Phylogenetic relations in tribe Leucocoryneae (Amaryllidaceae, Allioideae) and the validation of Zoellnerallium based on DNA sequences and cytomolecular data

Abstract

Tribe Leucocoryneae comprises the genera Beauverdia, Ipheion, Leucocoryne, Nothoscordum, Tristagma and Zoellnerallium, a more recently described genus, the validity and relationships with the other genera of the tribe of which are still unclear. The present work aims to characterize the karyotype of Zoellnerallium and to evaluate the phylogenetic relationships among the genera of Leucocoryneae. The phylogeny of the tribe was reconstructed based on trnG intron plastid and internal transcribed spacer nr(ITS) nuclear sequences. Karyotype description of the two Zoellnerallium spp. was based on chromosome morphometry, DAPI and CMA fluorochrome staining, rDNA sites and silver nitrate staining. Phylogenetic analyses indicated that all genera of Leucocoryneae, except Beauverdia (included in Nothoscordum), are monophyletic. Nothoscordum spp. appeared as sister to a major clade of Leucocoryneae (Ipheion + Tristagma and Leucocoryne + Zoellnerallium). The two Zoellnerallium spp. had 2n = 24 (8M + 16A). The occurrence of two pairs of 5S rDNA sites in Zoellnerallium and tetraploids of Nothoscordum spp. further supports the tetraploid nature of this genus. The higher diploid number of Zoellnerallium was due to centric fissions followed by the emergence of a 45S rDNA cluster on the short arm of the new acrocentric chromosomes. The data suggest that Zoellnerallium spp. are tetraploids with a basic number x = 12 (4M + 8A), whereas the ancestor diploid karyotype with n = 3M + 2A is currently present only in Nothoscordum and Leucocoryne. Different combinations of karyotypic changes may have led to the isolation of lineages and formation of most genera in Leucocoryneae.