Plant hybrids in the wild: evidence from biological recording

Although plant hybrids are under‐recorded by botanists, the hybrids of Britain and Ireland are as well known as those of any comparable area. Of the 909 accepted hybrids, 301 have at least one alien parent and these include 152 taxa that have been introduced to the wild (usually from horticultural sources) as hybrids. The parental distributions of the spontaneous hybrids are described as either nested or overlapping; some of the most remarkable hybrids have parents with contrasting European distributions that overlap very narrowly. There are few annual or biennial hybrids and they tend to be sterile and closely associated with the parents, except for numerous annual Euphrasia hybrids. Perennial hybrids with moderate fertility or the capacity for vegetative reproduction are recorded on average from more hectads than sterile, non‐clonal perennials and some show considerable independence of their parental distributions. This independence may result from the decline of one parent or the spread of the hybrid; in many cases the explanation is unknown. Molecular methods have made invaluable contributions to our knowledge of some hybrids in recent years, but universal identification tools cannot currently be applied to plant hybrids so progress with such studies is likely to be piecemeal and slow.