Polygonaceae, the Buckwheat Family
Herbs with alternate entire leaves, stipules surrounding the stem above the base of each leaf, and small green, white or pink flowers without petals.
| 1a. Erect or ascending or prostrate or floating plants — 2. | |
| 1b. Scrambling or climbing plants, clinging by sharp recurved prickles on the 4-angled stems (flowers greenish or pink, summer) (Tear-thumb) — 32. | |
| 1c. Twining vines (flowers white or greenish, summer) — 33. | |
| 2a. Sepals 6, the 3 inner ones enlarging in fruit and surrounding the achenes; flowers in panicles — 3. | |
| 2b. Sepals 4 or 5 (occasional flowers may be found with 6 sepals, but the flowers are not in panicles) (summer) — 13. | |
| 3a. Leaves arrow-shape or halberd-shape, with 2 basal lobes (Sorrel) — 4. | |
| 3b. Leaves without basal lobes (Dock) — 5. | |
| 4a. Leaves halberd-shape, the basal lobes directed sidewise | Red Sorrel, Rumex acetosella. |
| 4b. Leaves arrow-shape, the basal lobes directed backward | Green Sorrel, Rumex acetosa. |
| 5a. The projecting wings of the fruiting calyx (known as valves) with sharp slender teeth | Bitter Dock, Rumex obtusifolius. |
| 5b. Valves entire or finely dentate, but without sharp slender teeth — 6. | |
| 6a. Pedicels straight, thickened toward the end, all regularly deflexed, 3-4 times longer than the fruiting calyx | Swamp Dock, Rumex verticillatus. |
| 6b. Pedicels slender, flexuous, spreading — 7. | |
| 7a. Leaves flat or nearly so — 8. | |
| 7b. Leaves with strongly crisped or wavy-curled margins; plants usually of cultivated grounds or waste places (5-10 dm., summer) — 12. | |
| 8a. With grain-like tubercles on all 3 valves of the fruit — 9. | |
| 8b. With grain-like tubercles on only one valve, or entirely lacking — 10. | |
| 9a. Valves broadly cordate, finely toothed | Water Dock, Rumex brittanica. |
| 9b. Valves triangular-ovate, entire or nearly so | Dock, Rumex mexicanus. |
| 10a. Valves oblong | Bloody Dock, Rumex sanguineus. |
| 10b. Valves broadly heart-shape — 11. | |
| 11a. Grain-like tubercle less than half as long as the valve | Patience Dock, Rumex patientia. |
| 11b. Grain-like tubercle more than half as long as the valve | Tall Dock, Rumex altissimus. |
| 12a. The grain-like tubercle on the valves of the fruit broadly ellipsoid, with rounded apex | Sour Dock, Rumex crispus. |
| 12b. Tubercle ovoid with tapering apex | Sour Dock, Rumex elongatus. |
| 13a. Flowers inconspicuous, in small axillary clusters; leaves jointed at the base (Knotweed) — 14. | |
| 13b. Flowers more or less conspicuous, in obvious spikes or racemes which terminate the stems or branches, or arise from the axils of the upper leaves — 18. | |
| 14a. Leaves sharply folded lengthwise (1-4 dm. tall) | Knotweed, Polygonum tenue. |
| 14b. Leaves flat or nearly so — 15. | |
| 15a. The small sepals pink or white at the margin (stems prostrate or ascending) — 16. | |
| 15b. Sepals greenish or yellowish throughout (stems erect or ascending) — 17. | |
| 16a. Leaves thin; common weed of dooryards and gardens | Knotweed, Polygonum aviculare. |
| 16b. Leaves thick and fleshy; a plant of sandy shores | Knotweed, Polygonum aviculare var. littorale. |
| 17a. Leaves narrowly lanceolate or linear-oblong; rare species | Knotweed, Polygonum ramosissimum. |
| 17b. Leaves broadly oblong, oval, or elliptical; common weed of yards and gardens | Knotweed, Polygonum erectum. |
| 18a. Leaves broadly triangular (3-7 dm. high; flowers white) | Buckwheat, Fagopyrum esculentum. |
| 18b. Leaves from linear to ovate or oblong — 19. | |
| 19a. Sepals 4; flowers in very long and slender spike-like racemes (4-10 dm. high) | Knotweed, Polygonum virginianum. |
| 19b. Sepals 5; flowers in spikes or racemes — 20. | |
| 20a. Flowers on slender pedicels, forming a loose raceme; leaves linear, jointed at the base (1-3 dm. high; flowers pink or white; chiefly near the Great Lakes) | Jointweed, Polygonella articulata. |
| 20b. Flowers sessile or nearly so, forming a spike or spike-like raceme — 21. | |
| 21a. Stipular sheaths at the base of the leaves ciliate at their upper margin — 22. | |
| 21b. Stipular sheaths not ciliate at the upper margin — 28. | |
| 22a. Sheaths with spreading borders — 23. | |
| 22b. Sheaths without a spreading border, appressed to the stem (Smartweed) — 24. | |
| 23a. Leaves ovate, acuminate; stem erect (1-2 m. high; flowers pink) | Prince’s Feather, Polygonum orientate. |
| 23b. Leaves oblong, obtuse or subacute; spreading or ascending plant of wet soil | Water Smartweed, Polygonum amphibium var. hartwrightii. |
| 24a. Peduncles with glandular hairs (5-15 dm. high) | Smartweed, Polygonum careyi. |
| 24b. Peduncles not glandular (1-8 dm. high) (Smartweed) — 25. | |
| 25a. Sepals beset with minute black dots — 26. | |
| 25b. Sepals white, pink, or red, not black-dotted — 27. | |
| 26a. Racemes drooping or nodding at the tip; achene dull-colored | Smartweed, Polygonum hydropiper. |
| 26b. Racemes erect; achene smooth and shining | Smartweed, Polygonum acre. |
| 27a. Sheaths smooth; leaves usually with a dark spot near the base | Smartweed, Polygonum persicaria. |
| 27b. Sheaths hairy; leaves not dark-spotted | Smartweed, Polygonum hydropiperoides. |
| 28a. Leaves obtuse or somewhat acute at the apex — 29. | |
| 28b. Leaves acuminate at the apex (5-15 dm. high; flowers white to pink) (Smartweed) — 30. | |
| 29a. Stem unbranched, erect, bearing a single terminal raceme (5-30 cm. high; flowers pink) | Bistort, Polygonum viviparum. |
| 29b. Stem branched, submerged in water or creeping on muddy shores (flowers pink) | Water Smartweed, Polygonum amphibium. |
| 30a. Raceme single or two; leaves broadly ovate-lanceolate, about 3 times as long as wide | Smartweed, Polygonum muhlenbergii. |
| 30b. Racemes numerous; leaves lanceolate, 4-6 times as long as wide — 31. | |
| 31a. Racemes drooping or nodding at the tip | Smartweed, Polygonum lapathifolium. |
| 31b. Racemes erect | Smartweed, Polygonum pennsylvanicum. |
| 32a. Leaves arrow-shape, the basal lobes pointing backward | Tear-thumb, Polygonum sagittatum. |
| 32b. Leaves halberd-shape, the basal lobes pointing sidewise | Tear-thumb, Polygonum arifolium. |
| 33a. The three outer sepals becoming conspicuously winged in fruit (False Buckwheat) — 34. | |
| 33b. The sepals all unchanged in fruit, except in size (Black Bindweed) — 35. | |
| 34a. Wings of the fruit with wavy-curled margins | False Buckwheat, Polygonum scandens. |
| 34b. Wings of the fruit flat | False Buckwheat, Polygonum dumetorum. |
| 35a. Leaf-sheaths with a ring of bristles at the base | Black Bindweed, Polygonum cilinode. |
| 35b. Leaf-sheaths without a ring of bristles | Black Bindweed, Polygonum convolvulus. |