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1. The evolutionary fate of natural hybridization is determined by the fitness of hybrids. Specifically, the survival of newly formed hybrids is affected by intrinsic genetic incompatibilities and/or genotype–environment interactions. The influence of these factors on the evolutionary potential of two natural hybrids of Narcissus has been assessed. Fitness components were estimated in early experimental F₁ hybrids as well as in natural hybrids of unknown descent.

2. To test the efficiency of reproductive isolation, fruit set, seed number and seed mass from interspecific crosses were measured, as were germination rate, radicle vigour and leaf appearance time in F₁ experimental hybrids in the greenhouse.

3. Germination rate, survival and the number of leaves produced were also measured in F₁ plants transplanted to eight natural sites and compared with plants growing under greenhouse conditions. In addition, to …