POLYGONACEAE 
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appearing before the leaves. Stamens inserted on a concave, often oblique 
disk. Ovary borne in a cup-shaped disk. Stigmas 2 to 4, dilated or 
linear. (Classical Latin name of the poplar.) 
L P. fremonti Wats. Common Cottonwood. Trees 8 to 14 m. high 
with a broad crown; leaves deltoid or roundish, broader than long, yel¬ 
lowish-green, alike on both faces, the margin crenate except at the ab¬ 
ruptly pointed apex and somewhat heart-shaped or truncate base; sta¬ 
mens 60 to 80.—Interior creeks and rivers. The wood is used by desert 
settlers for fencing, and is sometimes sawn into box shook for fruit and 
other shipments. 
2. P. trichocarpa T. & G. Black Cottonwood. Tree 5 to 8 m. high; 
leaves ovate, longer than broad, serrulate, dark green and shining above, 
rusty or silvery beneath; stamens 40 to 60.—Along streams. 
POLYGONACEAE. BUCKWHEAT FAMILY 
Herbs or somewhat woody plants with entire leaves. Stipules none or 
present in the form of sheaths above the swollen joints of the stem. 
Flowers small, often borne in an involucre. Calyx 3 to 6-cleft. Corolla 
none. Stamens 4 to 9. Ovary superior, 1-celled, becoming an achene 
which is commonly 3-angled.—About 700 species, mostly in the north 
temperate zone. 
Leaves with sheathing stipules ; involucre none. 
Sepals 5, equal and erect in fruit. 
Leaves elliptical to lanceolate or linear.1. Polygonum. 
Leaves triangular-cordate or sagittate.2. Fagopyrum. 
Sepals 6, unequal, the inner row erect and enlarging in fruit, the outer row 
reflexed in fruit. 
Sepals of 2 kinds.3. Rumex. 
Sepals all alike, withering-persistent under the 3-winged fruit..4. Rheum. 
Leaves without stipules; involucre present. 
Involucre bract-like, 1-flowered, enlarged in fruit, 2-lobed, 2-saccate on back; 
leaves opposite, broad...5. Pterostegia. 
Involucre tubular or top-shaped : leaves alternate or in whorls, or mostly basal. 
Involucre 5 to 6-toothed, the teeth spine-tipped, often hooked. 
6. Chorizanthe. 
Involucre 3 to 8-toothed, the teeth not bristle-tipped...7. Erigonum. 
1. POLYGONUM L. Knotweed 
Herbs with conspicuous stipules sheathing the prominent joints of the 
stem. Flowers white, red or greenish. Calyx 5-parted, often petal-like. 
Stamens 4.to 9. Styles 2 or 3. Achene triangular or lens-shaped. (Greek 
polus, many, and gonu, knee, on account of the nodose zigzag stem of 
many species.) 
Leaves mostly broad or ample, not jointed to the petiole. 
Spikes 1 or 2 ; flowers red ; stamens 5, exserted. 
Leaves elliptical or oblong; spikes 1.2 to 2.4 cm. long.1. P. amphibium. 
Leaves ovate-lanceolate; spikes 2.4 to 7.2 cm. long....2. P. muhlenbergii. 
Spikes several to many; flowers greenish, white or flesh-color; stamens 6 to 
8, included. 
Sheaths naked in age; spikes often drooping; flowers white or flesh- 
color....3. P. lapathifolium. 
Sheaths trunacte, fringed with bristles; spikes erect; flowers greenish. 
4. P. acre. 
