As old as the hills: Pliocene palaeogeographical processes influence patterns of genetic structure in the widespread, common shrub Banksia sessilis

The impact of Quaternary glaciation on the development of phylogeographic structure in plant species is well documented. In unglaciated landscapes, phylogeographic patterns tend to reflect processes relating to persistence and stochasticity, yet other factors, associated with the palaeogeographical history of the landscape, including geomorphological events, can also have a significant influence. The unglaciated landscape of south‐western Western Australia is an ideal location to observe these ancient drivers of lineage diversification, with tectonic activity associated with the Darling Fault in the late Pliocene attributed to patterns of deep phylogeographic divergence in a widespread tree from this region. Interestingly, other species within this region have not shown this pattern and this palaeogeographical boundary therefore presents an opportunity to examine age and historical distribution of plant species endemic to this region. In this study, we assess patterns of genetic diversity and structure across 28 populations of the widespread shrub Banksia sessilis using three cpDNA markers and nine nuclear microsatellite markers. Sixteen cpDNA haplotypes were identified, comprising two major chloroplast DNA lineages that are estimated to have diverged in the Pliocene, approximately 3.3 million years ago. This timing coincides with major geomorphological processes in the landscape, including the separation of the Darling Plateau from the adjacent Swan Coastal Plain, as well as eustatic changes on the Swan Coastal Plain that are likely to have resulted in the physical isolation of historical plant lineages. Chloroplast lineages were broadly aligned with populations associated with older lateritic soils of the Darling Plateau and Geraldton sandplains or the younger sandy soils associated with the Swan Coastal Plain and Southern Coastline. This structural pattern of lateritic versus non‐lateritic division was not observed in the nuclear microsatellite data that identified three genetic clades that roughly corresponded to populations in the North, South, and Central portions of the distributions

Lotononis angolensis forms nitrogen fixing, lupinoid nodules with phylogenetically unique, fast-growing, pink-pigmented bacteria, which do not nodulate L. bainesii or L. listii

Root-nodule bacteria that nodulate the legume genus Lotononis are being investigated to develop new forage species for agriculture. Bacteria isolated from nodules of Lotononis angolensis were fast-growing, highly mucoid and pink-pigmented, and on the basis of 16S rRNA phylogeny <94% related to other genera in the Alphaproteobacteria. Root-nodule bacteria isolated from other Lotononis species (L. bainesii, L. solitudinis and L. listii) resembled the more common dry, slow-growing, pink-pigmented rhizobia previously described for L. bainesii. These isolates could be attributed to the Methylobacterium genus, although not to the type species Methylobacterium nodulans. Further differences were uncovered with nodulation studies revealing that nodule isolates from L. angolensis were effective at nitrogen fixation on their host plant, but could nodulate neither L. bainesii nor L. listii. Reciprocal tests showed isolates from L. bainesii, L. listii and L. solitudinis were incapable of nodulating L. angolensis effectively. Nodule morphology for L. bainesii, L. angolensis and L. listii was characteristically lupinoid, with little structural divergence between the species, and with nodules eventually enclosing the entire root