Thaleia was a nymph, the child of Hephaestus. She is also given as an anthropomorphic secondary deity of plant life and shoots, possibly as the culmination of the transmission of knowledge on volcanic ash's use as a fertiliser, characteristic of ancient viticulture in volcanic soils such as those of the islands of Thera and Santorini.
Zeus seized this Thaleia whilst he was in the form of an eagle, as he did with Aegina, Leto and Ganymede. He then made love to her near the river Symethe on Sicily and then buried her in the ground to avoid Hera's jealousy. Her twin children, the Palici, were thus born from the earth, though other authors make the Palici the sons of Hephaestus.
Her name meant, "the Joyous, the Flourishing", from θάλλειν / thállein, "to flourish, to be green".
The tradition surrounding her is confused, but she is probably confused with the Muse, Grace or Nereid of the same name.