Rig Veda Book 10 Hymn 97 is dedicated to the herbs and I am sharing a part of it here:
HERBS that sprang up in time of old, three ages earlier than the Gods,— Of these, whose hue is brown, will I declare the hundred powers and seven.
Ye, Mothers, have a hundred homes, yea, and a thousand are your growths. Do ye who have a thousand powers free this my patient from disease.
Do any commentaries describe if the hymn is dedicated to any specific herbs or to all of them in general? My specific question is regarding the highlighted portion and I want to know if any commentary explains what it means for the herbs that are brown in color to have emerged three ages before the gods?