC. Leaf-blade not jointed to the petiole, longitudinally 3-veined. 
DuRAVIA (p. 138) 
BB. Leaf-blade not jointed to the petiole, at least some over | cm. wide; sheath 
not 2-lobed (except FP. alpinum); flowers in spike-like racemes (except subgenus 
ACONOGONON) ; bracts small, scarious, or none; filaments not or hardly dilated. 
D. Perennial or annual, without rhizomes, mostly lowland plants; sheath cylindric, 
truncate; stamens 48; akenes 3-angled or lens-shaped. PERSICARIA (p. 138): 
DD. Perennial, with horizontal and elongated or corm-like rhizomes, alpine or 
subalpine plants; sheath oblique; stamens 8; akenes 3-angled. 
E. Inflorescence of but | spike-like raceme, terminal; plants not growing in 
water nor particularly wet places. BIsTORTA (p. 139) 
EE. Inflorescence of more than | cluster, axillary and terminal; plants growing 
in wet places. ACONOGONON (p. 139) 
AA. Plants twining or climbing, vines; leaves sagittate or sagittate-cordate. 
TINIARIA (p. 140) 
Subgenus AVICULARIA (KNoT-WEED)—Leaves and the bracts jointed on the 
petiole, veinless or |-veined or obscurely pinnate-veined; petiole very short, adherent to the 
sheath; sheath 2-lobed or lacerate. Perianth 5—6-parted, usually more or less herbaceous. 
Stamens 3——8; the inner filaments dilated at base. Styles 3. Akenes 3-angled. 
A. Plants annual, glabrous or not; stems not woody, greenish, mostly striate, not scaly. 
B. Flowers axillary thruout. 
