Systematics and biogeography of the Styphelieae (Epacridoideae, Ericaceae)

Puente Lelièvre, Caroline (2013) Systematics and biogeography of the Styphelieae (Epacridoideae, Ericaceae). PhD thesis, James Cook University.

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Considerable work has been undertaken over the last two decades toward a phylogenetic classification of the epacrids (Epacridoideae, Ericaceae). Generic level relationships have been resolved in all major clades, except for the Styphelia-Astroloma clade (tribe Styphelieae). With the aim of providing a foundation for a forthcoming generic revision of this clade, phylogenetic relationships and historical biogeographic patterns were investigated using parsimony, maximum likelihood, Bayesian inference and Bayesian relaxed-clock analyses of four chloroplast DNA markers (rbcL, matK, trnH-psbA, atpB-rbcL) and the nuclear-encoded ribosomal Internal Transcribed Spacer (ITS). With the aim of identifying new morphological synapomorphies to support the phylogenetic groups, a representative pollen survey within the Styphelieae, broadly sampling the Styphelia-Astroloma clade, was carried out to document the diversity of pollen types and morphology. These characters were optimised on the estimated molecular phylogeny to investigate their evolutionary patterns in the clade. Finally, to better understand the genetic variation at shallow phylogenetic branches and the possible factors driving diversification in the Styphelia-Astroloma clade, genetic structure in the Leucopogon conostephioides species complex was investigated using NeighborNet, Bayesian clustering, and Neighbor joining and parsimony phylogenetic analyses of Amplified Fragment Length Polymorphism (AFLP) data.

The monophyly of the Styphelia-Astroloma clade is strongly supported. Within this clade twelve well-supported lineages were resolved: Group I (Astroloma sensu stricto (s.s.), Group II and III (Styphelia sensu lato (s.l.)), Group IV (Leucopogon rotundifolius + L. cuneifolius), Group V (Leucopogon s.l. pro parte (p. p.)), Group VI (Styphelia s. s.), Group VII (Leucopogon s.l. p. p.), Group VIII (Leucopogon conostephioides complex), Group IX ('Stomarrhena'), Group X (Leucopogon s.l. p. p.), Group XI (Leucopogon blepharolepis + L. sp. Moore River), and Group XII (New Caledonian Styphelia s. l.). On the basis of these results, the genus Stenanthera is reinstated, and Astroloma baxteri A.. ex DC. and Leucopogon melaleucoides A.Cunn. ex DC. are transferred to the genera Brachyloma Sond. and Cunn Acrothamnus Quinn respectively.

The improved resolution of the phylogenetic relationships within Styphelieae provided the background for historical biogeographical studies. The origins and evolutionary relationships of the New Zealand Styphelieae were investigated because they epitomise the controversies on the biogeographic history of the New Zealand biota. Cyathodophyllum novaezelandieae (early Miocene, 20-23 million years (Ma)) constitutes evidence for the antiquity of the Styphelieae in New Zealand. Yet the extant species in the tribe are thought to be very closely related to or conspecific with Australian taxa, which suggests recent trans-Tasman origins. The results of parsimony, maximum likelihood and Bayesian phylogenetic analyses indicate that the sister taxa for each of the extant species of New Zealand Styphelieae is from Tasmania or the east coast of mainland Australia; except for Acrothamnus colensoi for which its sister is from New Guinea. Bayesian relaxed-clock analyses using direct and secondary fossil calibration methods suggest that all of the New Zealand lineages diverged from their non-New Zealand sisters within the last 7 Ma. Time discontinuity between C. novae-zelandiae and the origins of the extant New Zealand lineages indicates that the fossil and extant Styphelieae in New Zealand are not related. The relative dating analysis showed that to accept this relationship, it would be necessary to accept that the Styphelieae arose in the early-mid Mesozoic (210-120 Ma), which contradicts multiple lines of evidence on the age of angiosperms. Therefore, the results do not support the hypothesis that Styphelieae have been continuously present in New Zealand since the early Miocene. Instead they suggest a historical biogeographical scenario in which the lineage to which C. novaezelandiae belongs became extinct in New Zealand, and the extant New Zealand Styphelieae are derived from Australian lineages that recolonised (presumably by long distance dispersal) no earlier than the late Miocene to Pliocene.

Three different types of pollen were found in the representative pollen survey: 1) pseudomonads, present in all the species sampled within the Styphelia-Astroloma clade as well as in Monotoca, Oligarrhena and Leucopogon s.s.; 2) A-type (permanent tetras with variable sterility), observed in Acrothamnus, Acrotriche, Conostephium, Leptecophylla, Pentachondra involucrata, Stenanthera and Needhamiella pumilo; and 3) T-type (regular tetrads), present in Brachyloma, Lissanthe, and Pentacondra pumila. Pollen type records for the tribes Epacrideae, Cosmelieae, Prionoteae and Richeeae consist of regular tetrads. True regular monads were not recorded in Styphelieae.

Pseudomonads are universally distributed in the Styphelia-Astroloma clade.The taxonomic utility of pollen type in the clade is therefore limited. Conversely, pollen morphological characters such as exine ornamentation, number of pores and size of the mature tetrads show a variation that is consistent with the phylogenetic groups and seem promising to support a genus-level phylogenetic classification of the Styphelia-Astroloma clade. Moreover, these characters are potentially useful for a more accurate identification of pollen fossils in the Epacridoideae.

The phylogenetic analyses heightened further questions about the taxonomic significance of the morphological and the genetic diversity within the phylogenetic groups (I - XII). One of the groups that required additional examination was the Leucopogon conostephioides complex (group VIII).

Leucopogon conostephioides is a broadly circumscribed species with a wide distribution in Western Australia. The pattern of variation in the L. conostephioides complex is more consistent with the presence of several currently unrecognised, segregate taxa rather than with a single, highly variable species. NeighbourNet, Bayesian clustering and Neighbor joining and parsimony phylogenetic analyses of AFLP data from 52 individuals revealed four distinctive genetic groups that correspond to the four putative taxa sampled (Leucopogon conostephioides, L. sp. ‘short style’, L. sp. ‘Biffid Eneabba’ and L. sp. ‘Cockleshell Gully’). Hence, the genetic differentiation is congruent with the morphological variation observed in the species complex. While some individuals presented genetic admixture, the lack of morphological intermediates and of individuals appearing at the intersection of two splits on the NeighbourNet analysis suggest that this is due to retention of ancestral genetic elements rather than ongoing gene flow between populations. Potential reproductive barriers contributing to the genetic isolation are modifications in floral morphology, disparities in flowering times and edaphic isolation as a consequence of different soil type preferences. Both morphology and genetic structure within the L. conostephioides complex indicate that these groups are evolutionarily distinct and they should be recognised as different taxa.

Item ID: 57523
Item Type: Thesis (PhD)
Keywords: Styphelieae, Epacridoideae, Ericaceae, heaths, New Zealand flora
Copyright Information: Copyright © 2013 Caroline Puente Lelièvre
Date Deposited: 26 Mar 2019 02:08
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060310 Plant Systematics and Taxonomy @ 50%
06 BIOLOGICAL SCIENCES > 0604 Genetics > 060411 Population, Ecological and Evolutionary Genetics @ 25%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060302 Biogeography and Phylogeography @ 25%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 25%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960803 Documentation of Undescribed Flora and Fauna @ 50%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960899 Flora, Fauna and Biodiversity of Environments not elsewhere classified @ 25%
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