Phaëthon's sisters, the Heliades, turned into poplars.

The daughters of Helios, the sisters of Phaethon. They were turned into poplar trees.

Phaëthon was the son of the Sun, Helios, and Clymene. His sisters were the Heliades.

Phaëthon's sisters were the Heliades. When they were mourning for him at the riverbank of Eridanus, they were turned into poplars.

Yes, the Heliades, supposedly named:

Merope, Helie, Aegle, Lampetia, Phoebe, Aetherie, Dioxippe.

or

Lampetia, Phaethousa, Aigle

or

Lampetia, Phaethousa, Phoibe