Quinoa plant before flowering
Chenopodium quinoa is a dicotyledonous annual plant, usually about 1–2 m (3.3–6.6 ft) high. It has broad, generally powdery, hairy, lobed leaves, normally arranged alternately. The woody central stem is branched or unbranched depending on the variety and may be green, red or purple. The flowering panicles arise from the top of the plant or from leaf axils along the stem. Each panicle has a central axis from which a secondary axis emerges either with flowers (amaranthiform) or bearing a tertiary axis carrying the flowers (glomeruliform). The green hypogynous flowers have a simple perianth and are generally self-fertilizing. The fruits (seeds) are about 2 mm (0.08 in) in diameter and of various colors—from white to red or black, depending on the cultivar.
Chenopodium quinoa is believed to have been domesticated in the Peruvian Andes from wild or weed populations of the same species. There are non-cultivated quinoa plants (Chenopodium quinoa var. melanospermum) that grow in the area it is cultivated; these may either be related to wild predecessors, or they could be descendants of cultivated plants.
Saponins and oxalic acid
In their natural state, the seeds have a coating which contains bitter-tasting saponins, making them unpalatable. Most of the grain sold commercially has been processed to remove this coating. This bitterness has beneficial effects during cultivation, as it deters birds and therefore the plant requires minimal protection. The genetic control of bitterness involves quantitative inheritance. Although lowering the saponin content through selective breeding to produce sweeter, more palatable varieties is complicated by ≈10% cross-pollination, it is a major goal of quinoa breeding programs, which may include genetic engineering.
The toxicity category rating of the saponins in quinoa treats them as mild eye and respiratory irritants and as a low gastrointestinal irritant. In South America, the saponins have many uses, including their use as a detergent for clothing and washing, and as a folk medicine antiseptic for skin injuries.
Additionally, high levels of oxalic acid are in the leaves and stems of all species of the genus Chenopodium, and in the related genera of the family Amaranthaceae. The risks associated with quinoa are minimal, provided it is properly prepared and the leaves are not eaten to excess.