Evolution of the genera Vitex (Lamiaceae) and Zygogynum (Winteraceae) on New Caledonia
Pratt, S. J. (2013). Evolution of the genera Vitex (Lamiaceae) and Zygogynum (Winteraceae) on New Caledonia (Thesis, Master of Science (MSc)). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/7570
Permanent Research Commons link: https://hdl.handle.net/10289/7570
The New Caledonia archipelago is home to a richly diverse flora including a disproportionate number of lineages whose heritage can be traced to ancient Gondwana. Much of this species richness is owed to the complex geologic history, including an extensive period of submersion, of the region which actively shaped the flora over millennia. Given such complexity there is always unknowns both with regards to the circumscription of such a diverse flora and to understanding aspects of the archipelagos geologic past, which in many cases prove extremely difficult to resolve. This thesis investigates two aspects of this notion using modern day molecular techniques. The first aspect that we investigate is the question of species circumscription with regards to Vitex (Lamiaceae). Here we scrutinize the monophyly of the morphologically variable species Vitex collina, as described by Mabberley (1990), previously suggested by Mabberley to comprise a minimum of three distinct morphotypes. Additionally we consider the genetic uniqueness of a recently discovered species, tentatively named Vitex sp. “unifolia”, from currently accepted New Caledonian Vitex collina s.l. Maximum likelihood (ML) analyses using the internal transcribed spacer (ITS) genetic loci revealed that New Caledonian Vitex collina is paraphyletic with New Zealand V. lucens and Australian V. lignum-vitae nested within a well-supported V. collina s.l. clade. Our results suggest a minimum of two genetically distinct entities within V. collina, though the new species Vitex sp. “unifolia” was not distinguished genetically from Vitex cf. “collina”. The additional morphological analysis in light of our molecular analyses revealed further distinction of taxa within our sample group. This revealed a potential for three separate morphological entities within Vitex collina s.l. specimens, with Vitex sp. “unifolia” representing a fourth. Further research will result in the formal recognition of Vitex sp. “unifolia” upon publication, as well as further delimitation of the distinct entities within V. collina s.l. These revisions will have implications for the conservation status of these revised species, especially with regards to the rare Vitex sp. “unifolia”. The second aspect investigated New Caledonian Winteraceae focussing on two research aims. The first aim scrutinised the New Caledonian Zygogynum s.l. in light of revisions made in Vink (1988; 1993; 2003), where four previously recognised genera (Belliolum, Bubbia, Exospermum, and Zygogynum) were dismantled into a single broadly circumscribed genus. The second aim was to assess any major morphological trends within Zygogynum s.l. and biogeographic patterns within the Winteraceae. Maximum Likelihood and Bayesian analyses using the internal transcribed spacer (ITS) and psbA-trnH genetic loci confirmed the monophyly and position of Takhtajania, Tasmannia, Drimys, and Pseudowintera within the Winteraceae. New Caledonian Zygogynum s.l. was shown to be paraphyletic with Z. schlechteri nested within a distinct Australian Bubbia clade separate from remaining Zygogynum. Our analyses showed no support for the distinction of species previously belonging to Belliolum and Exospermum with all remaining Zygogynum forming a monophyletic clade. The monophyly of species within the Zygogynum were for the most part resolved, with only few species left unresolved or paraphyletic relationships. Further investigation of biogeography within the Winteraceae revealed that Zealandic Winteraceae share their common ancestor with South American taxa, reflecting the Gondwanic roots of this family, with Australian Bubbia having originated from New Caledonian Zygogynum. From this we suggest, upon further investigation, that the retention of Bubbia within Zygogynum s.l. was supported and should be maintained. Alternately, if Bubbia is maintained as distinct from Zygogynum s.l., Z. schlechteri will be revised to Bubbia schlechteri. Further research including specimens of all described taxa will improve the resolution of our analyses, likely identifying further inconsistences that require revision or attention. Our investigation into morphological trends within the Zygogynum uncovered a trend of carpel evolution, in which a single well supported clade of Zygogynum exhibit fused carpels with all others within the family exhibiting unfused gynoecia. The significance of this is that it is a derived trait recognised as a reoccurring trend within the Angiosperm lineage, though this is the first instance where it has been identified occurring within a single genus.
University of Waikato
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