Rumex acetosella
Polygonaceae subfam. polygonoideae
common sheep sorrel, field sorrel, oseille, petite oseille, red sorrel, sheep dock, sheep sorrel, sour weed, sûrette
knotweed
erect or ascending, several from base, branched in distal 1/2 (in inflorescence), 10–40(–45) cm;
shoots variable.
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).
ocrea brownish at base, silvery and lacerated in distal 1/2;
blade normally obovate-oblong, ovate-lanceolate, lanceolate-elliptic, or lanceolate, occasionally, linear-lanceolate to almost linear, 2–6 × 0.3–2 cm, base hastate (with spreading, entire or sometimes multifid, dissected lobes), occasionally without evident lobes, then base broadly cuneate, margins entire, flat or nearly so, apex acute or obtuse.
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.
terminal, usually occupying distal 1/2–2/3 of stem, usually lax and interrupted to top, broadly or narrowly paniculate.
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.
1–3 mm.
(3–)5–8(–10) in whorls;
inner tepals not or slightly enlarged, normally 1.2–1.7(–2) × 0.5–1.3 mm (free wing absent or barely visible), base cuneate, apex obtuse or subacute.
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.
brown or dark brown, 0.9–1.5 × 0.6–0.9 mm.
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.
embryo usually straight or curved, rarely folded.
= 14, 28, 42.
Rumex acetosella
Polygonaceae subfam. polygonoideae
Rumex acetosella in the broad sense is an extremely variable and taxonomically complicated polyploid complex, which includes diploids, tetraploids, hexaploids, and octoploids. This complex (excluding more distantly related arctic-montane R. graminifolius and its allies) probably originated and developed mostly in southern Europe and southwestern Asia. Some races of R. acetosella now are distributed almost worldwide as introduced and often completely naturalized aliens.
Á. Löve (1941, 1983) assumed that in this group chromosome numbers are strictly correlated with morphology. In his opinion, every chromosome race represents a distinct species: diploid Rumex angiocarpus Murbeck [= Acetosella angiocarpa (Murbeck) Á. Löve]; tetraploid R. multifidus Linnaeus [= R. tenuifolius (Wallroth) Á. Löve = Acetosella multifida (Linnaeus) Á. Löve]; hexaploid R. acetosella in the narrow sense [= A. vulgaris (W. D. J. Koch) Fourreau, with gymnocarpous A. vulgaris subsp. vulgaris and angiocarpous A. vulgaris subsp. pyrenaica (Pourret ex Lapeyrouse) Á. Löve]; hexaploid R. graminifolius Rudolph ex Lambert [= A. graminifolia (Rudolph ex Lambert) Á. Löve]. However, the distribution given by Löve for these taxa seems unnatural. Studies by J. C. M. den Nijs and collaborators (den Nijs 1974, 1976, 1984; den Nijs and T. Panhorst 1980; den Nijs et al. 1980, 1985; see also W. Harris 1969, 1973) indicate that the situation is more complicated. They postulated the development of two major evolutionary lines into two ploidy complexes: a primary western Mediterranean one and a secondary eastern Mediterranean one. According to this scheme, polyploid races independently and spontaneously emerged (and still are emerging) within different ancestral populations.
The most widespread, almost cosmopolitan race, presumably native to the southwestern Mediterranean region, including southwestern and Atlantic Europe, which is common in North America, is characterized by a hexaploid chromosome set (2n = 42), nonmultifid lateral lobes of basal leaves, and angiocarpy (fruits are not easily separable from accrescent inner tepals). It was commonly and erroneously referred to as Rumex angiocarpus Murbeck, or R. acetosella subsp. angiocarpus (Murbeck) Murbeck. According to J. R. Akeroyd (1991), who in general followed the taxonomic revision of the group by J. C. M. den Nijs (1984), the correct name for this taxon is R. acetosella subsp. pyrenaicus (Pourret ex Lapeyrouse) Akeroyd (=Acetosella vulgaris subsp. pyrenaica (Pourret ex Lapeyrouse) Á. Löve). Gymnocarpous nonmultifid and multifid forms (R. acetosella subsp. acetosella and R. acetosella subsp. acetoselloides (Balansa) den Nijs, respectively) also occur in North America, but evidently rarely. The distributions of subspecies of R. acetosella in North America are poorly known. Keys and detailed descriptions for the subspecies were provided by den Nijs and Akeroyd. However, the tempting simplicity of the keys is somewhat suspicious. The alternative point of view (and an alternative key) may be found in Á. Löve (1983).
Rumex acetosella subsp. arenicola Mäkinen ex Elven was recently described from Greenland and reported for Scandinavia and arctic Russia (R. Elven et al. 2000). This entity seems to be morphologically transitional toward Rumex graminifolius (see discussion under that species below). According to Elven et al., it differs from other infraspecific entities of R. acetosella in having the following characters: leaves usually without basal lobes (as in R. graminifolius), with revolute margins; inflorescence sparsely branched; tepals and pedicels densely covered with red papillae (as in R. graminifolius). From R. graminifolius and related taxa (R. beringensis and R. krausei) it can be distinguished by narrower inner tepals (similar in size to those in other subspecies of R. acetosella). The distribution of subsp. arenicola and its relations to other taxa are in need of further study.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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 |
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