Phylogeny of Acronychia (Rutaceae) and First Insights into Its Historical Biogeography and the Evolution of Fruit Characters

Abstract

BackgroundThe genus Acronychia (Citrus family, Rutaceae) contains 49 species of trees and shrubs that are found mainly in rain forest. The genus has a large distributional range from mainland southern Asia to Australia and New Caledonia, but most species are endemic to either New Guinea or Australia. This study aimed to provide the first detailed molecular phylogeny of Acronychia and use it to test the taxonomic value of fruit morphological characters, and infer the historical biogeography of the genus.MethodologyPhylogenetic analyses (Bayesian Inference, Maximum Likelihood) were undertaken on nucleotide sequence data from two plastid (psbA-trnH, trnL-trnF) and three nuclear markers (ETS, ITS, NIAi3) from 29 Acronychia species (59% of the genus) and representatives of related genera.Results and ConclusionsThe results indicate that the South-East Asian genus Maclurodendron is nested phylogenetically within Acronychia and must be synonymized to render Acronychia monophyletic. Fruit morphological characters have been used previously to infer relationships within Acronychia and our analyses show that these characters are informative for some subclades but are homoplasious for the group as a whole. Apocarpous fruits are the ancestral state in Acronychia and subapocarpous and fully syncarpous fruits are derived. The unisexual flowers of Maclurodendron are derived from bisexual flowers, which are found in all species of Acronychia as well as its relatives. Acronychia probably first evolved on Australia with range expansion to New Guinea via stepping-stone dispersal or direct land connections within the Sahul Shelf, followed by two independent dispersals to areas west of New Guinea. Most species of Acronychia occur in either Australia or New Guinea, but no species occurs in both regions. This is surprising given the close proximity of the landmasses, but might be explained by ecological factors.

Historical biogeography of Melicope (Rutaceae) and its close relatives with a special emphasis on Pacific dispersals

“…The phylogenetic reconstructions are congruent with Appelhans et al (, ) and Holzmeyer et al () and are not described or discussed in detail here. The Acronychia ‐ Melicope clade shows the same four main clades as described by Appelhans et al (), and also the sister relationships of Acronychia ‐ Melicope with Medicosma , and of Acronychia ‐ Melicope ‐ Medicosma with Tetractomia are supported (Figs.…”

“…The taxon sampling of this study was largely based on that of Appelhans et al (, ) and Holzmeyer et al () with several additional species mainly from Pacific archipelagos sampled. A total number of 332 specimens, representing 164 species and 16 genera, were included in this study (Table ): Melicope (118 out of 235 species and 12 unidentified specimens), Acronychia (24/48), Brombya (1/2), Comptonella (4/8), Dutaillyea (1/2), Euodia (4/6), Maclurodendron (1/6), Medicosma (1/25), Perryodendron (1/1), Picrella (2/3), Pitaviaster (1/1), Sarcomelicope (1/9), Tetractomia (1/6).…”

“…& G.Forst. to ensure monophyly of each genus (Appelhans et al, , ; Holzmeyer et al, ). Melicope (∼240 spp.)…”

“…Acronychia (49 spp.) is the second largest genus of the Acronychia ‐ Euodia ‐ Melicope group and is mainly confined to eastern Australia and New Guinea with two species extending west to Java and India, and two eastward to the Solomon Islands and New Caledonia (Hartley, , ; Holzmeyer et al, ). Euodia (7 spp.)…”

Evolution of Melicope J.R.Forst & G.Forst (Rutaceae), the largest adaptive radiation of woody plants on the Hawaiian Islands.

“…The data sets contained up to seven nuclear and chloroplast coding and non-coding marker regions from up to 164 species from 26 genera and covering the entire geographic range of the group. The results show that the genera in the Acronychia-Euodia-Melicope group are not monophyletic in their current circumscription (Appelhans et al, 2014a(Appelhans et al, , 2014bHolzmeyer et al, 2015). The group is broadly divided into two main clades; the species-poor Euodia clade and the species-rich Acronychia-Melicope clade, which contains all but one described Melicope species included in the data sets.…”