Begonia rex, the king begonia, fancy-leaf begonia, or painted-leaf begonia is a species of flowering plant in the family Begoniaceae. It's a rhizomatous begonia first brought to England from Assam, and documented in 1857.

It is native to the East Himalayas, found from southern Bhutan to northern Myanmar, and has been introduced to Bangladesh, Cuba, the Dominican Republic, and Haiti.

These plants are noted for their dark leaves with prominent silvery grey bands, and are usually grown for their foliage, not flowers. When this species was introduced into cultivation, it became popular as a houseplant. Hybrids began to appear with varying leaf patterns as Rex begonias hybridize quite freely.

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