Disentangling the bindweeds: hybridization and taxonomic diversity in British Calystegia (Convolvulaceae)

作者：Brown Jacqueline M; Brummitt Richard K; Spencer Mark; Carine Mark A^*

来源：Botanical Journal of the Linnean Society, 2009, 160(4): 388-401.

DOI：10.1111/j.1095-8339.2009.00987.x

• Britain
• distribution
• evolution
• internal transcribed spacer region
• morphology
• sequence polymorphism

Calystegia is taxonomically complex. More than 65 taxa are currently recognized, but species circumscription is problematic, geographical intergradation between taxa is common and hybridization between species is known to occur. In this study, the nuclear ribosomal internal transcribed spacer 1 region (ITS1) was used to investigate the extent to which interspecific hybridization has contributed to the generation of taxonomic diversity in the C. sepium complex of the genus. Focusing principally on taxa that occur in Britain and their putative relatives, patterns of infra-individual ITS1 variation were examined by direct sequencing and cloning. Direct sequencing of the ITS region of 58 accessions representing 11 taxa and one hybrid revealed 22 variable positions that collectively defined 14 ribotypes. Diagnostic and invariant ribotypes lacking polymorphisms were found in C. sepium ssp. sepium, C. sepium ssp. limnophila, C. silvatica ssp. silvatica, C. pellita, C. pubescens and C. soldanella. Three ribotypes were recovered in C. sepium ssp. americana, two of which lacked polymorphisms, whereas the third exhibited two polymorphic sites. Calystegia sepium ssp. roseata, C. sepium ssp. spectabilis, C. silvatica ssp. disjuncta, C. pulchra and C. x howittiorum were each characterized by taxon-specific polymorphisms in the ITS1 region. In each case, the polymorphisms observed were consistent with the co-occurrence in the genome of nonpolymorphic ribotypes that were observed in other taxa. This observation is supported by cloning of the ITS region and is consistent with a hybrid origin for the taxa in which they occur. The hypotheses of hybridity proposed are further shown to be congruent with other data, notably morphology. This study suggests that taxonomic diversity within the C. sepium complex may have been promoted by hybridization. For at least some of the taxa investigated, it is at least possible that sympatry may have been achieved anthropogenically, through the introduction of taxa into cultivation. The processes revealed in this study may help to explain some of the taxonomic complexity observed in the genus more widely, although this remains to be tested.

• 出版日期2009-8