Trefoil

Lesser Trefoil (Trifolium dubium)

Right now, the edges of our driveway — and anywhere else the grass is short or non-existent — are covered with the tiny trefoil leaves and little yellow flowers of Lesser Trefoil (Trifolium dubium). Also known as Yellow Suckling Clover, this low-growing annual is a member of the pea family, and has the typical "pea flower",  just on a very small scale. The whole flower head, which consists of a dozen or more flowers, measures a mere 5mm (1/4-inch) across. The plant tolerates a wide range of conditions, but is especially common on lighter, sandy, nutrient-poor soils like we have here. Its hard little seeds are remarkably persistent, with some successfully germinating even 20 years after they were produced. Sadly, just about every source on the internet talks about how to eliminate it from lawns, as if having it there might be a problem (as I suppose it would be if you wanted a putting green instead of some biodiversity). Given that the plant helps to fix nitrogen into the soil, thereby improving it, you'd think people might be willing to tolerate a few plants!

Though native to Europe, Lesser Trefoil has been widely introduced across the world, generally as a contaminant in crop seeds. It's a common and widespread species across Britain. It's similar in appearance to Hop Trefoil, but has smaller flower heads with fewer flowers, and its flowers don't swell as they go to seed, like those of Hop Trefoil do. It blooms from May through August on drier soils, and through October in moister places. The flowers are insect-pollinated, and bees in particular are attracted to them — reason enough to tolerate multiple patches, in our opinion.