Comments for the name Althea

Althea, from Greek Ἀλθεία, was Meleager's mother's name and is also the Latin scientific name of the marshmallow plant, Althaea officinalis. In ancient Greek, ἀλθεία could also designate the mallow (Malva).

The name comes from the root ἀλθαι-, "heal", which gave the verb ἀλθαίνω. Ἀλθαία merely means "healing substance", which refers to the way this medical plant was used during Antiquity.

Source: Dictionnaire étymologique de la langue grecque by Pierre Chantraine.

This name comes from the Greek for truth.

I believe you're confusing this name with Alethea. Althea does not come actually from the Greek word for truth, but Alethea does.