Introduced plants and animals are not a major factor in driving changes in British and Irish wildlife, but they are certainly an additional factor in the survival of some species, for example the effects of grey squirrels on the survival of red squirrels, or mink on water vole numbers. In this chapter we will consider recent introductions, either intentional or accidental, by humans, and also species that have arrived recently of their own accord. Let us start with the plants.
Plants introduced to our flora before 1500 are termed archaeophytes, and those introduced later, neophytes. Both include many species which adorn our flora, although a few have become ‘problem’ plants, especially some neophytes. Many archaeophytes are herbs that were introduced for medicinal or culinary use, but they also include numerous cornfield weeds such as corn buttercup (Ranunculus arvensis), pheasant’s-eye (Adonis annua), charlock (Sinapis arvensis) and common poppy (Papaver rhoeas). Alexanders (Smyrnium olusatrum), now so common along coastal roadsides in Norfolk and elsewhere, was brought by the Romans, probably as a spring vegetable. Its leaves are amongst the earliest foliage of the year. So too horse-radish (Armoracia rusticana), now common on roadsides, which even in medieval times was dug to provide sauces with the special flavour of its grated roots, and greater celandine (Chelidonium majus). (This latter, no relative of the lesser celandine (Ranunculis ficaria) which is in the buttercup family, while greater celandine is actually in the poppy family, and betrays this by the milky latex that oozes from the cut stems.) It used to be acclaimed in herbal medicine for the efficacy of its latex as a wart remover. Some herbs such as hemlock (Conium maculatum), famously given to Socrates to effect his execution (although somewhat alarmingly its dried hollow stems are often used by children as peashooters), chicory (Cichorium intybus), that colourful bright blue weed of Oxford roadsides whose roots have provided a coffee substitute, and henbane (Hyoscyamus niger), with its sinister appearance, and notoriously used by Dr Crippen to murder his wife, still occur in chalky areas: these are all ancient additions to our flora. You may wonder how the antiquity of plants is established.