The Jepson Herbarium
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Annual, perennial herbs to shrub.
Stem: prostrate to erect, 8–16-ribbed or 4–5-angled with ribs 0 or obscure; glabrous or papillate-scabrous.
Leaf: cauline, alternate, petioled or not; ocrea generally jointed to leaf, generally cylindric proximally, generally translucent distally, white or silvery, 2-lobed, glabrous, disintegrating to fibers or completely; blade linear, lanceolate, elliptic, ovate, or subround, entire.
Inflorescence: axillary, terminal, generally spike-like; peduncle 0; pedicels present or 0, included in to exserted from bractlets; flowers 1–7(10).
Flower: bisexual, base not stalk-like; perianth not enlarging, bell- to urn-shaped, glabrous, white or green-white to pink; perianth parts 5, fused 3–60[70]%, petal- or sepal-like, similar [or not], outer ± keeled or not, < to > inner, midveins generally a different shade or color than rest of perianth; stamens 3–8 (some staminodes or not), filaments or at least innermost free, wider at base, fused to perianth tube or not, anthers elliptic to oblong, white-yellow or generally pink to purple (orange-pink); styles (2)3, generally spreading, free or fused basally, stigmas 2–3, head-like.
Fruit: included or exserted, wings 0, angles (2)3, 1 face much narrower than other (1)2 or not; tip beak-like, yellow-green, brown, or black.
Seed: embryo curved.
± 65 species: ± worldwide; sect. Duravia restricted to w North America. (Greek: many, knee joint or seed, of uncertain meaning) [Costea 2005 Brittonia 57:1–27] Many species of sect. Polygonum with 2 kinds of fruit, differing in germination and morphology (summer fruit brown, ovate, tubercled to smooth; late-season fruit olive-green, lanceolate, smooth, 2–5 × > summer), but of little taxonomic importance. Mature, early-season plants with leaves, flowers, fruits needed for identification. Fls "closed" or "1/2-open" should be determined on herbarium specimens. Other taxa in TJM (1993) moved to Aconogonon, Bistorta, Fallopia, Persicaria.
Unabridged etymology: (Greek: poly, many, gony, knee joint, or gone, seed, of uncertain meaning)

Key to Polygonum

1. St 8–16 ribbed; leaf venation pinnate, abaxial 2° veins obvious; anthers white-yellow (sect. Polygonum)

2. Distal leaves <= distal flowers; inflorescence axillary, terminal

3. Margins of perianth lobes pink (red or white); fruit 1.3–2.3 mm ..... P. argyrocoleon

3' Margins of perianth lobes green-yellow, yellow (white, pink); fruit (2.3)2.5–3.5 mm ..... P. ramosissimum subsp. ramosissimum (2)

2' Distal leaves > to >> distal flowers; inflorescence axillary

4. Fr smooth to rough

5. Fr tip beaked, edges strongly concave ..... [P. fowleri subsp. fowleri]

5' Fr tip not beaked, edges flat

6. Plant ± succulent; leaf red-tinged, blade tips rounded; ocrea funnel-shaped proximally; flowers 1/2-open ..... P. marinense

6' Plant not ± succulent; leaf light-yellow-green to -blue-green, blade tips acute to acuminate; ocrea cylindric proximally; flowers closed ..... P. ramosissimum

7. St leaves 1–2.5 × branch leaves, blue-green fresh, dark-brown or black dry; pedicels 1–2 mm ..... subsp. prolificum

7' St leaves 2.1–3.5(4.2) × branch leaves, generally yellow-green fresh or dry; pedicels 2.5–6 mm ..... subsp. ramosissimum (2)

4' Fr striate-tubercled ..... P. aviculare

8. Perianth tube 40–57% of length ..... subsp. depressum

8' Perianth tube (15)20–40% of length

9. Ocreae generally ± persistent distally, especially on upper leaves; perianth 0.9–1.3(1.5) × as long as wide, ± pouched at base ..... [subsp. buxiforme]]

9' Ocreae soon disintegrating distally to fibers or completely; perianth 1.5–2.9 × as long as wide, not pouched at base

10. Lf blade (6)10–20 mm wide, 2–4.5 × as long as wide; flowers 3–8, ± crowded distally; fruit included or ± exserted ..... subsp. aviculare

10' Lf blade 0.5–6.8(8) mm wide, (3.4)4.2–15(19) × as long as wide; flowers 1–3(5), not crowded distally; fruit generally exserted

11. Ocrea (3)4–8 mm, distally disintegrating ± completely, veins obscure; lateral veins of leaves visible but not raised adaxially ..... [subsp. neglectum]]

11' Ocrea (6)8–12 mm, distally disintegrating to fibers, veins obvious; lateral veins of leaves raised adaxially ..... [subsp. rurivagum]]

1' St ± angled, ribs 0 or obscure; leaf venation parallel, abaxial 2° veins obscure; anthers pink to purple (orange-pink) (sect. Duravia)

12. Perennial to shrub

13. St erect, wiry; perianth 2.6–3.2 mm ..... P. bolanderi

13' St prostrate or ascending, not wiry; perianth (4.5)5–10 mm

14. Ocreae 15–20 mm, distally ± persistent; leaf blade midrib coarsely scabrous to ciliate abaxially; coastal dunes, scrub ..... P. paronychia

14' Ocreae 3–5 mm, distally deciduous; leaf blade midrib glabrous abaxially; mtns ..... P. shastense

12' Annual

15. Ocrea not jointed to leaf

16. Ocreae entire or shallowly dentate distally ..... P. bidwelliae

16' Ocreae disintegrating to fibers distally

17. St 4–40 cm; plant with branches 0 or widely spreading ..... P. californicum

17' St 1.5–5(8) cm; plant cushion-like

18. Ocreae distally disintegrating to straight fibers; fruit 2–2.5 mm ..... P. hickmanii

18' Ocreae distally disintegrating to curly fibers; fruit 1.2–1.6 mm ..... P. parryi

15' Ocrea jointed to leaf

19. Tips of perianth lobes acute to acuminate; fruit light-yellow or light- or green- to dark-brown, smooth or net-like with longitudinal ridges ..... P. polygaloides

20. Infl bract margin green, if white then scarious border < 0.2 mm wide

21. Fr lanceolate, 2–2.5 mm; inflorescence bracts lance-elliptic, appressed, rigid; stamens 5–8 ..... subsp. esotericum (2)

21' Fr ovate, 1.3–1.7 mm; inflorescence bracts linear to lance-linear, ± spreading, not rigid; stamens 3 ..... subsp. kelloggii

20' Infl bract margin white, scarious border (0.2)0.25–1 mm wide

22. Infl ovate to cylindric, generally distal, rarely also continuous from stem bases; fruit 1.3–2.1 mm, lance-ovate to ovate ..... subsp. confertiflorum

22' Infl narrowly cylindric, continuous from stem bases; fruit 2–2.5 mm, lanceolate ..... subsp. esotericum (2)

19' Tips of perianth lobes rounded; fruit black, smooth to minute- and/or striate-tubercled

23. Pedicels reflexed

24. Ocrea 3–5 mm; fruit 2–2.5 mm ..... P. austiniae

24' Ocrea 5–12 mm; fruit 3–5 mm

25. Fl closed; pedicel 2–6 mm; perianth tube 20–28% of perianth length ..... P. douglasii

25' Fl open or half-open; pedicel 0.5–1 mm; perianth tube 9–17% of perianth length ..... P. majus

23' Pedicels erect to spreading

26. Ocrea 1–5 mm, distally entire to dentate-torn; perianth 1.8–2.5 mm; fruit 1.8–2.3 mm ..... P. minimum

26' Ocrea 4–12 mm, distally disintegrating to fibers; perianth (2.5)3–5 mm; fruit 2.5–5 mm

27. Infl dense, flowers crowded distally ..... P. spergulariiforme

27' Infl not dense, flowers not crowded distally ..... P. sawatchense

28. St, ocrea papillate-scabrous; leaf blade elliptic to oblong-elliptic, margin papillate-fine-dentate; flowers, or at least some, open ..... subsp. oblivium

28' St, ocrea glabrous; leaf blade lance-linear to narrowly oblong or oblanceolate, margin smooth, entire; flowers closed ..... subsp. sawatchense

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Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html [accessed on month, day, year]
Citation for an individual treatment: [Author of taxon treatment] [year]. [Taxon name] in Jepson Flora Project (eds.) Jepson eFlora, [URL for treatment]. Accessed on [month, day, year].
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