prostrate vervain (Verbena bracteata)
non-native
pictures taken in june
surprisingly difficult to find any information at all about prostrate vervain! none of my books have it; i'm not sure if it's just unremarkable, a recent introduction to the area, or what.
despite the name, you may note from the pictures that prostrate vervain is not that prostrate; it does spread along the ground, but it also likes to grow upright, especially the strange flower stalks. the flowers are pretty, but very small! apparently despite their itty-bitty size, they are visited by some butterflies.
this type of vervain is native to, apparently, the entire continent except the northmost parts of canada, the southernmost parts of mexico, and the east coast! it's just introduced here. it's also a classic colonizer plant which is happy to live in disturbed poor-quality soil in large quantities, then backs off politely when other plants come.