Two Trees of Valinor

The Two Trees of Valinor were, well, two trees. That grew in Valinor.

They weren't just any trees, though. They were shiny. Before the sun and moon were created, the Trees were the primary source of light in Valinor. (Middle-Earth didn't have any light besides stars.) The Trees were sung into existence by the Vala Yavanna.

Telperion was the "male" tree. It gave off a silver glow and had dark leaves that were silver on one side.

Laurelin was the "female" tree. It gave off a golden glow and had gold-trimmed leaves.

The Elf lord Fëanor captured some of the light of the Trees in his masterpieces, the Silmarils.

Melkor, being a jealous sort of person, hated everything that had to do with Valinor, including the Trees. He enlisted Ungoliant, the giant spider, and with her help drained the Two Trees of their light, killing them and plunging Valinor into darkness. Yavanna claimed that she could heal the Trees if she used the light in the Silmarils, but Feanor wasn't too keen on breaking his precious gems, and Melkor had stolen them anyway. Yavanna sang to the dead trees, hoping to revive them, and the Vala Nienna watered them with her tears, but it was no use. They managed to coax a single white blossom from Telperion, and a single golden fruit from Laurelin. These were placed in the sky to serve as light sources for all of Arda, with the flower becoming the moon and the fruit becoming the sun. This is why the sun is often referred to as "she" and the moon as "he" in The Lord of the Rings.