Bur

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A bur (also spelled burr) is a seed, dry fruit or infructescence that has hooks or teeth. The main function of the bur is to spread the seeds of the bur plant, often through epizoochory. The hooks of the bur are used to latch onto fur or fabric, enabling the bur – which contain seeds – to be transported to another location for dispersal. Another use for the spines and hooks is physical protection against herbivores. Their ability to stick to animals and fabrics has shaped their reputation as bothersome. Some other forms of diaspores, such as the stems of certain species of cactus, also are covered with thorns and may function as burs. Bur-bearing plants, such as Tribulus terrestris and Xanthium species, are often single-stemmed when growing in dense groups, but branch and spread when growing singly. The number of burs per fruit along with the size and shape can vary largely between different bur plants.