Chenopodium, L.

Brenan, J. P. M, 1954, Chenopodiaceae (part: Chenopodium), Flora of Tropical East Africa 12, pp. 2-14 : 2-6

1. CHENOPODIUM L. ,

Gen. PL, ed. 5, 103 (1754)

Mostly annual or perennial herbs, glabrous, pubescent, glandular or mealy with vesicular hairs. Leaves alternate, mostly petiolate, normally broad. Flowers mostly in cymose clusters (" glomerules") variously arranged,?and? mixed, without bracteoles. Calyx of both sorts of flower normally (3-) 4-5-lobed, unaltered or nearly so in fruit, or sometimes becoming fleshy. Stamens 1-5. Fruits with membranous indehiscent pericarp. Seeds " horizontal " (vertically compressed) or, less commonly, " vertical " (horizontally compressed); testa normally thin, hard and brittle. Embryo annular. Endosperm present.

Weeds of cultivated areas and waste landa around human habitations.

The species here have to be separated from one another with care. Differential vegetative characters, though present, may be indefinite and difficult to portray. The fruits and seeds, however, give for the majority of the species very precise and constant characters. The markings on the testa of the seed, taxonomically very valuable, require the low power of a compound microscope for them to be clearly seen. Special care must be taken,before examining the testa, to remove the thin skin-like pericarp which closely covers it; this can be done either by kneading some fruits between thumb and forefinger, or, if the pericarp is persistent, by scraping it away with needles, using a lens. Until the user of this Flora is familiar with the species, it is better that he tries to name only plants bearing ripe seeds, which fortunately are lavishly produced.

In all the East African species, the flowers in each inflorescence are a mixture of hermaphrodite and female, the former usually occupying the terminal position in a cymule, the latter often opening later. In the following key and descriptions the stamen numbers must be taken to refer to the hermaphrodite flowers only.

Several of our species, especially C. album , G. opulifolium , C. murale and C. ambrosioides , also occur in Europe, and those seriously studying this difficult genus will do well to consult modem works dealing with it there. Hegi, 111. FI. Mittel-Eur. 3 (1910) is recommended for its illustrations; Ascherson & Graebner, Syn, Mitteleur. FI. 5 (1) (1913) for synonymy and an account of the wide ranges of variation of certain species; while Clapham, Tutin & Warburg, FI. Brit. Is. (1952) provides a concise and up-to-date account of the genus in Britain.

Plant more or less mealy, at least on young parts, with grey or whitish vesicular hairs; other sorts of hair and also glands absent; stamens (of hermaphro¬ dite flowers) always 5; seeds always black when ripe, 1 mm. or more in diameter:

Seeds sharply keeled on margin, 1.2-1.5 mm. in diameter; testa marked with very close minute rounded pits (Fig. 2/3); pericarp very difficult to detach from seed; inflorescences always cymose and leafy...... 3. C. murale

Seeds bluntly keeled on margin; testa not marked as above; pericarp readily rubbed or scraped from seed:

Seeds 1-1.5 mm. in diameter; testa marked with radial furrows, and often also with minute roughnesses in between, never closely pitted:

Leaves (except juvenile ones following the cotyledons) distinctly longer than broad, normally by at least 1/2 times; steins often more or less red; branching commonly erect or suberect; testa furrowed, other¬ wise almost smooth (Fig. 1) ... 1. C, album

Leaves (at least median and lower cauline) nearly or quite as broad as long, rather small, up to about 5.4 cm. long; stems rarely red; branching commonly diver¬ gent;testa marked with radial furrows more closely than in (7. album , also with minute roughnesses in between (Fig. 2/2); inflorescences normally very grey-mealy. 2. C. opulifolium

Seeds 1.5-2 mm. in diameter; testa farrowed or pitted:

Leaves below widest point cuneate and normally entire, sometimes broadly cuneate; teeth up to about 10 each side, usually fewer, not acuminate, usually directed upwards; seeds not more than 1.85 mm, in diameter (usually less than 1,75 mm.); testa marked with radial furrows but not pitted (Fig. 1); calyces shed with fruit, sepals not becoming reflexed...., 1. C. album

Leaves below widest point rounded in outline to subtruncate or even subcordat© and distinctly toothed; teeth 7 - 60 each side, usually numerous, acuminate or acute, tending to be directed outwards; seeds 1.5-2 mm. in diameter; testa marked with very close minute sinuose and irregularly branched pits (Fig. 2/4); calyces often per¬ sisting on inflorescence after fruit is shed, their sepals reflexed and with thickened midribs......4. C. fasciculosum

Plant pubescent, and with yellow to amber glands, aromatic, without vesicular hairs; stamens (of hermaphrodite flowers) 1 - 5; seeds black to red-brown when ripe, 0.5-1.25 mm. in diameter:

Inflorescence built up of distinct though sometimes small dichasial cymes in the axils of leaves or bracts, these cymes usually aggregated as though into a spike; seeds black or nearly so when ripe; stamens 1-2; lower and median leaves pinnately divided, at least their lower part; sepals always keeled:

Seeds 0.7-0.8 mm. in diameter; testa marked with very minute shallow contiguous rounded or angular pits (Fig, 2/7); glands between veins on lower surface of leaf, also those on outside of sepals, all sessile (use X 20 lens); leaves pinnately divided throughout each side usually to within 2-3 mm. of midrib.. 7, C. schraderianum

Seeds 0.9-1.1 mm. in diameter; testa marked with slightly impressed sinuoso lines and minor roughnesses (Fig. 2/6); glands between veins on lower surface of leaf,also many of those on outside of sepals, shortly but dis¬ tinctly stalked (use X 20 lens); lower part of leaves pinnately divided, top part toothed but scarcely lobed..... 6. C. procerum

Inflorescence built up of small sessile or subsessile clusters of flowers in the axils of leaves or bracts, flowers not in dichasial cymes; seeds red-brown to blackish when ripe; stamens 1-5; leaves and sepals various:

Sepals each having on its back outside a con¬ spicuous wing-like keel broadening upwards; leaves to 3 cm. long; flowers all in leaf-axils; stamen 1; seeds all " vertical " (see generic description), red-brown, 0.5-0.75 mm. in diameter .... .... 8. C. carinatum

Sepals rounded, not at all keeled on back:

Seeds in each cluster, some " vertical," others " horizontal " (see generic description), 0.5-1.25 mm. in diameter (in African specimens); stamens 4-5; ovary glandular above; stigmas 3-4, long; robust erect plant with paniculate inflorescence... 5. C. ambrosioides

Seeds in each cluster all " vertical " (see generic description), 0-5-0*75 mm. in diameter; stamen 1; ovary not glandular; stigmas 2, short; plant prostrate to ascending, usually slender, with small leaves and axillary flower-clusters not clearly paniculately arranged.... 9. C. pumilio