Chromosomal evolution in Araliaceae and close relatives

Abstract

Chromosome numbers of 45 accessions representing 16 genera and 37 species of Araliaceae are herein reported, of which 30 species and seven genera (Apiopetalum, Arthrophyllum, Delarbrea, Merrilliopanax, Metapanax, Myodocarpus, and Pseudosciadium) are recorded for the first time. The evolution of this character is also examined in light of recent hypotheses of phylogenetic relationships. Chromosome numbers in the family are relatively uniform, generally with 2n = 24 or 48. However, the genus Hedera exhibits extreme variability, with a polyploid series ranging from 2n = 48 to 192. The basic number of Araliaceae is inferred to be x = 12, although x = 6 cannot be ruled out. The “Asian palmate” clade, the largest of the three major clades of core Araliaceae, is primarily characterized by polyploidy, although several genera have sometimes been regarded as evolutionarily “primitive”. By contrast, Aralia, Panax, and Polyscias (representing other major clades within the family) include species with both diploids and tetraploids. Four genera recently segregated from core Araliaceae (Apiopetalum, Delarbrea, Myodocarpus, and Pseudosciadium) are reported as n = 12. The formerly apiaceous Hydrocotyle (now placed in Araliaceae) is best interpreted as x = 12, although some aneuploid species may exist with x = 9. Hydrocotyle also exhibits extensive variation in ploidal level. Within Araliaceae, chromosomal variation is largely related to ploidal level, with relatively few cases of aneuploidy, such as those documented in Panax ginseng and Hydrocotyle. The available data are largely consistent with the hypothesis that the basic chromosome number of Apiales is x = 6.

Major repeat components covering one‐third of the ginseng (Panax ginseng C.A. Meyer) genome and evidence for allotetraploidy

“…The allotetraploid nature and genome evolution of ginseng Ginseng and American ginseng both experienced two rounds of genome duplication , and previous studies have suggested that the Panax species with 2n = 48 are likely to be allopolyploids because analyses from chloroplast intergenic regions versus internal transcribed spacer (ITS) datasets exhibited incongruent phylogenies (Lee and Wen, 2004;Yi et al, 2004). In this study, we found two unique FISH signal pairs from the genic probes (Figures 3f and S1c).…”

“…Ginseng has 2n = 48 chromosomes (Waminal et al, 2012) and has been regarded as tetraploid (2n = 4x), based on chromosome numbers of 2n = 24 and 48 among species in the genus Panax and generally in the family Araliaceae (Wen, 1999;Yi et al, 2004). The size of the ginseng genome is estimated to be 3.12 Gbp per haploid chromosome equivalent (Hong et al, 2004), whereas American ginseng, which recently diverged from ginseng , has an estimated genome size of 4.91 Gbp (Obae and West, 2012).…”

Phylogeny and Biogeography of Ivies (Hedera spp., Araliaceae), a Polyploid Complex of Woody Vines

“…Origins of Polyploidy-Polyploidy is widespread within Hederá, unlike most members of the Araliaceae, but the incidence of auto-and allopolyploidy is poorly understood (Yi et al 2004). McAllister and Rutherford (1990) inferred an allopolyploid origin of H. hibernica from diploid H. helix and H. maroccana on the basis of leaf morphology, trichome structure, and foliage odor.…”

First report of chromosome numbers of the Carlemanniaceae (Lamiales)

“…Chromosome base numbers reflect evolutionary relationships within families, as well as within orders (e.g., Apiales: Yi et al 2004;Laurales: Oginuma and Tobe 2006;Crossosomatales: Oginuma et al 2006). Our results contribute not only to providing missing data for the Carlemanniaceae, but also to a better understanding of its evolutionary relationships.…”