After the Prachetas finished their meditation on the bottom of a lake they realized that the earth was overgrown with wild trees. They burned the trees who in return asked Lord Brahma to help them. Therefore Brahma appeared in front of the Prachetas to offer them Marisha, the daughter of the trees, as their wife. The Prachetas accepted the offer.
(Srimad-Bhagavatam 4.30.12-13)