On numerous occasions, I have walked past a few diminutive specimens of this plant growing in the woods behind my house. Never seeing it in flower, I didn't take particular note, just assuming it was a stunted holly. Had I been paying closer attention, the compound leaves would have been a dead give away. However, in my defense, the plants in question are all very small, with just one leaf, and well off the trails I typically follow.
Today SodaBoy and I walked up to the quarry, and hiked the rim trail all the way around. We stopped for a break at the highest point of the cliffs on the northeast end. Growing not far off the trail, I saw these pretty little yellow flowers:
It turns out the plant is not a holly, but Mahonia aquifolium (also known as Berberis aquifolium). Native to the Pacific northwest, holly-leaved barberry is the state flower of Oregon, and is also known by the common name of Oregon-grape. The plant is collected from the wild for medicinal use, harvested to the point where there is some concern over the long-term viability of the species in its native range. It is also used in landscaping and is known to be adventive, especially in the east, where it is not native.
The species is not documented from my county, and in fact, is only known from one county in my state, quite a long distance from here. The population I saw today was small enough that were this a native plant, I absolutely would not collect a voucher specimen. The plants behind my house are hardly thriving either. I do not think this species is a big threat in my area at this time. But who knows what the future will bring? This could be important information.
Unfortunately, the quarry rim trail is not a hike that can be managed in the evening after work. Our spring has been late but hot, so accelerated that plants I saw just starting to flower last weekend are in fruit already. If this trend continues, I'll have to collect an Oregon-grape voucher specimen later in the season. At least then I will be able to see the "grapes" for myself.
Sources: PLANTS Database, NatureServe, Flora of North America.