|Male Meadow Rue|
|Creeping or Shore Buttercup Ranunculus cymbalaria|
Wikipedia has Thalia as named after Johannes Thal, a German Botanist. But Peter Bernhart in his entertaining Gods and Goddesses in the Garden, considers Thalia as a bit of Linnaean fun, honouring both Thal and yet another Greek Thalia (Θαλία): the Grace of festivities and luxuriant banquets. Given the abundance of flowers and the rather greyish foliage characteristic of Meadow Rues, I think I'll go with the Muse.