Heliades
Ἡλιάδες
Sisters who wept for their brother until they became poplar trees.
They were Phaethon's sisters, and they wept for four months beside where he fell.
Their feet took root, their bodies were wrapped in bark, and they became poplars — and still the tears did not stop.
Those tears hardened into amber. The Greek word for amber is elektron — the source of the word "electric."
SourcesOvid, Metamorphoses