Conference presentation: Biogeographic history and evolution of the two Australian mesic temperate floras

I presented my PhD proposal at the recent Australasian systematics conference – jointly held by the Australasian Systematic Botany Society and Society of Australian Systematic Biologists in Adelaide (November 2017).

Abstract:

Understanding how and why disparities in diversity across regions and taxonomic groups arise is one of the primary goals of biology. Current interest focuses on comparative studies on hotspot regions and their counterparts across the globe, with debates on whether differences in clade age or diversification rates are the primary drivers in the differences in taxonomic richness across regions. Here, I’ll focus on the two Australian temperate floras, distinguished by the southwest hotspot region for species richness and non-hotspot region in the southeast. Many floristic elements across both regions arose prior to their separation, where lineages were widespread across the Australian continent and subsequently retreated to the southern mesic fringes due to progressive aridification of the continent since the Miocene. Available paleorecords and phylogenies across the two regions support the clade-age hypothesis, where evidence indicate an earlier differentiation of current dominant flora elements in the southwest than compared with the southeast. However, studies on differences in diversification rates across the regions are currently lacking and so far have not been explicitly tested. I will first review theories that serve to explain these differences in richness, then current studies on this topic, and finally propose an evolutionary framework to guide further research on this area.

New Calytrix species in southwestern Australia

Following our work on the Calytrix acutifolia complex (Myrtaceae), four species are recognised, one of which is described as new to science. The results are published in the current issue of the Nuytsia journal: link to the article here.

Prior to our revision, the complex consists of one described taxon (Calytrix acutifolia, and four informal, phrase-named taxa (for more information on the Australian plant phrase-naming system see these links: A, B):

  •  Calytrix sp. Eneabba (B.J. Lepschi & T.R. Lally BJL3617)
  • Calytrix sp. Esperance (M.A. Burgman 4268A)
  • Calytrix sp. Tutunup (G.J. Keighery & N. Gibson 2953)
  • Calytrix sp. Wheatbelt (R. Davis 4544)

Based on a detailed study of morphological variations from herbarium specimens across these taxa:

  •  C. sp. Tutunup is described as new – C. retrorsifolia Nge & Keighery
  •  C. sp. Esperance (with holotype Lhotskya hirta) is recombined into Calytrix as C. hirta (Regel) Nge & K.R.Thiele
  • C. sp. Eneabba and C. sp. Wheatbelt are recombined as C. cravenii Nge & K.R.Thiele
  • C. acutifolia s. str. is recircumscribed as the fourth member of the complex
Morphology and habitat of study species. A – Calytrix cravenii Calingiri form (K.R. Thiele 4006); B – C. hirta (K.R. Thiele 5408); C – habitat of C. hirta; D – resprouting shrub of C. hirta (K.R. Thiele 5408). Photographs by K. Thiele (A, B) and F. Nge (C, D).

 

Distribution of Calytrix acutifolia (open circle), C. hirta (open square), C. retrorsifolia (star), and C. cravenii (closed circle) in south-west Western Australia.

 

Calytrix retrorsifolia. Photo: Francis Nge
Calytrix retrorsifolia. Photo: Francis Nge

New Hibbertia species in southwestern Australia

A new rare Hibbertia species (Hibbertia sejuncta K.R. Thiele & Nge; Dilleniaceae) just got described and published in the most recent issue of the Nuytsia journal, following our work on this group. Link to the article here

This new species differs from all other Western Australian Hibbertia by its combination of:

  •  stamens arranged all around the three glabrous carpels,
  • with two free stamens and three bundles of three stamens each,
  • linear, pilose leaves with the lamina very narrow but distinctly recurved either side of a prominent midrib.
Hibbertia sejuncta. Photo: Francis Nge

It is restricted in range, being confined to just several localities near Tenterden and Lake Muir, and hence is currently classified as a Priority Two species of conservation significance under the Department of Wildlife Conservation Codes for Western Australia Flora (under Hibbertia sp. Tenterden (M. Sowry 154) ).

This new species belongs in Hibbertia Andrew subgen. Hibbertia (Wheeler 2002), with close allies (based on morphological characters examined) to include:

  • H. helianthemoides (Turcz.) F.Muell
  • H. depressa (Steud.)
  • H. fitzgeraldensis J.R.Wheeler
  • H. hibbertioides (Steud.) J.R.Wheeler
  • H. notibractea J.R.Wheeler
  • H. rupicola (S.Moore) C.A.Gardner
  • H. sericosepala (as H. sp. Gnangara)
Similar to Hibbertia priceana, H. sejuncta also possesses stamens that are arranged all around three glabrous carpels, with two free stamens (red arrows) and three bundles of three stamens each (blue circle). Photo: Francis Nge

 

References:

Thiele, K.R. & Nge, F. (2017). Hibbertia sejuncta, a new, rare species from Western Australia, with notes on H. helianthemoides. Nuytsia 28: 115–117.

Wheeler, J.R. (2002). A revision of Hibbertia depressa and its allies (Dilleniaceae) from Western Australia. Nuytsia 15, 127–138.