Here is a Canada thistle (Cirsium arvense) seed at 40x magnification. Contrary to the name, it's not native to Canada, but to Europe, North Africa and Asia, but now grows through most of North America. The plant has been used by the Mohegan to treat tuberculosis, and by the Abnaki to treat worms in children. This seed's dimensions are about 0.8 mm wide by 3.4 mm long.
Equipment used: AmScope M150C microscope with Raspberry Pi camera module V2 (8MP).