I love buttercups. The meadow variety has taken over our boggy lawn but so have soft and compact rushes, star sedges and sharp-flowered rushes. Yellow flags are joining in, red clover, yellow pimpernel, lesser celandine, lady's smock, sorrel, dock.... The list goes on.
Most recent 'invader' (or is it gentle immigrant?) is Libertia grandiflora. That can take over too if it wants.
I haven't yet counted the 'invasive' species in my garden but I reckon it could be at least a quarter of them.
I've just been into the field that's next to us to pick a grass sample to identify and had the loveliest experience. On the way up to the top of the garden I saw Meadow Brown butterflies and Ringlets, then, as I stepped out into the field, several Ringlets rose from the tall grasses and 'weeds' at almost every step. It was wonderful!