Morphological and AFLP-based Differentiation within the Taxonomical Complex Section Caninae (subgenus Rosa)

Abstract

The taxonomical structure of the polymorphic subgenus Rosa section Caninae is highly complex due to the combination of some unusual features: the unique polyploid chromosomal constitution, the heterogamic canina meiosis, the ability to hybridize interspecifically, and the predominantly matroclinal inheritance. Although most taxonomists agree on the subdivision of the section into three morphologically well-defined groups (Rubigineae, Vestitae, and Caninae), they disagree on the existence of smaller groups such as Tomentellae. The aim was to gain insight in the taxonomical structure and investigate the interpopulation differentiation of the polymorphic section Caninae by analysing morphological and AFLP-based characters of the seven most common Belgian dog-rose taxa. The intersubsectional and -specific relationships within the dog-roses were examined using morphological and molecular-genetic markers. AFLP data were analysed with basic descriptive genetic statistics because of the lack of Hardy-Weinberg equilibrium due to the polyploid genetic structure and heterogamic meiosis. Both the morphological and AFLP-based analyses supported the subdivision of the dog-roses in three well-defined though partly overlapping groups, Rubigineae, Vestitae and Caninae. However, it was not possible to distinguish between the morphologically well-defined taxa within the same subsection using AFLP-based data. In addition, the results suggested a high similarity of Rosa balsamica with subsection Caninae taxa. Small-scale geographical AFLP-based differentiation was observed within several dog-rose taxa. Surprisingly, individuals sampled at one locality and belonging to morphologically distinct dog-rose taxa displayed higher genetic similarities in comparison to their congeners sampled at different localities. The hybridogenic character of the dog-roses was reflected in the vague boundaries between the subsections and on the species level within the subsections. Indications were found for current or historical hybridization on the genetic structure of the population. No morphological or AFLP-based evidence was obtained to support the existence of the separate subsection Tomentellae.