Rudraksha (also Rudraksh; Sanskrit: rudrākṣa ("Rudra's eyes") is a large evergreen broad-leaved tree whose seed is traditionally used for prayer beads in Hinduism. The seed is borne by several species of Elaeocarpus, with E. ganitrus being the principal species used in the making of a bead chain or mala. Rudraksha is a Sanskrit compound consisting of the name Rudra ("Shiva") and akṣha ("eyes"). The specific epithet ganitrus is possibly taken from ganitri, the name for this species in Sundanese and Malay.
Rudraksha grows in the area from the Gangetic Plain in foothills of the Himalayas to South-East Asia, Indonesia, New Guinea to Australia, Guam, and Hawaii. Rudraksha seeds are covered by an outer shell of blue color when fully ripe, and for this reason are also known as blueberry beads. The blue colour is derived not from pigment but is structural. It is an evergreen tree that grows quickly. Rudraksha Tree starts bearing fruit in three to four years. As the tree matures, the roots buttress rising up narrowly near the trunk and radiating out along the surface of the ground.
Religious use 
Rudraksha beads are the material from which malas (108 beads in number) are made. The term is used both for the berries themselves and as a term for the type of mālā made from them. In this sense, a rudraksha is a rosary, used for repetitive prayer (japa), a common aid to worship in Hinduism. Rudraksha is also used for treatment of various diseases in traditional Indian medicine.
The seeds show variation in the number of grooves on their surface, and are classified on the basis of the number of divisions that they have. Different qualities are attributed to the rudraksha based on the number of grooves, or 'faces' that it has. A common type has five divisions, and these are considered to be symbolic of the five faces of Shiva. It can only be worn with red string or a gold chain.
Rudraksha Mala has been used by Hindus (as well as Sikhs and Buddhists) as rosary at least from the 10th century  onwards for meditation purposes and to sanctify the mind, body and soul. The word Rudraksha is derived from Rudra (Shiva—the Hindu God of all living creatures) and aksha (eyes). One Hindu legend says that once Lord Shiva opened His eyes after a long period yogic meditation, because of extreme fulfillment He shed out a tear. This single tear from Shiva’s eye grew into the Rudraksha tree. Rudraksha fruit is blue in color but turns black when dried. The central hard Rudraksha uni-seed may have 1 to 21 faces.
See also 
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- The translation of rudrākṣa as "Rudra's eyes" and definition as berries of Elaeocarpus ganitrus see: Stutley, p. 119.
- Stutley, M. (1985). The Illustrated Dictionary of Hindu Iconography. New Delhi, India: Munshiram Manoharlal Publishers. ISBN 81-215-1087-2.
- Koul, M. K. (2001-05-13). "Bond with the beads". Spectrum. India: The Tribune.
- Lee, D. W. (1991). "Ultrastructural Basis and Function of Iridescent Blue Color of Fruits in Elaeocarpus". Nature 349 (6306): 260−262. doi:10.1038/349260a0.
- For use both to refer to the beads and to a mālā see: Apte, p. 804.
- Das, Subhamoy. "The Holy Rudraksha: Super Seed".
- For the five-division type as signifying Shiva's five faces and terminology pañcānana, see: Stutley, p. 119.
- Seetha, K. N. (2008). Power of Rudraksha (4th ed.). Mumbai, India: Jaico Publishing House. ISBN 978-81-7992-844-8.
- Laatsch, M. (2010). Rudraksha. Die Perlen der shivaitischen Gebetsschnur in altertümlichen und modernen Quellen. Munich: Akademische Verlagsgemeinschaft München. ISBN 978-3-89975-411-7.