Hybridism in the Kunzea ericoides complex (Myrtaceae): an analysis of artificial crosses

Abstract

Observations of wild plants and herbarium specimens suggest that hybridism is a feature of the Australasian Kunzea ericoides (Myrtaceae) complex. In this study 73 artificial cross combinations were attempted with New Zealand material of Leptospermum scoparium, five Kunzea species, two varieties and six informally recognised entities within the New Zealand K. ericoides complex. The results of these crosses are documented, and for five hybrids spanning the intergeneric, interspecific and intraspecific crosses attempted, we provide a more detailed assessment based on morphology, molecular (nrDNA and chloroplast) sequence variation, and genomic in situ hybridisation (GISH). This is the first time GISH has been used in the Myrtaceae. Hybrids were easily generated between the New Zealand members of the K. ericoides complex, but not between them and the Australian K. ericoides complex. We were unable to produce hybrids between the New Zealand K. ericoides complex and two more distantly related Australian species, K. baxteri and K. parvifolia. Intergeneric crosses between New Zealand plants of Leptospermum scoparium, Kunzea sinclairii and an informally recognised variant K. aff. ericoides (b) were successfully produced, but failed to flower. The molecular evidence and observations after GISH show that even when low levels of sequence divergence exist, genome differentiation, to different extents, can be observed. The results confirm some suspected New Zealand hybrid complexes. However, while hybrids were easily generated artificially, natural instances of hybridism appear to be largely confined to those habitats significantly disturbed since European settlement of both countries.