The lawn in front of my raspberry patch has little white flowers growing in it. They’re very tiny and very short, so the mower doesn’t even get them, but they’re a mystery. Most of the photos I've checked on the Web show distinct petals (like stars or similar), and these flowers form a cup of petals, they’re not separate. It’s not miner’s lettuce (wrong leaf), and it’s not chickweed, although it can be pulled up as easily as chickweed. What are they?