To my knowledge, oregon grape (Mahonia aquifolium) is purportedly an evergreen shrub? Deciduous broadleaf plants lose their leaves in autumn usually and before that as the leaves die they oxidize and turn shades of yellow and red as carotenoids and anthocyanins are expressed.
For what reason does M. aquifolium turns red in the fall given that they DON'T drop their leaves? Does it somehow benefit the plant? Is it because oregon grape's ancestor used to drop leaves?