The arctic-alpine polyploids Cerastium alpinum and C. nigrescens (Caryophyllaceae) in a sympatric situation: breakdown of species integrity?
2002
The high
polyploids
Cerastium alpinum(8x) and C. nigrescens (12x) were investigated in a mixed population in central Norway to evaluate whether hybridisation has resulted in continuous variation in morphology and genetic markers, a hypothesis previously proposed to account for the extensive taxonomic confusion in this
species group.
Isozyme, fertility, and morphological (37 characters) variation were examined among 347, 265, and 237 plants, respectively. A PCO analysis based on 23 quantitative morphological characters identified two main groups, corresponding to C. alpinum and C. nigrescens. The groups were also clearly separated in
isozymemarkers, several qualitative morphological characters, and chromosome numbers. Only 20 plants (8.4%) were more or less intermediate in the PCO analysis. These plants had a parental or hybrid
isozymemultilocus phenotype and typically few well-developed anthers, low pollen stainability, and no seed set. Several plants within the C. nigrescens group also had reduced pollen stainability. These results indicate that later-generation hybrids and/or
backcrossestowards C. nigrescens are formed. Thus, interspecific, interploidal gene flow probably occurs, but at rates that are insufficient to break down species integrity.
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