ARTICLE IN PRESS Organisms, Diversity & Evolution 5 (2005) 237–247 www.elsevier.de/ode Evolution of the New Zealand mountain flora: Origins, diversification and dispersal RichardC. Winkworth a,Ã, Steven J. Wagstaffb, DavidGlenny b, Peter J. Lockhartc aDepartment of Ecology and Evolutionary Biology, Yale University, P.O. Box 208105, New Haven, CT 06520-8105, USA bManaaki Whenua Landcare Research, P.O. Box 69, Lincoln 8152, New Zealand cThe Allan Wilson Centre for Molecular Ecology and Evolution, Massey University, Private Bag 11222, Palmerston North, New Zealand Received11 May 2004; accepted16 December 2004 Abstract The New Zealand mountains provide a unique system in which to study the evolution of alpine plants. The relationship between the recent uplift of mountain habitats (5–2 million year ago (mya)) andfloristic diversity has polarizedhypotheses on the evolution of the alpine flora; suggestions have rangedfrom an ancient history in New Zealand to recent arrival by long distance dispersal from the Northern Hemisphere. Molecular phylogenies are now available for numerous New Zealandalpine plant groups andthese provideinsights into the evolution of this unique flora. Taken together with the fossil record, these studies suggest that many alpine lineages first arrived in New Zealand during the late Tertiary and subsequent radiations accompanied environmental upheaval in the Pliocene and Pleistocene. Ongoing studies are investigating the processes that contribute to morphological and ecological diversity in the New Zealandalpine flora. r 2005 Gesellschaft fu¨ r Biologische Systematik. Publishedby Elsevier GmbH. All rights reserved. Keywords: Biogeography; Dispersal; Ecological diversification; Morphological radiation; New Zealand alpine flora Introduction The New Zealandbiota has developedonan ancient continental landmass that was progressively isolated ‘‘With regardto general problems of biogeography, during the late Cretaceous and early Tertiary. Originally the biota of New Zealandhas been, perhaps, the most linkedto the Gondwanan supercontinent, New Zealand important of any in the world. It has figured promi- has been separatedfrom its closest continental neighbor, nently in all discussions of austral biogeography, and all Australia, by 2000 km for the last 60 million years (my). notable authorities have felt obligedto explain its The long isolation of New Zealandis reflectedin the history: explain New Zealandandthe worldfalls into generally oceanic character of its biota, andin this place aroundit’’ ( Nelson 1975). respect it is similar to Hawaii andthe Gala ´ pagos. However, New Zealandhas a much olderheritage than these strictly oceanic archipelagos, with a long pre- ÃCorresponding author. Tel.: +1 (203) 436 4992; history of dramatic environmental change that has fax: +1 (203) 432 3854. helpedshape its biota. More complex than most oceanic E-mail address: [email protected] (R.C. Winkworth). islands yet more tractable than many continental 1439-6092/$ - see front matter r 2005 Gesellschaft fu¨ r Biologische Systematik. Publishedby Elsevier GmbH. All rights reserved. doi:10.1016/j.ode.2004.12.001 ARTICLE IN PRESS 238 R.C. Winkworth et al. / Organisms, Diversity & Evolution 5 (2005) 237–247 systems, New Zealandprovidesunique opportunities to study evolution. The biogeographic history of New Zealandhas, as Nelson (1975) points out, attractedthe attention of many biogeographers. In this regard, the flora of its mountains (referredto here as the alpine flora) has been one of the most extensively studied elements. However, despite numerous detailed studies and several syntheses, hypotheses about the origins anddiversification of the New Zealandmountain flora have remainedpolarized– largely due to contrasting views on the relative importance of dispersal, geological change, and climatic fluctuations (McGlone et al. 2001). Recent advances in our knowledge of New Zealand’s geological and climatic history, andphylogenetic studies for a growing number of lineages have provided important insights into the origins andevolution of the alpine flora. In this review we have two goals: (i) to discuss insights from recent molecular phylogenetic studies, and (ii) to highlight Fig. 1. Extent of alpine areas in New Zealandandalpine plant distribution patterns. Areas above alpine tree line are indicated avenues for future research. As a framework for this as black silhouettes; montane habitats are more extensive, discussion, we first briefly summarize the alpine setting especially in the North Island. Gray lines indicate generalized in New Zealandandbiogeographic hypotheses concern- boundaries for two endemic-rich centers and an intervening ing the alpine flora. endemic-poor gap. Several individual mountains or mountain ranges described in the text are marked. There is little doubt that mountains are a geologically Discussion recent feature in New Zealand. For much of the last 85 my New Zealandhas been an isolatedlandmass of The New Zealand mountains limitedtopographic relief. Having broken away from Gondwana in the late Mesozoic, New Zealand con- Mountains dominate much of the New Zealand tinuedto separate from Australia until the early landscape. With the exception of the central North Paleocene. Throughout the late Cretaceous andearly Islandvolcanoes, the alpine zone is restrictedto a single, Tertiary the ancestral New Zealandlandmass suffered ruggedmountain chain that extendsfrom Stewart Island steady erosion. By the latest Oligocene only a scattered in the south, along the Southern Alps of the South archipelago of low-lying islands remained (Cooper and Island, and through the North Island to East Cape Cooper 1995). The general form of contemporary New (Fig. 1). Although largely contiguous, the New Zealand Zealandis the result of tectonic uplift that began axial mountains vary considerably in geomorphology, approximately 25 million year ago (mya) with the with five regions recognizedbasedon the underlying activation of the modern Pacific-Australian plate parent material. For example, the eastern mountains of boundary (Cooper et al. 1987; Kamp 1992). Miocene the Southern Alps (e.g., the Craigieburn Range) are tectonism ledto rapidchanges in distribution and composedof greywacke andargillite rocks. These topography, but the general uplift trendresultedin a formations underwent complex faulting during their narrow, elongate landmass of rugged relief. It was not uplift andare highly prone to frost shattering that until the Pliocene (5–2 mya) that the formation of the results in the extensive talus andscree slopes Alpine Fault system andthe increasing tempo of characteristic of this region. In contrast, folding and tectonic activity ledto the rapidelevation of the axial tilting of crustal sections formedthe Otago mountains in New Zealand( Ollier 1986; Cox and mountains (e.g., the OldMan Range). These Findlay 1995; Batt et al. 2000). Although the overall more rounded, undulating mountains are composed of form of these mountains reflects the original pattern of harder schist rocks and were not subjected to tectonism, many details of the contemporary relief are extensive glacial erosion (Holloway 1982; Whitehouse the result of extensive modification following uplift. In andPearce 1992 ). Such geological differences, as particular, the alpine landscape of the South Island was well as striking differences in past and present heavy modified by glaciation during the latest Pliocene climates, have resultedin a diversearray of habitat andPleistocene. From about 2.5 mya large areas of the types in the New Zealandmountains ( Whitehouse and Southern Alps were repeatedly glaciated, and many Pearce 1992). contemporary landforms relate directly to glacial ARTICLE IN PRESS R.C. Winkworth et al. / Organisms, Diversity & Evolution 5 (2005) 237–247 239 modeling or modification of glacial constructions. 1978). In contrast, Wardle (1963) and Fleming (1963) Although glaciation was more limitedin the North speculatedthat Tertiary New Zealandwouldnot have Island, cold climate processes, such as periglacial mass provided suitable environments for cool temperate movement, have strongly influencedlower North Island plants. Insteadthey suggestedthat ancestors of modern landscapes (Beu and Edwards 1984; McGlone 1985; alpine lineages may have spent this periodin cool Suggate 1990; Pillans et al. 1992; Markgraf et al. 1995). temperate areas to the south of New Zealand, re- Post-glacial erosion has also playedan important role in establishing in New Zealandonly after suitable habitats shaping the modern alpine landscape (Suggate 1990; became available in the late Pliocene andPleistocene. Pillans et al. 1992). Wardle (1963) hypothesizedthat a southern extension to The most distinctive North Island mountains are the New Zealand(or perhaps islandsto the south; see four volcanic peaks, three on the Central Plateau (Mt. Dawson 1988) wouldhave providedcool climates, Ruapehu, Mt. Ngauruhoe, andMt. Tongariro) andone to whereas Fleming (1963) favoredAntarctica as a the west (Mt. Taranaki). These mountains are younger potential refuge for cool-adapted lineages. than those of the axial ranges, having reachedtheir present A link between the New Zealandalpine flora and elevations during the last Pleistocene glacial or more floras of the northern temperate zone has long been recently. Their contemporary relief has been shapedby recognized. For example, in an analysis by Dawson both volcanic activity anderosion ( Holloway 1982). (1963) genera with north temperate affinities formedthe largest component of