4. Chenopodium L. (goosefoot, pigweed)

Plants usually annual (perennial elsewhere), the roots not tuberous-thickened. Stems prostrate to erect, not succulent, not appearing jointed, few- to much-branched, glabrous, glandular-hairy (sometimes also with nonglandular hairs), or sparsely to moderately mealy. Leaves alternate, well developed, not or only slightly succulent, petiolate or nearly sessile. Leaf blades linear to ovate or triangular, sometimes with a pair of spreading basal lobes, flattened in cross-section, not clasping the stem, rounded or narrowed to a sharply pointed tip, the margins entire, wavy, toothed, or lobed, the surfaces glabrous, glandular- and/or nonglandular-hairy, or sparsely to densely mealy. Inflorescences axillary and/or terminal, consisting of small flower clusters, these often appearing as interrupted spikes or panicles (occasionally a few nodes then with solitary flowers), the flowers not sunken into the axis. Flowers perfect (rarely a few pistillate flowers also present). Bracts absent or rarely 3 and minute. Calyx deeply 5-lobed, the lobes persistent at fruiting and all or partially enclosing the fruit, not winged, spaced evenly around the flower, often keeled or with a low, vertical ridge, rarely fleshy (in C. capitatum). Stamens 3–5 (usually only 1 in C. pumilio). Ovary superior. Styles 2 or 3, short, sometimes fused toward base, the stigmas 1 per style, linear or capitate. Fruits elliptic to circular in cross-section, depressed-globose to ovate in outline, somewhat flattened laterally or vertically, indehiscent or irregularly dehiscent, the wall thin and papery to membranous. Seed adhering loosely or tightly to the fruit wall, positioned vertically or horizontally, the surface smooth or less commonly roughened or with a low network of fine, rounded ridges, dark brown to black, shiny or less commonly dull, the coiled embryo usually apparent. About 150 species, nearly worldwide.

Immature specimens of Chenopodium often are difficult or impossible to identify and should not be collected. Fruits will, however, sometimes mature in the plant press while samples are drying. For large plants, it may be important to note the morphology of the larger, lower leaves when collecting samples for later determination. The adherence of the thin, membranous to papery wall of the fruit to the seed usually can be tested by rubbing a few mature fruits lightly between thumb and forefinger. In species with loosely adhering fruit walls this action will suffice to remove them, but in species with tightly adhering walls it will serve only to strip away the calyx.

Some species of Chenopodium, notably C. album, are cooked and eaten as a spinach substitute or (in combination with Amaranthus, Lactuca, Sonchus, Rumex, etc.) as field greens in the springtime when tender young growth is present (Steyermark, 1963). Native Americans also ground the seeds for flour (Moerman, 1998).

Crawford and Wilson (1986) included Missouri in their synopsis of the range of the western species C. atrovirens Rydb. However, in response to a query during the present research, Daniel J. Crawford (then of Ohio State University) indicated that this was a typographical error and was intended to read MT (Montana), rather than MO (Missouri).

Chenopodium bonus-henricus L. (good King Henry) is a perennial herb that is cultivated occasionally for its spinachlike leaves. It may be encountered in the future as an escape in Missouri. Aside from the thick, woody rootstock, this species may be recognized easily by the triangular leaves often with a pair of spreading basal lobes (similar in appearance to those of some Missouri species of Atriplex) and the oblong calyx lobes only partially enclosing the fruit, with the tips truncate to rounded or broadly angled and usually somewhat irregular margins.