Polygonaceae subfam. Polygonoideae

Eaton

Bot. Dict. ed. 4, 30. 1836

Common names: Knotweed
Treatment appears in FNA Volume 5. Treatment on page 479. Mentioned on page 216, 217, 218.
Trees, shrubs, vines, or herbs, perennial or annual, homophyllous (heretophyllous in some species of Polygonum); root fibrous or a solid taproot, rarely tuberous. Stems usually prostrate to erect, sometimes scandent, not scapose, rarely with recurved spines (some species of Persicaria), glabrous or pubescent, sometimes glandular; nodes usually swollen; branches free (adnate to stems distal to nodes and appearing to arise internodally in Polygonella); tendrils absent (except in Antigonon and Brunnichia). Leaves deciduous (persistent in Coccoloba and sometimes more than 1 year in Antigonon and Polygonella), basal or basal and cauline, rarely cauline only, mostly alternate; ocrea present, persistent or deciduous, cylindric to funnelform, chartaceous, membranous, coriaceous, or, rarely, foliaceous or partly so; petiole present or absent, rarely articulate basally (Fagopyrum, Fallopia, Polygonella, Polygonum), rarely with extrafloral nectaries (Fallopia, Muehlenbeckia); blade simple with entire margins, rarely undulate or lobed. Inflorescences terminal or terminal and axillary, spikelike, racemelike, paniclelike, cymelike, or, rarely, capitate, comprising simple or branched clusters of compound inflorescences; bracts absent; peduncle spreading to erect, sometimes absent; clusters of flowers subtended by connate bracteoles forming persistent membranous tube (ocreola), awnless. Flowers usually bisexual, sometimes bisexual and unisexual on same plant, rarely unisexual only, 1–20+ per ocreate fascicle, often with stipelike base distal to articulation; perianth often accrescent in fruit, often greenish, white, pink, yellow, red, or purple, usually unwinged and unkeeled (winged or, sometimes, keeled in Fallopia, rarely keeled in Polygonum), campanulate or urceolate, sometimes membranous, indurate, or fleshy in fruit, rarely developing raised tubercles proximally (Rumex), glabrous or pubescent, sometimes glandular or glandular-punctate; tepals 2–6, usually in 2 whorls, distinct or connate proximally and forming tube, petaloid or sepaloid, monomorphic or dimorphic; nectary a disk at base of ovary or glands associated with bases of filaments; stamens usually (1–)6–9, staminodes rarely present; filaments distinct, or connate basally and sometimes forming staminal tube, free or adnate to perianth tube; pistils (2–)3(–4)-carpellate; ovary 1-locular (sometimes with vestigial partitions proximally); ovule 1, orthotropous or, rarely, anatropous, placentation basal or free-central; styles 1–3, erect to spreading or recurved, distinct or connate proximally; stigmas peltate, capitate, fimbriate, or penicillate. Achenes yellowish, brown, red, or black, homocarpic (sometimes heterocarpic in Polygonum), winged or unwinged, usually 2–3-gonous, sometimes discoid, biconvex, or spheroidal, rarely 4-gonous. Seeds: embryo usually straight or curved, rarely folded.

Distribution

Mainly temperate regions of North America.

Discussion

Genera 28, species ca. 850 (16 genera, 160 species in the flora).

Morphological (K. Haraldson 1978; L.-P. Ronse Decraene and J. R. Akeroyd 1988; Ronse Decraene et al. 2000; Hong S. P. et al. 1998) and molecular (A. S. Lamb Frye and K. A. Kron 2003) data provide support for separation of Persicaria from Polygonum. Further studies are needed to elucidate the relationships of allied genera, particularly Aconogonon, Bistorta, and Koenigia with Persicaria, and Fallopia and Polygonella with Polygonum.

Key

1 Tendrils present; plants vines > 2
1 Tendrils absent; plants trees, shrubs, or herbs, rarely vinelike shrubs > 3
2 Perianths pink to purple or, rarely, white or yellow, membranous; pedicels not 3-winged Antigonon
2 Perianths green to greenish yellow, indurate; pedicels 3-winged, 1 wing more prominent and becoming greatly expanded in fruit Brunnichia
3 Plants trees or shrubs; tubes of pistillate flowers becoming fleshy in fruit Coccoloba
3 Plants herbs, subshrubs, or, rarely, vinelike shrubs; tubes of pistillate flowers rarely becoming fleshy in fruit > 4
4 Tepals 6 > 5
4 Tepals 3, 4, or 5 > 7
5 Flowers unisexual; outer 3 tepals of pistillate flowers each with apex ending in stout spine Emex
5 Flowers bisexual or, rarely, unisexual; outer 3 tepals each without apex ending in stout spine > 6
6 Achenes winged; inner tepals of fruiting perianths nonaccrescent; stamens (6-)9 Rheum
6 Achenes unwinged; inner tepals of fruiting perianths usually accrescent; stamens 6 Rumex
7 Herbs annual; tepals 3 [4]; stamens (1-)3[-5] Koenigia
7 Herbs perennial or annual, or shrubs; tepals 4-5; stamens 3-8 > 8
8 Tepals 4; achenes lenticular, winged; leaves mostly basal Oxyria
8 Tepals 4 or 5; achenes 3-gonous, discoid, biconvex, spheroidal, or 4-gonous, unwinged or essentially so; leaves cauline or basal and cauline, rarely mostly basal > 9
9 Branches adnate to stems, appearing to arise internodally Polygonella
9 Branches not adnate to stems, not appearing to arise internodally > 10
10 Plants shrubs, vinelike; flowers unisexual, tubes of pistillate flowers becoming fleshy in fruit Muehlenbeckia
10 Plants herbs or, if shrubs, not vinelike; flowers bisexual or, rarely, unisexual, if unisexual then tubes of pistillate flowers not becoming fleshy > 11
11 Outer tepals winged or keeled > 12
11 Outer tepals unwinged and unkeeled > 13
12 Outer tepals winged (keeled in F. ciliondis and, usually, F. convolvulus); ocreae chartaceous, tan to brownish, glabrous or scabrous to variously pubescent, never 2-lobed distally Fallopia
12 Outer tepals keeled; ocreae often hyaline, silvery, glabrous, 2-lobed distally Polygonum
13 Leaves mostly basal, some cauline; inflorescences terminal, spikelike; stems simple Bistorta
13 Leaves cauline; inflorescences terminal and axillary or axillary; stems usually branched, rarely simple > 14
14 Achenes strongly exserted; perianths nonaccrescent; tepals distinct Fagopyrum
14 Achenes included or exserted; perianths accrescent or nonaccrescent; tepals connate to 2/3 their lengths. [15. Shifted to left margin.—Ed.] > 15
15 Ocreae often hyaline, silvery, glabrous, 2-lobed distally, often disintegrating into fibers or completely Polygonum
15 Ocreae chartaceous, usually tan, brown, or reddish, rarely silvery, glabrous or scabrous to variously pubescent, never 2-lobed distally, often tearing with age > 16
16 Inflorescences spikelike, paniclelike, or capitate; tepals 4 or 15, connate 1/ 2/ 3 their length (less than 5 their length in P. wallichii); stamens 5-8 Persicaria
16 Inflorescences racemelike or paniclelike; tepals 5, connate ca. 1/ 4 their length; stamens 8 Aconogonon