Beet Pigments: Betalains There are four main classes of plant pigment: chlorophylls, carotenoids, flavonoids and betalains. Chlorophylls and carotenoids are insoluble in water and are found in the organelles of cells. Organelles are the structures in cells that have a particular function, for example, the nucleus, chloroplasts and mitochondria. When organelles are coloured by pigment they are also called chromoplasts. Chlorophylls are blue-green or yellow-green pigments that are mainly found in the chloroplasts. Chlorophylls are the primary light-trapping pigments involved in photosynthesis. Their main role is to absorb light energy and convert it into chemical energy. The carotenoids also trap light energy and act to prevent the degradation of chlorophyll molecules in the chloroplasts. Carotenoid pigments ocur in red, orange, yellow and brown colours. The carotenoids produce many of the colours typical of autumn foliage; floral colours that attract pollinators; and the characteristic colours of many fruits and vegetables. The carotenoids are divided into two subgroups: the carotenes and the xanthophylls. Flavonoids and betalains are water soluble pigments found in vacuoles, spaces within a cell filled with air, water or other liquids, and the cytosol, the semi-fluid part of the cell in which the organelles are suspended. Flavonoids are yellow, orange, red and blue pigments. They are responsible for many of the intense colours in vegetables, flowers and fruits. Flavonoid pigments come in a wide range of colours due to subtle structural variations and differences in concentration. The betalains are a group of nitrogen-containing pigments that are yellow, orange, pink, red and purple in colour. Unlike the other three main classes of plant pigment, betalains have a limited distribution. Most red colouration in plants is due to carotenoids and flavonoids. The red colour of most fruit and vegetables, such as strawberries, grapes and red cabbage, is due to anthocyanins, which are in the flavonoid class of pigments. Betalains are restricted to plants in the order Caryophyllales, and the fungal genus Amanita. In addition to Beta vulgaris (family Chenopodiaceae), betalains have been described from Cactaceae fruits (prickly pear), Amaranth seeds (Amaranthaceae), Bougainvillaea bracts (Nyctaginaceae), and flowers or other plant parts within the Aizoaceae, Basellaceae, Didieraceae, Phytolaccaceae and Portulaceae. Nine of the eleven families within the order Caryophyllales therefore have plants containing betalains. The other two families (Caryophyllaceae and Molluginaceae) have anthocyanins (flavonoids) instead, which probably reflects an early taxonomic division within this plant order. Red beetroot and prickly pear (Opuntia ficus-indica) are the only edible sources of betalains.