It's the season for slender speedwell Veronica filiformis, a Victorian rockery favourite that first hopped over the garden wall in 1838, but didn't really begin its rampage until the late 1920s. It has been on the run ever since, invading lawns everywhere. The New Atlas of the British and Irish Flora confirms that it is still spreading.
The remarkable thing about this little colonist is that it almost never produces seeds but has spread the length and breadth of the country via vegetative propagation, thanks to its creeping stolons that thread their way through the grass, lawnmowers and the distribution network created by wholesale and retail horticulture that introduced it to gardens throughout the nation in the early years after its introduction from Turkey in 1808.
Once established in lawns, slender speedwell was distributed in lawn turf and then propagated by lawnmowers. Each pass of the mower takes hundreds of cuttings and many of them will quickly root. One plant can soon become a blue carpet.
As with daisies, it thrives in short grass - let the lawn grow a bit and it will struggle to compete. It's our national fetish for well-mown lawns and their establishment from turf that's already infested, rather than growing a lawn from seed, that has ensured its survival and spread.