If you are about to plant your spring garden, you may be looking at the weeds that have come up during winter and feeling a bit overwhelmed. One weed in particular, drives local gardeners crazy. We call it Bermuda buttercup, or Cape oxalis, yellow oxalis, or sour clover. It's scientific name is Oxalis pes-caprae, showing that it is a relative of our native redwood sorrel, which is Oxalis oregana. The weedy oxalis is, however, not native to California, but to the Cape region of South Africa.
This weed is dormant in summer, then emerges from the ground in the fall, when it looks kind of nice covering the ground with its trefoil leaves that remind us of clover. But by the time that the plant has bloomed, with its rather pretty, yellow, funnelform flowers, we realize that it has taken over whole swaths of the garden, and that spring bulbs and other perennial flowers, not to mention tender seedlings, are going to have a tough time competing. (And, by the way, no this plant is not a legume, like clover, that adds nitrogen to the soil. The leaf resemblence is superficial only.)
This weed reproduces from many small teardrop shaped bulbs. If it is pulled when it is young, say, before it flowers, you may be able to deplete the bulbs so they have less energy to regrow, but hand eradication usually requires a combination of pulling and digging to remove bulblets. As you pull out large oxalis plants this spring, resolve to act sooner next year, in the fall, so that the plants can't store up food for next year.
The only good news, at least so far, is that no one has been able to proove that those yellow flowers ripen seed. In fact, a member of the California Native Plant Society has put out a $100 reward for anyone who can proove the plant reproduces by seeds. Let me know if you have proof, and I will tell you who to contact. In the meantime, hope your weeding goes well!