What are the criteria for presuming native status

Decisions on native or alien status of British or Irish plants are based all too often on inappropriate criteria. on irrelevant emotions such as local patriotism, or misinterpretation of fossil data, or on an uncritical acceptance of earlier opinions. Neither abundance nor 'looking wild ' can be accepted as firm evidence of native status. The frequent practice of treating long-established aliens as equivalent to natives gives rise to confusion in discussions of phytogeography or quaternary history; the former may be hard to distinguish from natives. but they are aliens none the less. Eight criteria are here suggested; very seldom will any one of them give a definite answer. but if s.everal provide circumstantial evidence pointing in the same direction it is reason ~ to accept it as decisive. The criteria suggested are: fossil evidence; historical evidence; habitat; geographical distribution; ease of known naturalization elsewhere; genetic diversity; reproductive pattern; supposed means of introduction. A list is presented of species given without qualification as natives in the Flora of the British Isles (2nd ed.) by Clapham, Tutin and Warburg, whose status appears to the author to be subject to considerable doubt. The list is not exhaustive. THE PROBLEM Most Floras make some attempt to distinguish between native and introduced species, though som