Phylogenomics and the rise of the angiosperms

Angiosperms are the cornerstone of most terrestrial ecosystems and human livelihoods1,2. A robust understanding of angiosperm evolution is required to explain their rise to ecological dominance. So far, the angiosperm tree of life has been determined primarily by means of analyses of the plastid genome3,4. Many studies have drawn on this foundational work, such as classification and first insights into angiosperm diversification since their Mesozoic origins5-7. However, the limited and biased sampling of both taxa and genomes undermines confidence in the tree and its implications. Here, we build the tree of life for almost 8,000 (about 60%) angiosperm genera using a standardized set of 353 nuclear genes8. This 15-fold increase in genus-level sampling relative to comparable nuclear studies9 provides a critical test of earlier results and brings notable change to key groups, especially in rosids, while substantiating many previously predicted relationships. Scaling this tree to time using 200 fossils, we discovered that early angiosperm evolution was characterized by high gene tree conflict and explosive diversification, giving rise to more than 80% of extant angiosperm orders. Steady diversification ensued through the remaining Mesozoic Era until rates resurged in the Cenozoic Era, concurrent with decreasing global temperatures and tightly linked with gene tree conflict. Taken together, our extensive sampling combined with advanced phylogenomic methods shows the deep history and full complexity in the evolution of a megadiverse clade.

Composition and antimicrobial activity of the essential oils from the Phebalium squamulosum species complex (Rutaceae) in New South Wales, Australia

Essential oils have been hydrodistilled and characterized from 21 populations of taxa currently assigned to the endemic Australian species Phebalium squamulosum (Rutaceae: Boronieae) using GC-MS, NMR and quantified using GC-FID. Essential oils were further examined using principle component analysis to distinguish chemotypes, then screened for antimicrobial activity using broth dilution and TLC-bioautography. Collections of subspecies of P. squamulosum, namely subsp. coriaceum, subsp. gracile, subsp. lineare, subsp. squamulosum, subsp. ozothamnoides and subsp. verrucosum, were made from the wild and one from a cultivated plant of known provenance within New South Wales. Results demonstrated considerable intra- and interspecific essential oil component variation, suggesting the existence of distinct chemotypes and supporting previously observed segregate species based on morphological evidence. Antimicrobial testing revealed moderate to high activity for all essential oils dominated by sesquiterpene alcohols; elemol and eudesmol isomers. Conversely, very low antimicrobial activity was observed from essential oils dominated by monoterpenes. This study constitutes the most exhaustive investigation of essential oils from P. squamulosum subspecies to date and provides the first report of antimicrobial activity.

Dihydrotagetone, an Unusual Fruity Ketone, is Found in Enantiopure and Enantioenriched Forms in Additional Australian Native Taxa of Phebalium (Rutaceae: Boronieae)

Here we report for the first time hydrodistillation of leaf essential oils from Phebalium squamulosum subsp. verrucosum, P. glandulosum subsp. eglandulosum, P. glandulosum subsp. nitidum and P. glandulosum subsp. angustifolium (Rutaceae: Boronieae). Essential oils were analysed using gas-chromatography/mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR). With the exception of P. glandulosum subsp. angustifolium, all taxa yielded essential oils in relatively high amounts (1–3%, w/w) made up predominantly of 2,6-dimethyloct-7-en-4-one (dihydrotagetone). The essential oil from P. squamulosum subsp. verrucosum contains either (+)-dihydrotagetone ( ee 94–100%) or (-)-dihydrotagetone ( ee 17–18%). Taxonomically, these results support the proposal that P. squamulosum subsp. verrucosum may be specifically misplaced, phytochemically resembling the P. glandulosum complex. Similarly, P. glandulosum subsp. angustifolium phytochemically resembles P. distans or P. longifolium and also appears to be assigned incorrectly to the P. glandulosum group.

A new Australian species of Luffa (Cucurbitaceae) and typification of two Australian Cucumis names, all based on specimens collected by Ferdinand Mueller in 1856

As a result of his botanical explorations in northern Australia, Ferdinand von Mueller named several Cucurbitaceae that molecular data now show to be distinct, requiring their resurrection from unjustified synonymy. We here describe and illustrate Luffa saccata F. Muell. ex I.Telford, validating a manuscript name listed under Luffa graveolens Roxb. since 1859, and we lectotypify Cucumis picrocarpus F. Muell. and Cucumis jucundus F. Muell. The lectotype of the name Cucumis jucundus, a synonym of Cucumis melo, is mounted on the same sheet as the lectotype of Cucumis picrocarpus, which is the sister species of the cultivated Cucumis melo as shown in a recent publication.

Delimitation of Sauropus (Phyllanthaceae) based on plastid matK and nuclear ribosomal ITS DNA Sequence data

BACKGROUND AND AIMS

A recent molecular phylogenetic study showed that Sauropus is deeply embedded within Phyllanthus together with its allies, Breynia and Glochidion. As relationships within Sauropus are still problematic and the relationship with Breynia has long been doubted, more molecular data are needed to test/corroborate such a broad definition of Phyllanthus. This study aims to clarify the status and delimitation of Sauropus and establish its position within Phyllanthaceae.

METHODS

Plastid matK and nuclear ribosomal ITS DNA sequence data for Sauropus and its allies were used to construct phylogenetic trees using maximum parsimony and Bayesian methods.

KEY RESULTS

Within Phyllanthus, Sauropus can be split into the mainly south-east Asian Sauropus sensu stricto (s.s.) plus Breynia and the mainly Australian Sauropus (formerly Synostemon). Sauropus s.s. plus Breynia comprise two distinct clades; one is the combination of Sauropus sections Glochidioidei, Sauropus and Schizanthi and the other is the combination of Sauropus sections Cryptogynium and Hemisauropus and the monophyletic genus Breynia.

CONCLUSIONS

Molecular data indicate that Synostemon should be reinstated at the same level as Sauropus s.s. and that Sauropus s.s. should be united with Breynia under the latter, older name. The molecular data corroborate only two of the five infrageneric groups of Sauropus recognized on the basis of morphological data.