ASPECTS OF ECOTYPIC DIFFERENTIATION IN THE PERENNIAL SOWTHISTLE

In The Netherlands, two ecotypes of the perennial sowthistle, Sonchus arvensis L., are found which differ markedly in leaf morphology. Only in exceptional cases do putative hybrids occur in areas close by sea. One ecotype is found only in coastal dunes, the other only in the interior. The latter ecotype is often identified as a troublesome weed.

An answer is given to the question as to what mechanisms are responsible for the difference in distribution pattern of the two ecotypes, based on results of germination physiology, growth physiology and the effect of mechanical disturbance.

The difference in distribution pattern is regulated as follows. The arable ecotype is prevented from occurring in the dune habitat by its poor germination ability under the temperature and moisture conditions of that environment. If germination does occur, the seedlings of the arable ecotype are unable to develop into adult individuals by the inability of forming an extensive root system to exploit dune sand poor in nutrients and moisture. The coastal ecotype is excluded from arable fields by its poor capacity to overcome mechanical disturbances.