Peter G. Wilson

Clades, Clocks, and Continents: Historical and Biogeographical Analysis of Myrtaceae, Vochysiaceae, and Relatives in the Southern Hemisphere

Some of the most interesting but still most contentious disjunct biogeographical distributions involve Southern Hemisphere tropical and warm temperate families. The PHMV clade of Myrtales includes four families (Psiloxylaceae, Heteropyxidaceae, Myrtaceae, and Vochysiaceae) that exhibit a number of these biogeographical patterns. The related Psiloxylaceae and Heteropyxidaceae are small families restricted in distribution to the recent volcanic Mascarene Islands to the east of Madagascar and to southeast Africa, respectively. Myrtaceae are found on three major Gondwanan regions (South America, Australasia, and Africa). Because the New World taxa are almost exclusively fleshy fruited, it is unclear whether the family distribution is a classic Gondwanan vicariance pattern or results from one or more long‐distance dispersal events over ocean barriers. The Vochysiaceae represent one of a handful of families with amphi‐Atlantic distributions vigorously argued to support both long‐distance dispersal over the Atlantic and vicariance of western Gondwanan biota by Atlantic seafloor spreading. Molecular phylogenetic relationships, fossil dating of nodes, and penalized likelihood rate smoothing of maximum likelihood trees were employed for a Myrtales‐wide analysis using rbcL and ndhF and an analysis of the PHMV analysis using ndhF and matK. The results indicate that the PHMV differentiated during the late Cretaceous. The African lineage of Vochysiaceae is nested within a South American clade and probably arose via long‐distance dispersal in the Oligocene at a time when the Atlantic had already rifted 80 m.yr. at the equatorial region. The African/Mascarene Island families, most closely related to Myrtaceae, differentiated during the late Eocene, with subsequent but recent long‐distance dispersal from Africa to the Mascarenes. Myrtaceae show a rapid differentiation of a basal, paraphyletic subf. Leptospermoideae in Australasia. Fleshy‐fruited taxa (subf. Myrtoideae) are not monophyletic. Vicariance of a widespread warm temperate Southern Hemisphere distribution is likely in explaining the South American–Australasian disjunction, with subsequent dispersal events between the two and to Africa and the Mediterranean basin.

Myrtaceae revisited: a reassessment of infrafamilial groups

Cladistic analyses are presented of matK sequence data as well as a nonmolecular database for an identical set of exemplar species chosen to represent the core genera or groups of genera in Myrtaceae. Eleven robust clades are recognized on the molecular data. Polyphyly of the previously recognized Metrosideros and Leptospermum alliances is confirmed, and several smaller informal taxonomic groupings are recognized from among the members of the former alliance, i.e., the Tristania, Tristaniopsis, Metrosideros, and Lophostemon groups. The nonmolecular analysis provides only limited resolution of relationships. A degree of congruence exists between the two analyses in that two separate fleshy-fruited clades, the Acmena and Myrtoid groups, are identified, as are the Eucalypt and Tristania groups, and Psiloxylon and Heteropyxis are the first lineages to diverge in both analyses. A combined analysis recognized all 11 clades that received strong support from the molecular data. A high level of homoplasy is revealed in many of the nonmolecular characters when they are examined against the combined estimate of phylogeny.

Interfamilial Relationships in Myrtales: Molecular Phylogeny and Patterns of Morphological Evolution

Numerous phenotypic (morphological, palynological, cytological, and anatomical) studies have been conducted on Myrtales, yet the detailed relationships among the families of the order remain elusive. In this paper, the rbcL sequences of 50 taxa (39 representatives of Myrtales and 11 rosid outgroups) were analyzed using parsimony and maximum likelihood to provide a phylogenetic hypothesis of intraordi- nal relationships in Myrtales. The congruence between the phenotypic data from an earlier study and the rbcL topology was assessed to identify the potential synapomorphies that would corroborate the clades supported by the molecular tree. The rbcL consensus tree defined two major clades in the order. The first clade comprised a Myrtaceae lineage sister to a Melastomataceae lineage and the second clade included Onagraceae, a Lythraceae lineage, and Combretaceae. Phenotypic characters suggest that the ancestor of the first clade was characterized by the acquisition of fibrous seed exotegmen, while the ancestor of the second clade had flowers with stamens inserted directly on the rim of the hypanthium. However, branch support for the basal split of Myrtales is weak, possibly as a result of rapid early radiation in the order.

Investigating the host-range of the rust fungus Puccinia psidii sensu lato across tribes of the family Myrtaceae present in Australia.

The exotic rust fungus Puccinia psidii sensu lato was first detected in Australia in April 2010. This study aimed to determine the host-range potential of this accession of the rust by testing its pathogenicity on plants of 122 taxa, representative of the 15 tribes of the subfamily Myrtoideae in the family Myrtaceae. Each taxon was tested in two separate trials (unless indicated otherwise) that comprised up to five replicates per taxon and six replicates of a positive control (Syzygium jambos). No visible symptoms were observed on the following four taxa in either trial: Eucalyptus grandis×camaldulensis, E. moluccana, Lophostemon confertus and Sannantha angusta. Only small chlorotic or necrotic flecks without any uredinia (rust fruiting bodies) were observed on inoculated leaves of seven other taxa (Acca sellowiana, Corymbia calophylla ‘Rosea’, Lophostemon suaveolens, Psidium cattleyanum, P. guajava ‘Hawaiian’ and ‘Indian’, Syzygium unipunctatum). Fully-developed uredinia were observed on all replicates across both trials of 28 taxa from 8 tribes belonging to the following 17 genera: Agonis, Austromyrtus, Beaufortia, Callistemon, Calothamnus, Chamelaucium, Darwinia, Eucalyptus, Gossia, Kunzea, Leptospermum, Melaleuca, Metrosideros, Syzygium, Thryptomene, Tristania, Verticordia. In contrast, the remaining 83 taxa inoculated, including the majority of Corymbia and Eucalyptus species, developed a broad range of symptoms, often across the full spectrum, from fully-developed uredinia to no visible symptoms. These results were encouraging as they indicate that some levels of genetic resistance to the rust possibly exist in these taxa. Overall, our results indicated no apparent association between the presence or absence of disease symptoms and the phylogenetic relatedness of taxa. It is most likely that the majority of the thousands of Myrtaceae species found in Australia have the potential to become infected to some degree by the rust, although this wide host range may not be fully realized in the field.

Molecular systematics of the Leptospermum suballiance (Myrtaceae)

Two chloroplast regions, the matK gene and the atpb –rbcL intergenic spacer, were sequenced for 31 species of the Leptospermum suballiance. Both regions proved to be highly informative of relationships within the suballiance. Cladistic analyses confirm the monophyly of the Leptospermum suballiance but not of the Leptospermum alliance. Neither Agonis nor Leptospermum is monophyletic and there is no support for the distinctness of Angasomyrtus from Kunzea. The utility of the rps16 intron for this group was also investigated but further work on this region was discontinued because of primer incompatibility.

Morphological and Molecular Evidence of Polyphyly in Rhodomyrtus (Myrtaceae: Myrteae)

Abstract The monophyly of the genus Rhodomyrtus (Myrtaceae) was tested using data from morphology and the nuclear ribosomal ITS regions (ITS-1, ITS-2) and 5.8S gene. Representative species from baccate genera hypothesized to be closely related to Rhodomyrtus were included, such as Archirhodomyrtus, Octamyrtus, Knnakomyrtus, and some genera believed to be more distantly related, including Rhodamnia, Decaspermum, Pilidiostigma, and Myrtastrum. Up to four capsular-fruited outgroup species were used to root the trees (Heteropyxis natalensis, Carpolepis tardiflora, Lophostemon confertus, and Metrosideros rotundifolia). Morphological data using neighbor joining scattered species of Rhodomyrtus across several branches but generally recovered genera other than Rhodomyrtus. Using parsimony, the morphological data analysis also rejected the monophyly of Rhodomyrtus and resulted in consensus trees with relatively low resolution and bootstrap support. Based on traditionally recognized generic boundaries, results from DNA sequence data (parsimony, Bayesian analysis) rejected the hypothesized monophyly of Rhodomyrtus and typically dispersed species of Rhodomyrtus irregularly into two relatively large branches designated as Clades A and B. Species other than Rhodomyrtus contained in either Clade A or B from the molecular results were some, but not all, members of Archirhodomyrtus, Octamyrtus, and Knnakomyrtus. Partition tests indicated that phylogenies based on morphological characters differed significantly from those based on molecular data so a combined analysis was not conducted. DNA sequence variation ranged from no variation among sequences within a species up to 61 base pair differences plus four 1 or 2 bp gaps between Rhodomyrtus misimana and R. mcmtana. Although results from morphological and molecular analyses reject the hypothesis that Rhodomyrtus is monophyletic, additional data are needed before Rhodomyrtus can be split confidently into demonstrably monophyletic genera.

Pollen morphology of the Myrtaceae. Part 3: Tribes Chamelaucieae, Leptospermeae and Lindsayomyrteae

The pollen morphology of 36 genera and 147 species from the Myrtaceae tribes Chamelaucieae, Leptospermeae and Lindsayomyrteae was surveyed using scanning electron microscopy (SEM) and light microscopy (LM). Syncolpate pollen were observed in all genera of Leptospermeae and some genera of Chamelaucieae. Genera of tribe Chamelaucieae displayed five distinct colpal morphologies, which makes it the tribe with the most diverse pollen in Myrtaceae. Six genera of Chamelaucieae, including Actinodium, Chamelaucium, Darwinia, Homoranthus, Pileanthus and Verticordia, produce large acolpate pollen not observed in any other Myrtaceae. Two of these genera produce distinct pollen; Actinodium is the only genus to have prolate-spheroidal shaped pollen, and Pileanthus pollen is large and dicolporate. A number of anomalous aperture types occurred in species of Chamelaucieae, including monocolporate (Homoranthus thomasii), pentacolporate (Calytrix oldfieldii) and hexacolporate (Sannantha tozerensis). Pollen of Lindsayomyrteae appeared similar to those of Leptospermeae and Chamelaucieae, and on the basis of pollen features, could be related to these two tribes.

Anetholea (Myrtaceae), a new genus for Backhousia anisata: a cryptic member of the Acmena alliance

The taxonomic position of Backhousia anisata is reassessed on morphological and anatomical grounds and its affinities found to lie with the Acmena alliance. Backhousia anisata is glabrous and has a suite of wood anatomical character-states that are more consistent with a phylogenetic position in or near the Acmena alliance than with other Backhousia species; molecular data also support this placement. Since this species lacks the fleshy fruit, thick cotyledons and hypogeal germination characteristic of other members of the Acmena alliance, a new genus Anetholea Peter G.Wilson is described to accommodate it, and the new combination Anetholea anisata (Vickery) Peter G.Wilson made.

Re-evaluation of the genus Babingtonia (Myrtaceae) in eastern Australia and New Caledonia

The validity of the generic concept of Babingtonia Lindl. adopted by Bean (1997a) is tested in the light of molecular and morphological data. Molecular analyses support recognition of segregate genera, none of which is closely related to the type of the genus, Babingtonia camphorosmae, a western Australian species. Two genera, Sannantha and Kardomia, are described as new and a third genus, Harmogia, resurrected from synonymy; new combinations are provided in the new genera. A fourth group, consisting of ‘Babingtonia’ behrii and its allies, appears distinct but, as a predominantly southern group, with numerous western Australian representatives, is not treated further.

Phylogenomics of the green ash eucalypts (Myrtaceae): a tale of reticulate evolution and misidentification

Abstract. Eucalyptus is a genus that occurs in a range of habitats in Australia, Papua New Guinea, Timor, Sulawesi and the Philippines, with several species being used as sources of timber and fibre. However, despite its ecological and commercial significance, understanding its evolutionary history remains a challenge. The focus of the present study is the green ashes (subgenus Eucalyptus section Eucalyptus). Although previous studies, based primarily on morphology, suggest that the green ashes form a monophyletic group, there has been disagreement concerning the divergence of taxa. The present study aims to estimate the phylogeny of the green ashes and closely related eucalypts (37 taxa from over 50 locations in south-eastern Australia), using genome-wide analyses based on Diversity Arrays Technology (DArT). Results of analyses were similar in topology and consistent with previous phylogenies based on sequence data. Many of the relationships supported those proposed by earlier workers. However, other relationships, particularly of taxa within the Sydney region and Blue Mountains, were not consistent with previous classifications. These findings raise important questions concerning how we define species and discern relationships in Eucalyptus and may have implications for other plant species, particularly those with a complex evolutionary history where hybridisation and recombination have occurred.