Q: A plant about a foot tall with clover-like leaves and yellow, conical flowers that close at night just appeared in my garden. Is it something I'd want to keep?

A: This is Oxalis pes-caprae (Bermuda buttercup, sour grass), a South African native that has naturalized in California. Some people love it, and others do not. It goes completely dormant in early summer and re-emerges in winter. It produces large quantities of small bulbs making it hard to get rid of completely once established. It can be pretty invasive so if it appears where it might smother other small plants as it spreads, dig it out as soon as you see it. If it volunteers in an area where that is not a problem, you might decide to leave it.