Look out for the white, umbrella-like flower heads of lesser water-parsnip along the shallow margins of ditches, ponds, lakes and rivers. When crushed, it does, indeed, smell like parsnip!

Water-plantain is an aquatic plant of shallow water and muddy banks. In bloom over summer, it displays tall branches of loosely clustered, pale lilac flowers.

Water-cress has become so popular as a salad addition that it is now cultivated on a wide scale. In the wild, it grows in shallow, fast-flowing streams and is an indicator of clean water.

Water-soldier grows submerged in ponds and open water, and pops up over summer, looking like the top of a pineapple! This rare plant displays white flowers and shelters many aquatic insects.

Found in ponds and marshes, the fragile look of the common water-measurer belies its fierce nature. A predator of small insects, it uses the vibrations of the water's surface to locate its…