Clone Structure in Four Solidago altissima (Asteraceae) Populations: Rhizome Connections within Genotypes

We studied clone structure and degree of genotypic mixing of Solidago altissima L. (Asteraceae) clones in four old fields near Ithaca, New York. The fields differed in time from agricultural abandonment and were approximately 1, 5, 20, and 35 years old. In the three older fields, three 0.75 m2 plots were excavated intact and rhizome connections among ramets were mapped. In the youngest field 30 ramets were dug up singly. The genotype of all ramets was determined using electrophoresis of four polymorphic enzyme systems. Fields differed in the number and dispersion of genotypes within plots, and the degree of connection among ramets in the same clone. The one-year-old field was composed of single ramet genotypes which had probably established from seed the previous year. The five-year-old field contained many small contiguous clones of S. altissima with highly interconnected ramets. In the oldest two fields clones were highly intermixed and ramets of the same genotype were not extensively interconnected. These results demonstrate that clones of S. altissima display considerable phenotypic variability between fields and patterns of clone development may differ. The causes of this variability remain to be identified. We suggest that either selection for different genotypes or changing habitat conditions during succession may lead to changes in clone form.