Chenopodium L.

Jonsell, B., Karlsson, 2005, Chenopodiaceae - Fumariaceae (Chenopodium), Flora Nordica 2, pp. 4-31 : 4

3. Chenopodium L.

Linnaeus, Sp. pi.: 218 (1753).

Literature. Aellen 1960-61, Engstrand & Gustafsson 1972-74, Hansen & Pedersen 1968, Jørgensen 1973, Uotila 1974, Uotila & Suominen 1976.

Annual or rarely perennial herbs; glabrous, farinose or glandular, rarely with ordinary hairs. Stem erect to ascending or procumbent, branched, often with stripes or ridges, subangular (i.e. in cross-section with rounded angles) to angular (i.e. with acute angles), only rarely terete. Leaves spirally arranged, the lowermost two sometimes (sub)opposite; petiole usually shorter than the blade; blade flat, entire, toothed or lobed; leaves upwards gradually smaller, narrower, more entire and with shorter petiole, in the inflorescence short-petiolate to sessile, with small, narrow, mostly entire blade.

Inflorescences axillary or terminal, often ± spike- or panicle-like, often reduced and diffuse; partial inflorescences leafy (subtended by well-developed leaves), bracteate (subtended by bracts), or ebracteate (not subtended by foliar structures or by extremely small ones); flowers in cymes or in clusters (glome rules) of one or more condensed cymes (rarely partly ± separate, solitary flowers). Flowers ebracteolate, often dimorphic (the terminal flower in each cyme bisexual or sometimes male and lateral flowers female). Tepals 3-5, free from the base or partly (rarely almost entirely) connate, contiguous or not, sometimes succulent in fruit, green or sometimes red, keeled or not. Stamens 5 or less, free or sometimes connate at base. Style fairly short, sometimes almost absent. Stigmas 2(-5), filiform. Fruit a nut, falling with the perianth or detached from it; pericarp membranous, easily detached from or ± firmly adherent to the seed. Seed vertical, horizontal or sometimes in an oblique position, lenticular, orbicular to ovate in outline; seed-coat usually hard, glossy.

Chromosome base-numbers x=8, 9. Polyploidy; up to hexaploids in Norden.

Subdivision of the genus. The genus can be divided into 3 easily recognizable subgenera, which have sometimes been treated as genera.

Subgen. Blitum (L.) Hiitonen (almost glabrous, glomerules in fruit succulent, red and very compact; x=9) includes species 1 and 2 and the rare casual C. exsuccum .

Subgen. Chenopodium ( ± farinose of vesicular hairs especially when young, glomerules less compact, dry; x=9) includes species 3-19 and most rare casuals.

Subgen. Ambrosia A.J. Scott (not farinose, with glands as well as ordinary hairs, inflorescences of dry glomerules and/or solitary flowers, often dichasial; x=8, 9) includes species 22-24 and the rare casuals C. anthelminticum , C. aristatum , C. carinatum , C. cristatum , C. melanocarpum , C. multifidum , C. pseudomultiflorum , and C. pumilio .

Biology. Wind-pollinated. At least in some species the seeds can survive in soil for decades or even centuries.

Many species have strict photoperiod demands; plants adapted to short-day conditions do not flower until autumn.

Variation. The genus includes several very widespread weedy species with great plasticity in vegetative characters (such as branching habit and leaf and inflorescence shape). The variation of these characters is controlled both genetically and environmentally and is, to some extent, parallel in most species. Also in floral characters the variation is wide and in many cases overlapping.

Photoperiod affects the morphology of inflorescences and leaves. Diffuse, panicle-like inflorescence types and less toothed leaves are more common in long-day conditions, whereas more compact, spike-like types and more toothed leaves dominate in short-day conditions.

Numerous exotic taxa have been brought to Norden, mainly from more southern regions, and also alien strains and close relatives of our resident species, especially of C. album ; they are often adapted to short-day conditions and do not develop normally in Norden. Often they do not flower until very late (if at all), and then the temperature is too low for seed production; thus parts which are essential for identification are often missing. Due to the light conditions the leaves and inflorescences are often fairly different from plants growing in their original area. Such plants have been much collected; often they were given various infraspecific names or were taken for hybrids.

Hybridization. Due to the great morphological variation within species, most hybrids are extremely difficult to recognize. Seed or pollen sterility is no proof of hybridization, because it may be caused by other factors, especially late flowering. Verified hybrids are mainly between species on the same ploidy level. However, hybridization between the rare casuals C. carinatum , C. cristatum , C. melanocarpum and C. pumilio seems to be relatively common.

Many hybrids have been reported from Norden, and in the herbaria there is a large material labelled as hybrids. However, most of the reports seem to be based on misidentification of alien taxa or strains growing under unsuitable photoperiodic conditions. In this treatment only the hybrids C. album x opulifolium , C. carinatum x cristatum , C. cristatum x melanocarpum and C. ficifolium x suecicum have been accepted.

Diagnostic characters. Seed characters are important in the identification because they vary relatively little within species. Seed position, size and shape (ratio length/width), shape of margin and especially seed-coat ornamentation (Figs 2, 3) are of importance.

The ornamentation varies in different parts of the seed: in vertical seeds it is best studied in the middle part of one of the faces, and in horizontal seeds on the lower face not too close to the margin or the centre. The descriptions given here refer, if not otherwise indicated, to these parts.

Terminal flowers sometimes deviate even in taxa with ± monomorphic flowers. They are often larger than lateral ones, and their tepals sometimes have more distinctly raised keels.

Leaf characters given refer, unless otherwise indicated, to fully developed leaves in the middle portion of the main stem. In all taxa there is a gradual change along the shoot, upper leaves being smaller, narrower, less toothed or lobed, and more short-petiolate. In some taxa lower leaves, middle leaves, and bracts have been described separately. The lowermost stem leaves are smaller and less toothed than the next ones; they wither early and have usually been left out from the descriptions.

1 Plant with glands or glandular hairs; aromatic.........................2

- Plant glabrous or farinose; not aromatic (but sometimes stinking)....................................................................................4

2 Leaves coarsely serrate (sometimes deeply so); flowers sessile, in glomerules.................................22. C. ambrosioides

- Leaves pinnatifid; many flowers single, in lax cymes.............3

3 Tepals with distinctly stalked glands, rounded at the back; leaves shallowly pinnatifid....................................23. C. botrys

- Tepals with subsessile glands, with a cristate keel on the back; leaves deeply pinnatifid................24. C. schraderianum

4 Perennial, somewhat viscid; leaf-blades triangular with almost entire margin....................................3. C. bonus-henricus

- Annual, not viscid; leaf-blades usually not triangular (if triangular then with toothed or lobed margin)..........................5

5 Perianth becoming red and succulent in fruit; flowers in ± sessile, axillary glomerules; leaf-blades ± triangular, glabrous....................................................................................6

- Perianth not becoming red and succulent in fruit; flowers in lax cymes or in glomerules (but then usually not all axillary); leaf-blades rarely triangular, often farinose (especially when young)...........................................................7

6 Inflorescence bracteate to the top; edge of seed flat or usually ± grooved......................................................1. C. foliosum

- Apical part of inflorescence ebracteate; edge of seed rounded or usually ± keeled..............................2. C. capitatimi

7 Leaf-blades with ± cordate base, each margin with 1-3 angles or acute to acuminate lobes (or large teeth) but otherwise entire; seeds 1.6-2 mm...................10. C. hybridum

- Leaf-blades different (usually with ± cuneate base and rarely angled or with acute lobes); seeds less than 1.6 mm ........8

8 Leaf-blades ovate with entire margin, not farinose; most or all flowers in lax or fairly compact, usually manyflowered cymes ..........................................8. C. polyspermum

- Leaf-blades usually toothed or lobed, if entire then usually farinose; most flowers in glomerules forming a panicle- or spike-like inflorescence............................................................9

9 Most flowers with usually 3 tepals and a vertical seed; the terminal flower of each cyme with 5 tepals and a horizontal seed 10

- All flowers with 5 tepals and a horizontal seed......................12

10 Leaves green above, bluish and farinose beneath; blades of lower leaves elliptic, ovate or lanceolate ............6. C. glaucum

- Leaves green on both surfaces (sometimes red-tinged); blades of lower leaves triangular, broadly ovate or almost rhombic...................................................................................11

11 Tepals of lateral flowers connate to near apex, forming a sac surrounding the nut; leaf-blades usually triangular to broadly rhombic.......................................4. C. chenopodioides

- Tepals of lateral flowers connate halfway or less; leaf-blades usually ovate to rhombic...........................5. C. rubrum

12 Plant stinking when fresh, usually procumbent to ascending, strongly farinose; leaf-blades ovate to rhombic, fairly wide; leaf-margin sometimes angled at the widest point but otherwise entire............................................11. C. vulvaria

- Different (if stinking then lower leaves with ± lobed blade); leaf-margin usually toothed or lobed; if entire, the leaf-blades usually very narrow .............................................13

13 Edge of seed distinctly keeled; pericarp firmly adherent to seed; tepals with a conspicuous keel near apex; leaf-margin distinctly serrate ........................................9. C. murale

- Edge of seed convex or indistinctly keeled; pericarp free or adherent to seed; tepals with a rounded back or keeled along most of their length; leaf-margin entire to dentate or serrate.....................................................................................14

14 Inflorescences not or very sparsely farinose; blades of lower leaves ± broadly triangular, usually dentate 7. C. urbicum

- Inflorescences farinose (especially when young); leaf-blades different.......................................................................15

15 Leaf-blades at least twice as long as wide, lower surface densely farinose; margins entire (or sometimes 1 lobe-like tooth on either or both margins at the widest point of the blade); apex acute, mucronate.......................12. C. pratericola

- Leaf-blades as long as wide or longer than wide, lower surface less densely farinose (mature leaves often very slightly so); margins at least in middle and lower leaves usually ± serrate (if entire then apex ± obtuse, acute or acuminate)..............................................................................16

16 Seeds 0.8-1 mm, with pitted seed-coat; lower leaves with ovate to rhombic, fairly narrow, distinctly 3-lobed blade, midlobe comprising c. 2/3 of the length of the blade, with parallel and coarsely toothed margins 13. C. ficifolium

- Seeds 1-1.5 mm, with smooth, striate or pitted seed-coat; lower leaves different (if blade 3-lobed then midlobe only c. 1/2 of the length of the blade).............................................17

17 Leaf-blades about as long as wide, distinctly 3-lobed .......18

- Leaf-blades clearly longer than wide, entire to slightly 3-lobed....................................................................................19

18 Plant stinking when fresh; midlobe of lower leaves usually with several coarse teeth, basal lobes each usually with a coarse tooth......................................................20. C. hircinum

- Plant not stinking; midlobe of lower leaves entire to serrate, basal lobes small, without prominent teeth ......................................................................21. C. opulifolium

19 Seed-coat distinctly honeycomb-pitted; leaf-blades acuminate, usually with few teeth ....................19. C. berlandieri

- Seed-coat smooth, striate or indistinctly pitted; leaf-blades obtuse to acute, toothed to entire ................. 20

20 Seeds orbicular in outline, seed-coat slightly pitted; leaf-blades usually with sharply dentate to serrate, rarely entire margin, usually somewhat 3-lobed; inflorescences bracteate almost to the top, bracts usually toothed; stem soft ..... 14. C.suecicum

- Seeds broadly ovate to almost orbicular in outline, seed-coat smooth or slightly radially striate; leaf-blades with entire or variously toothed margin, rarely somewhat 3-lobed; upper part of inflorescences ebracteate, bracts with entire margin; stem hard.................................................21

21 Seeds broadly ovate, 1-1.2 mm; blades of lower leaves often narrowly oblong to elliptic (i.e. with parallel sides) or trullate, with entire to regularly dentate margin and obtuse apex; inflorescence spike-like.........................................22

- Seeds suborbicular, (1-)1*2-1.5 mm; blades of lower leaves various but not oblong to elliptic; margin entire to irregularly serrate (teeth sometimes lobe-like), apex acute; inflorescence panicle- or spike-like........................ 23

22 Leaf-blades up to 2.5(-3.5) cm, more than twice as long as wide, those of lower leaves trullate, fairly acute .......................................................................17. C. striatiforme

- Leaf-blades usually at least 3 cm, less than twice as long as wide, elliptic to oblong, obtuse...........................18. C. strictum

23 Seeds 1.2-1.5 mm; inflorescence panicle- or spike-like, glomerules usually fairly large; blade of middle leaves to 5(-7) cm, with entire or irregularly serrate to dentate margin, teeth obtuse, not lobe-like..............................15. C. album

- Seeds c. 1 mm; inflorescence spike-like, glomerules small; blade of middle leaves often 6-8 cm, usually slightly 3-lobed; margin serrate with few but often coarse teeth .................................................16. C. missouriense

Chenopodium auricomiforme Murr & Thell ., C. phillipsianum Aellen var. galpinii Aellen and C. pseudauricomum Murr were published from S Sk Lackalänga (see Hylander 1971), but the material determined to C. auricomiforme is here referred to C. auricomum , that of the other two species to C. mucronatum (rare casuals).