I've just given our lawns their first haircut of the season but was surprised to find that, despite two or three runs of the mower over them, many dandelions (no, I don't use a broad-leaved weed-killer on them!) were reluctant to be beheaded. Normally the dandelion flower-stalk is 5 or 6 inches long, but this year many were less than 1 inch, so the flower heads were down in amongst the grass. Perhaps the dandelion is evolving to be mower-resistant ?