Oxalis corniculata spreads by rhizomes, stolons, and seed — and the seeds are launched forcefully up to 16 feet from their cylindrical pods, a dispersal trick borrowed from the impatiens playbook. The bright yellow flowers are small but abundant, sitting above heart-shaped trifoliate leaves that close up at night and unfurl again in the morning. It tolerates poor soils and grows year-round in warm climates, making it a formidable presence in container nurseries, lawns, and garden beds alike.

Management depends on catching it before seed set, since preemergence herbicides handle the seedlings well but do little once rhizomes are established. In propagation areas especially, sanitation is critical: inspect incoming plant material carefully, and don't let colonies flower. The plant does attract bees to its modest yellow blooms, which is worth noting. In zones 4 to 8, it behaves like an annual in colder regions and a perennial in milder ones.