Biology subjects

Christenhusz, M. J. M.

Publications and source records attributed to Christenhusz, M. J. M..

3 recordsLinked to original sources

bioRxiv2025

Puzzling parasitic plants: phylogenetics and classification of Santalales revisited

Based on a previously published but realigned matrix for Santalales, we find many relationships that were weakly or unsupported in previous studies are here much better supported, providing a more robust foundation upon which to discuss Santalales classification. In the maximum likelihood analysis, we recovered the same basic relationships as in the previous studies, but with two major differences: i) Balanophoraceae in the broad sense are monophyletic and well supported as embedded in Santalaceae (rather than biphyletic and outside Santalaceae) and ii) most of the former Olacaceae form a moderately supported clade (rather than a weakly supported grade). In the parsimony analysis, the position of Balanophoraceae s.l. is not well supported (although their broader circumscription is). We outline three possible options for a classification of the order and propose a new familial and subfamilial classification for Santalales. This hopefully provides a stable, user- friendly taxonomic framework that is phylogenetically well supported and more consistent with historical usage than some recently proposed systems, and provides taxa that can be more readily diagnosed morphologically. We recommend recognition of nine families (in phylogenetic sequence): Strombosiaceae, Erythropalaceae, Olacaceae, Opiliaceae, Santalaceae, Misodendraceae, Schoepfiaceae and Loranthaceae, plus an unresolved position for Balanophoraceae (including Mystropetalaceae), which we propose to exclude from Santalaceae until more evidence of their relationships to that family is available from nuclear genes. Four new subfamilies, Gaiadendroideae, Comandroideae, Nanodeoideae and Thesioideae, are proposed, and a new combination, Loranthus obtusifolius, is made.

evolutionary biology↗

bioRxiv2024

Recent speciation and adaptation to aridity in the ecologically diverse Pilbara region of Australia enabled the native tobaccos (Nicotiana; Solanaceae) to colonize all Australian deserts

For the last six million years, the arid Australian Eremaean Zone (EZ) has been as dry as today. An accepted hypothesis, applied to arid regions worldwide, suggests that flora and fauna were more broadly distributed before aridification began. In Australia, this aridification process started around 20 million years ago (Mya), leading to gradual speciation processes via vicariance as the climate became increasingly arid. Here, we use genomic data to investigate the biogeography and timing of divergence of native allotetraploid tobaccos, Nicotiana section Suaveolentes (Solanaceae), which putatively entered the EZ 5 Mya. The original allotetraploid migrants from South America were adapted to mesic areas of Australia and putatively radiated recently in the EZ, including sandy dune fields (only 1.2 My old), after developing drought adaptations. Based on coalescent and maximum likelihood analyses designed to corroborate timing of the Australian radiation independently, arrival of Nicotiana section Suaveolentes on the continent occurred approximately 6 Mya, and ancestors of the Pilbara (Western Australian) lineages radiated there at the onset of extreme aridity 5 Mya by locally adapting to these various ancient, highly stable habitats. The Pilbara thus served as both a mesic refugium and cradle for adaptations to harsher conditions. This dual role is due to its high topographical diversity, providing microhabitats with varying moisture levels, and its proximity to the ocean, which buffers against extreme aridity. Consequently, species like Nicotiana have been able to survive in mesic refugia during arid periods and subsequently adapt to more arid conditions. These results demonstrate that initially poorly adapted plant groups can develop novel adaptations in situ, permitting extensive and rapid wide dispersal despite the highly variable and unpredictable extremes of heat and drought in the EZ.

evolutionary biology↗

bioRxiv2022

Variation of the Rdr1 gene insertion in wild populations of Nicotiana benthamiana (Solanaceae) and insights into recent species divergence

O_LIOne of the most commonly encountered and frequently cited laboratory organisms worldwide is classified taxonomically as Nicotiana benthamiana (Solanaceae), an accession of which, typically referred to as LAB, is renowned for its unique susceptibility to a wide range of plant viruses and hence capacity to be transformed using a variety of methods. However, the origin and age of LAB and the evolution of N. benthamiana across its wide distribution in Australia remains relatively underexplored. C_LIO_LIHere, we have used multispecies coalescent methods on genome-wide single nuclear polymorphisms (SNPs) to assess species limits, phylogenetic relationships and divergence times within N. benthamiana. C_LIO_LIOur results show that the previous taxonomic concept of this species in fact comprises five geographically, morphologically and genetically distinct species, one of which includes LAB. C_LIO_LIRemarkably, we provide clear evidence that LAB is closely related to accessions collected further north in the Northern Territory; this species split much earlier from their common ancestor than the other four in this clade and is morphologically the most distinctive. Furthermore, this long-isolated species typically grows in sheltered sites in subtropical/tropical monsoon areas of northern Australia, contradicting the previously advanced hypothesis that this species is an extremophile that has traded viral resistance for precocious development. C_LI

evolutionary biology↗