Go down to the Nevern estuary, slip off your shoes, splurge over the mud. Your toes are already rejoicing. "We've come to a health farm," they sing in happy chorus. You're heading towards a bed of glasswort, at last a vegetable not festooned with slugs. Originally it was used to make glass. If you burn a pile of it you horrify epicures to create a sort of carbonate of soda, which mixed with sand will give you glass.

William Turner, in his 1568 A New Herball, called it glaswede. When people started to eat it, the name marsh samphire became popular. It has a distinctive peppery taste and fibrous texture. Here it is only washed twice a day by salt water, so its salty flavour is not overpowering. You can use it in salads, or cook it like asparagus and gently tease the succulent flesh from the stems. It's an annual, but the flowers need to be searched for as they are so small. They nestle at the joints of the stalks - as edible as the rest of it.

The name samphire comes from the French "herbe de St Pierre" originally describing the rock samphire, Crithmum maritimum. This grows on our cliffs, an umbellifer with linear fleshy leaves. It is King Lear's samphire, but I've never meddled with the dreadful trade of picking it. Another samphire is Inula crithmoides, the golden samphire, which has a daisy flower.

Another type of inula is Nicholas Culpeper's "robust and stately plant", the elecampane, Inula helenium, confirmed by modern medicine as holding a root helpful against chest infections. In some places it is called wild sunflower, but nowadays you can walk far enough without spotting it - apart from old cottage gardens, where its generous fecundity quickly fills the ground and delights, or daunts, the passerby. Long ago it came here from Asia for its medical qualities, and continued to America. This does not presage plant globalisation, simply recognition of medicinal properties. Certainly our bees and butterflies respond well to this eastern immigrant. The glasswort is an old island plant and looks it.