Linnaeus, Sp. Pl. 1: 219. 1753.
erect to sprawling, simple to much-branched, 1-30 dm, sparsely to densely farinose.
nonaromatic; petiole 1-2.5 cm, shorter than blades or occasionally longer; blade ovate-lanceolate to rhombic-lanceolate or broadly oblong, 1-5.5(-12) × 0.5-3.8(-8) cm, base narrowly to broadly cuneate, margins sinuous-dentate to shallowly serrate or entire, apex acute to subobtuse, farinose abaxially.
glomerules or occasionally 1-flowered peduncles in terminal and lateral compound spikes, 2-19 cm; glomerules subglobose, 3-4 mm diam.; bracts absent.
perianth segments 5, distinct nearly to base; lobes ovate, ca. 1 × 1.1 mm, apex obtuse, keeled, farinose, largely covering fruit at maturity; stamens 5; stigmas 2, 0.2-0.3 mm.
depressed-ovoid; pericarp nonadherent, occasionally adherent, smooth to papillate.
lenticular, margins round, 0.9-1.6 mm diam.; seed coat black, smooth, indistinctly granulate and/or radially grooved, or with faint reticulate-rugose ridges.
Fruiting late summer-fall. Disturbed soils in open habitats; 0-1400 m; introduced; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo; probably mostly native in Europe.
, one of the worst weeds and most widespread synanthropic plants on the Earth, in its broad circumscription is also among the most polymorphic plant species. It is a loosely arranged aggregate of still insufficiently understood races. Hundreds of segregate microspecies and infraspecific entities (including nomenclatural combinations) of the
aggregate have been described and/or recognized by various authors. Some authors have recognized numerous segregate intergrading species, while others have developed elaborate infraspecific hierarchies with numerous subspecies, varieties, forms, and even numerous subforms (e.g., B. Jüttersonke and K. Arlt 1989), or have combined both approaches. Neither approach has brought satisfactory and uncontroversial results.
It is evident that most recent evolutionary processes within the group were greatly affected by anthropic factors, including extensive recent invasions, hybridization between previously geographically isolated taxa, poly-ploidy, intensive selective processes and mutagenesis in synanthropic habitats, gene drift, and so forth. All of these modern factors further complicated the taxonomic situation. Consequently, no infraspecific taxa are formally recognized in the present treatment. We attempt, however, to outline below the most common or noteworthy groups currently placed in
sensu lato. Although we list such groups under binomials, they should be considered here as informal groupings rather than accepted species.
It should be also kept in mind that many enigmatic and deviant forms of the
aggregate are in fact hybrids with other (occasionally several) species, and between infraspecific entities.
Aellen & Iljin),
Aellen), and some other species.
sensu stricto: plants usually erect, ± farinose, at maturity becoming yellowish green with reddish tint; not profusely branched, branches in proximal
/2 mostly arching, in distal part straight and upright; proximal and middle cauline leaf blades ovate to weakly 3-lobed, margins dentate, teeth usually small and densely arranged; inflorescences normally condensed, spicate; seeds variable (especially in hybrids and deviate forms) but most often 1-1.25 mm diam., seed coat smooth or nearly so.
The typical form of
is widespread in North America, but occurs sporadically and less commonly than the following form.
Muhlenberg ex Willdenow: plants usually robust, erect to ascending, sparsely to moderately farinose, at maturity usually dark green; profusely branched, especially in inflorescence, branches arcuate and spreading; proximal and middle cauline leaf blades elliptic or elongate to narrowly lanceolate, base cuneate to narrowly cuneate, margins entire or with few teeth (usually in proximal
/2); inflorescences normally much-branched, loosely paniculate, often nodding; seeds variable in size.
is probably the most widespread and variable group of presumably hybridogenous forms in North America. I. J. Bassett and C. Crompton (1982) considered
to be a form of
. It appears that the difference between these two taxa is based on habitat---
grows in cultivated ground and has an erect growth habit whereas
grows in vacant lots, roadsides, etc., and has a more sprawling habit.
Bertoloni: plants similar to
, but less robust, usually with ascending branches, sparsely to moderately farinose, at maturity dark green to yellowish; profusely branched, especially in inflorescence; proximal and middle cauline leaf blades ovate to broadly lanceolate (distal ones lanceolate), base rounded to cuneate, margins normally entire or with few teeth at base; inflorescences much-branched, loosely paniculate, nodding; seeds large, ca. 1.5 mm diam., seed coat smooth to irregularly and indistinctly grooved.
Forms similar to the European ones occur in North America, but their exact distribution and taxonomic status are uncertain. The taxonomy of
was discussed in detail by F. Dvo ák (1984).
Murr, and similar taxa including
(J. B. Scholz) Murr: plants usually erect, sparsely to moderately farinose, or becoming glabrous, at maturity usually light green to dark green; branched in middle portion of stem and in inflorescence, branches straight to arcuate; proximal and middle cauline leaf blades elliptic or elongate to narrowly lanceolate, base cuneate to narrowly cuneate, margins variously 3-lobed and/or dentate, teeth few, usually large (especially in proximal
/2); inflorescences much-branched, loosely paniculate; seeds variable, but predominantly ca. 1 mm diam., seed coat with indistinct elongate depressions and radial grooves, occasionally nearly smooth.
was repeatedly reported from North America, mostly by European authors, and indeed, similar forms occur in the New World. However, their taxonomy is far from clear, and because of that they are treated here collectively, as an informal group of
. Some forms are transitional toward
. Numerous forms of "C. syecucyn" were identified in North America as
sensu stricto or
. The name
auct. was also widely misapplied.
Iljin: plants usually with erect or ascending (rarely prostrate) main stem, sparsely farinose to almost glabrous, deep olive green, at maturity becoming yellowish or reddish; not profusely branched, proximal branches arcuate to almost prostrate; proximal and middle cauline leaf blades ovate-deltoid, 3-lobed to indistinctly 3-lobed, margins of lobes entire or nearly so, teeth (if present) small and obtuse; inflorescences normally compact, spicate; perianth segments spreading at maturity, not covering fruit; seeds 1-1.4 mm diam., seed coat indistinctly pitted with weak radial grooves.
is a characteristic nonweedy alluvial taxon of sandy and gravelly river shores of northern Eurasia (northeastern European Russia, Siberia), related to
(see below). Several specimens collected in Alaska are probably referable to
; the available scarce material is not sufficient to confirm this.
Andrzejowsky: similar in morphology to
, this is a characteristic, predominantly nonweedy alluvial species confined to sandy habitats of eastern Europe and western Siberia. It has been reported as introduced in Colorado (W. A. Weber and R. C. Wittmann 1992); this record was probably based on misidentification of
Aellen, and other similar forms: plants usually exceptionally robust, to 20-30 (occasionally more) dm, erect, ± densely farinose (mealy pubescence of young leaves usually reddish or yellowish), at maturity becoming yellowish green, yellow to deep beet red; variously (but usually not profusely) branched; proximal and middle cauline leaf blades large (to 15 cm), ovate to distinctly 3-lobed, margins dentate to ± entire; terminal inflorescences normally condensed, spicate (in some forms lax but large), lateral inflorescences usually weakly developed; seeds variable but most often ca 1.2 mm diam. or larger, seed coat smooth or nearly so.
These taxa are probably all native to southern and southeastern Asia, where they were occasionally cultivated as ancient leaf vegetables and pseudocereals. In Japan and eastern China they were usually known as
(Makino) Nakai, and in India and western China as
D. Don. Other forms, such as
Coste & Reynier, are of uncertain origin.
Aellen was described from Europe as an alien species supposedly introduced from Australia, but then its North American origin was suggested. Probably the forms discussed evolved independently in different parts of Eurasia and, consequently, represent different taxa of the
aggregate. Despite several painstaking efforts (e.g., P. Aellen 1929c; F. Dvo ák 1992), their taxonomy still remains confused and is in need of further experimental studies.
Aellen: plants with thick leaves and reduced size are possibly a phenotypic response to dry northern prairie habitats. It has been reported from southern Manitoba and northern parts of the upper Midwest.
Aellen: a confusing taxon because of its mixed typification. It appears to be a native form of
that flowers in mid September regardless of when it germinated. The inflorescences are somewhat reminiscent of
. It occurs in the United States in the central lowlands and part of the Appalachian plateau and is designated a weed (D. T. Patterson et al. 1989).