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The species are mostly herbaceous perennial plants 0.3–1.5 m (0.98–4.92 ft) tall, but some are annual plants and a few are shrubs up to 3 m (9.8 ft) tall. An exception is the chamis de monte (Lupinus jaimehintoniana) of Oaxaca in Mexico, which is a tree up to 8 m (26 ft) tall. Lupins have soft green to grey-green leaves which may be coated in silvery hairs, often densely so. The leaf blades are usually palmately divided into five to 28 leaflets, or reduced to a single leaflet in a few species of the southeastern United States. The flowers are produced in dense or open whorls on an erect spike, each flower 1–2 cm long. The pea-like flowers have an upper standard, or banner, two lateral wings, and two lower petals fused into a keel. The flower shape has inspired common names such as bluebonnets and quaker bonnets. The fruit is a pod containing several seeds that weight in average 24,8 mg each (n=50).
Many annual species of lupins are used in agriculture and most of them have Mediterranean origin. While originally cultivated as a green manure or forage, lupins are increasingly grown for their seeds, which can be used as an alternative to soybeans. Sweet (low alkaloid) lupins are highly regarded as a stock feed, particularly for ruminants, but also for pigs and poultry and more recently as an ingredient in aqua-feeds. The market for lupin seeds for human food is currently small, but researchers believe it has great potential. Lupin seeds are considered "superior" to soybeans in certain applications and evidence is increasing for their potential health benefits. They contain similar protein to soybean, but less fat. As a food source, they are gluten-free and high in dietary fiber, amino acids, and antioxidants, and they are considered to be prebiotic. About 85% of the world's lupin seeds are grown in Western Australia. Three Mediterranean species of lupin, blue (narrow-leafed) lupin, white lupin, and yellow lupin, are widely cultivated for livestock and poultry feed. Like other legumes, they can fix nitrogen from the atmosphere into ammonia via a rhizobium–root nodule symbiosis, fertilizing the soil for other plants. This adaption allows lupins to be tolerant of infertile soils and capable of pioneering change in barren and poor-quality soils. The genus Lupinus is nodulated by Bradyrhizobium soil bacteria.