Chrissen Gemmill*, Steven Pratt, Jérôme Munzinger, Porter Lowry II, Nick Demetras
The oceanic islands of New Zealand and New Caledonia are cut from much the same
cloth: they are both off cast fragments of Gondwana, have endured dynamic and
transformative geological processes including periods of submergence, and have
been isolated from any other landmasses in the southern Pacific ocean for similar
time frames. Furthermore, these islands are intimately connected as they both rest
upon the sunken former continent of Zealandia (Fig 1). Evidence of this shared
history is reflected by the numerous flowering plant families that are found on both
of these sister- archipelagos. This study focuses on the evolution of the iconic plant
family Winteraceae of Zealandia, and specifically on the sister genera Pseudowintera
and Zygogynum (sensu lato). Winteraceae are an ancient, mostly Southern
Hemisphere angiosperm family of evergreen trees, known for their vessel-less
wood, peppery scent, remarkable flowers and excellent fossil record.
Fig 1. Zealandia
Winteraceae are represented in New Zealand by a single genus Pseudowintera
(horopito) with four extant endemic, well-known species. The case is quite different
for the New Caledonian taxa, which reveal a complex taxonomic history. The most
recent revisions by Vink were highly radical, placing all members of four previously
recognized genera into a single broadly defined genus Zygogynum (Fig 2.)
comprising 18 endemic species, within which he also recognized 13 subspecies and 3
varieties for a total of 30 taxa. It is not clear whether the characters used to delimit
these infraspecific entities are constant or if they are phenotypically plastic and
hence taxonomically artificial and uninformative.
Fig 2. Zygogynum
To test Vink's taxonomic hypotheses and resolve relationships among these taxa, we
have sampled Zealandic taxa comprehensively and used both nuclear (ITS) and cpDNA
(psbA-trnH)
sequence
variation.
ITS only analysis:
Subset ITS + cpDNA:998 characters, 896 constan, 63 parsimonyinformative, 39 autapomorphic characters; GTR+Γ+I
Insert full ITS tree and ITS+cpDNA trees here.
• Preliminary analyses suggest that Zygogynum is not monophyletic with Z.
amplecicaule (including all currently recognized infraspecific taxa) sister to
Pseudowintera and the remaining Zygogynum taxa. Within the large Zygogynum
clade, some species are resolved as monophyletic (e.g., Z. comptonii), while many
remain paraphyletic. Overall our analyses suggest that revision of this genus is
required.
• We observed the evolutionary trend from free carpels to fused carpels within this
single genus
• In addition to a revised taxonomic treatment and reconstructed biogeographic and
evolutionary scenarios, our work will contribute important new information relevant
to the on-going debate about the extent and duration of the Oligocene drowning of
New Zealand and help address a much-debated question regarding the origin of
these taxa: are they continuously inhabiting ancient lineages or is their modern
presence the result of more recent long-distance dispersal?