Amaranth Family (Amaranthaceae)
The amaranth (or pigweed) family is a large group of dicotyledonous flowering plants known to botanists as the Amaranthaceae. It is a relatively large family, having about 65 genera and 900 species. The species in this family are mostly annual or perennial herbs, although a few species are shrubs or small trees. Botanists divide Amaranthaceae into two subfamilies: the Amaranthoideae and the Gomphrenoideae, based on certain morphological characteristics of their flowers.
The flowers of most species in the Amaranthaceae are bisexual (or monoecious), meaning they have both male and female reproductive organs. In all species, the flowers are small and have radial symmetry. The flowers of most species arise in a dense inflorescence, or flower cluster, with each flower of the inflorescence subtended by one or more small red bracts (modified leaves). The small red bracts remain present as the flower matures into a fruit. The flowers of most species produce nectar and are insect-pollinated. An exception is Amaranthus, a genus with about 50 species, whose flowers are wind pollinated and do not make nectar. All species have simple, non-compound leaves.
Many species in Amaranthaceae have red inflorescences, fruits, and vegetative parts, due to the presence of betalain pigments. Betalains are a class of nitrogen-containing pigments, which only occur in 10 evolutionarily related plant families, known as the Centrospermae. Interestingly, none of the species with betalain pigments also have flavonoid pigments. Flavonoids and betalains can be similar in color, even though they have different chemical structures.
Most of the 900 species of Amaranthaceae are native to tropical and subtropical regions of Africa, Central America, and South America. The number of Amaranthaceae species declines as one approaches the northern and southern temperate zones. There are about 100 species of this family in North America. Many species of Amaranthaceae are considered weeds, since they invade disturbed areas, such as agricultural fields and roadsides.
Several species in the Amaranthaceae family are used by humans. Some species are important horticultural plants, such as Amaranthus caudatus, commonly known as "love-lies-bleeding." The seeds of several species of the Amaranthus genus were eaten by indigenous peoples of North and South America, and were cultivated over 5,000 years ago in the Tehuacan region of modern-day Mexico. Grain amaranths are still grown throughout Central America and Mexico, and also as a minor cash crop in the United States. Many health food stores currently sell amaranth grain, a flour-like substance made by grinding amaranth seeds. Amaranth grain can be used with wheat to make bread, or can be cooked with water to make a side dish.