The Red acacia, known also as the shittah tree (the source of shittim wood), is a thorny, 610 m (2030ft) high tree with a pale greenish or reddish bark. At the base of the 310cm (14in) feathery leaves there are two straight, light grey thorns, growing to 720cm (38in) long. The blossoms are displayed in round, bright yellow clusters approximately in 1.5cm (0.5in) diameter. In Acacia seyal var. fistula, which is more common on heavy clay soils, some of the thorns are swollen and house symbiotic ants. It often grows in damp valleys.