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Spartina

Spartina

The sharp-leaved large grass in the middle of the picture is Spartina. It can grow up to a metre high and is well known as a pioneer species of salt marshes. It can tolerate long periods of immersion and can colonise and stabilise areas of bare mud. It has deep roots for anchorage which also consolidate the mud. It has fine fibrous shallow roots for absorbing water and nutrients. If you look carefully at the picture you should be able to see salt crystals on the leaves. These have been excreted by the plant's salt glands.

On the salt marsh the concentration of salts in the soil solution is high. This means that water will have a natural tendency to leave the plant by osmosis. Salt marsh plants have adaptations to deal with this. Spartina has salt glands, a thick cuticle and its stomata are located in deep grooves, this will reduce transpiration and conserve water.

Less obviously, it photosynthesises using the C4 pathway. Without going into detail this allows it to absorb carbon dioxide with partially open stomata or at night when transpiration is low and store it chemically. It can then photosynthesise during the day with its stomata only partially open (thus conserving water). Most plants in temperate climates use the C3 pathway which is chemically more efficient but you have to have your stomata fully open (to absorb carbon dioxide) during photosynthesis, so you lose more water by transpiration. The majority of C4 plants live in tropical climes where photosynthesis is so fast that carbon dioxide becomes limiting and water efficiency is important.

Long ago there was but one species of Spartina in the UK. This was known as Spartina maritima. Then, in the 1820s someone discovered another species of Spartina called Spartina alterniflora. The newcomer originated in North America and because it was first found in Southampton Water it was assumed it had been introduced via shipping.

The American Spartina then crossed with the native Spartina to make a hybrid form. This was called Spartina X townsendii. This version was infertile but could spread vegetatively.

In an astonishing bout of natural genetic engineering Spartina X townsendii doubled its chromosome number. The resulting species was called Spartina anglica. It was fertile and successful possessing what people sometimes call hybrid vigour. It spread to such an extent that people began to worry about it colonising mud flats and depriving wading birds and fish of food in the form of the worms and molluscs that lived there. In Milford Haven the vigorous hybrid was introduced deliberately during World War Two. The plant in the picture is on The Gann salt marsh near Dale. Spartina anglica was first found here in 1952.

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