The most obvious thing people think about in relation to pond plants is usually the flowers - water lilies reflected in the water, stately bullrushes or yellow irises growing along the bank. But there’s much more to plants than meets the eye. From the point of view of the creatures which depend on ponds there’s a whole network of plants, above and below the surface, which are of vital importance to them for food and shelter.
These plants can be split roughly into four groups depending on the part of the pond in which they grow: those which are submerged; those with floating-leaves; those emerging from shallow water; and those on the margins. A balance between all these types ensures a healthy pond with plenty of wildlife.
Submerged plants are adapted to grow entirely below the surface, some of them not even rooted. They maintain oxygen levels in the water and provide shelter for invertebrates in the deeper parts of the pond. Examples are the native hornworts, which actually flower under water; water-milfoils, and water crowfoot, which has delicate white flowers on the surface of the water.
One particularly unusual and uncommon submerged plant is Bladderwort which occurs in a few sites in Herefordshire. It is carnivorous, bearing small bladders which suck in & trap small creatures. Attractive yellow flowers appear above the surface.
Plants with floating-leaves are rooted in the mud at the bottom of the pond but their broad leaves cover the water surface, cutting out light and so reducing the growth of algae. The leaves also provide cover for invertebrates and amphibians. Lift a lily leaf in early summer and you’re likely to find a newt sheltering beneath. Common plants in this group are broadleaved pondweed, amphibious bistort and of course, water-lilies, the native ones being the vigorous White water-lily and the globe shaped Yellow water-lily.
There are also a few free floating plants in this group like Frogbit (see image on left) which has small lily-shaped leaves and white flowers; and the duckweeds which can completely cover the surface of nutrient rich ponds.
Emergent plants have their roots in water and can grow out into the pond, sometimes completely taking over shallow ponds. Tall emergents like Branched Bur-reed and Reedmace (often called bulrush) are particularly invasive, but provide protection for nesting moorhens and places for dragonfly nymphs to emerge from the water. On windy days numerous damselflies can be found taking shelter among the tall stems.
Bogbean - an emergent pond plant Photo P.King
Marginal plants grow in the marshy areas around the pond and out into the water. Many pond animals live in dense vegetation in very shallow water, often only a few centimetres deep, so the low growing plants, rushes and grasses around the edges of the pond forming a tangled network of stems and roots are very important for wildlife. Great Crested Newts lay their eggs on flat leaves like Water Forget-me-not, Water Parsnip or Flote Grass. The mauve flowers of Water Mint attract bees and butterflies.
Continuing outwards from the margins of the pond are plants of damp ground and marshy areas. Here there are many with colourful flowers, like Marsh Marigold, Ragged Robin (see image on left), Purple Loosestrife (image at head of page), and Hemp Agrimony, whose large flat pinkish flowers are irresistible to bees and butterflies.
As well as these native plants which have adapted to life in British ponds over thousands of years, there are a number of vigorous introduced species which have escaped into the countryside from garden ponds and aquaria and now pose a serious threat to our plants and wildlife. Many form dense mats of vegetation which smother native plants, deplete oxygen levels in the water and create a poor environment for amphibians, fish and invertebrates.
Those which particularly need to be watched out for are:
- New Zealand Pigmyweed (Crassula helmsii or Tillaea recurva as it’s sometimes known).
- Parrot’s Feather
- Water Fern
- American Pennywort
Invasive Plant images © Centre for Aquatic Plant Management - www.capm.org.uk.
Plants for wildlife
A balance between the types of plant listed creates a habitat which will attract wildlife, but some plants are particularly important for certain species.
Dragonflies need plenty of submerged plants for their developing larvae, while their emerging larvae need tall emergent plants, which also provide sheltered places for perching and roosting. A variety of plants is also required for egg laying, some dragonflies and damselflies laying their eggs into the stems of marginal vegetation, others into floating or submerged plants. Red-eyed damselflies spend long periods perched on the leaves of water-lilies.
Moorhens and coots build their nests within the protection of tall rushes and reeds, which also shelter the chicks from predators like foxes.
There are even moths, the Chinamark moths, whose caterpillars live under water, feeding on pondweeds and duckweeds.
So it is the variety and balance of plant species which is so important.