I'll bet this drain hasn't been cleared out in a wee while!
On closer inspection I could identify at least two species of ferns, including that old favourite European Hart's Tongue Scolopendrium phyllitis. A leaflet from the pest species that's locally called Mexican Daisy - an unwanted, but very pretty weed - can be seen in the centre of the drain. And a tiny bit of Herb Robert leaf can be seen top left.
