These two, also misidentified by me:
Before flowering, the leaves are nearly identical, with subtle differences:
- The Cotula is more decumbrent with the Lepidium more prostrate
- The Cotula may have some hairs on the stem with the Lepidium more glabbrous
- The Cotula has an annual, clump-of-hairs root with the Lepidium having a taproot
It also doesn’t help that they sprout and grow during the same season.
The most reliable way to tell them apart is to crush the leaves. The Cotula has no smell but the Lepidium has a strong wasabi/garlic smell.