I found this seedling in my garden two years ago and potted it up thinking I'd found a Mahonia aquifolium of which I can always use more of. I figured the single leaves were a juvenile characteristic and it would revert to compound leaves as it got older. After a fertilizer induced growth spurt this summer, I'm beginning to rethink the id. It was found growing under a Thuja, within 2' of an small Mahonia aquifolium that I don't recall every bearing fruit. There are other Mahonia aquifolium close by as well as Berberis thunbergii within 100'. No other Berberis (no vulgaris nearby & I think my B. julianae experiment never managed to flower before dying) and my M. bealei had not flowered for the first time yet. What is apparent.... - leaves are single with spines but are not stiff like Mahonia - spines at leaf base (never seen that on Mahonia) - senescing leaves turn yellow (not evergreen) and break off at leaf stalk first, leaving leaf stalk on stem (similar to Mahonia) Any ideas? It's not just plain old B. vulgaris, is it?