Phylogeny, biogeography and adaptive radiation of Pachycladon (Brassicaceae) in the mountains of South Island, New Zealand

Abstract

Aim To report analyses and propose hypotheses of adaptive radiation that explain distributional patterns of the alpine genus Pachycladon Hook.f. – a morphologically diverse genus from New Zealand closely related to Arabidopsis thaliana. Location South Island, New Zealand. Methods Morphological and nrDNA ITS sequence phylogenies were generated for Pachycladon. An analysis is presented of species distributional patterns and attributes. Results Phylogenetic analyses of morphological characters and nrDNA ITS sequence data were found to be congruent in supporting three New Zealand clades for Pachycladon. Monophyletic groups identified within the genus are geographically distinct and are associated with different geological parent materials. Distribution maps, latitude and altitude range, and data on geological parent material are presented for the nine named and one unnamed species of Pachycladon from New Zealand. Main conclusions (a) Panbiogeographic hypotheses accounting for the origin and present‐day distribution of Pachycladon in New Zealand are not supported. (b) Species diversity and distributions of Pachycladon are explained by a Late Tertiary–Quaternary adaptive radiation associated with increasing specialization to geological substrates. Pachycladon cheesemanii Heenan & A.D.Mitch. is morphologically similar to the closest overseas relatives. It is a geological generalist and has wide latitudinal and altitudinal ranges, and we suggest it resembles the ancestral form of the genus in New Zealand. Pachycladon novae‐zelandiae (Hook.f.) Hook.f. and P. wallii (Carse) Heenan & A.D.Mitch. are a southern South Island group that predominantly occurs on Haast Schist, are polycarpic, have lobed leaves, and lateral inflorescences. Pachycladon enysii (Cheeseman) Heenan & A.D.Mitch., P. fastigiata (Hook.f.) Heenan & A.D.Mitch., and P. stellata (Allan) Heenan & A.D.Mitch. are restricted to greywacke in the eastern South Island, and are facultatively monocarpic, have serrate leaves, and stout terminal inflorescenes. (c) Present distributions of Pachycladon species may relate to Pleistocene climate change. Pachycladon enysii reaches the highest altitude of New Zealand species of Pachycladon and is most common in the Southern Alps in Canterbury. We propose that this species survived on nunataks at the height of the last glaciation. In contrast, P. fastigiata grows at a lower altitude and is absent from the high mountains of the Southern Alps. We suggest it was extirpated from this area during the last glaciation.

Systematics and phylogeny of the Brassicaceae (Cruciferae): an overview

“…Mummenhoff andHurka 1994, 1995;Price et al 1994Price et al , 2001Al-Shehbaz 1997, 2003;Al-Shehbaz et al 1999;Koch et al 1999aMitchell and Heenan 2000;Al-Shehbaz and O'Kane 2002a;Heenan and Mitchell 2003;Heenan et al 2002;Beilstein et al 2006). These molecular studies strongly support the close relationship among these genera.…”

Gender dimorphism inPachycladon stellatum(Brassicaceae)

“…This ratio is low and infers selfing, but these authors concluded the flower morphology is consistent with outcrossing and the species is therefore regarded as having a mixed mating system. This second record of gender dimorphism in Pachycladon is of significance in that P. wallii and P. stellatum belong to different species groups and are not sister species in the phylogenetic analyses Heenan & Mitchell 2003). P. stellatum is monocarpic, has stout terminal inflorescences, toothed lanceolate leaves, restricted to greywacke substrate in northern South Island (inland Marlborough), and related to other greywacke species such as P. fastigiatum and P. enysii.…”

“…Of interest in regard to the general biology of P. stellatum is that it has a restricted distribution and occurs in small and scattered populations and few, if any, plants will flower at one time (Heenan & Mitchell 2003). During five field trips into the upper Awatere River catchment and Yeo Stream between 1997 and 2011 only eight populations of P. stellatum have been located and these comprised approximately 2, 3, 5, 5, 6, 6, 8, and 35 plants (Heenan & GarnockJones 1999;unpubl.…”

Five new species of Corybas (Diurideae, Orchidaceae) endemic to New Zealand and phylogeny of the Nematoceras clade

“…Some of these dispersal events have provided the ancestral stock for several plant radiations now found in sub-alpine and alpine areas of the country (Lockhart et al 2001, Meudt et al 2015. Mountain systems are of recent origin in NZ (4-2 Myr), and their formation created new habitats that facilitated diversification of several plant groups (Lockhart et al 2001, Heenan & Mitchell 2003, Winkworth et al 2005. Conversely, lowland habitats are geologically older, and species radiations are seemingly absent.…”