Reconstructing the species phylogeny of Pseudopanax (Araliaceae), a genus of hybridising trees Leon R. Perrie * , Lara D. Shepherd 1 Museum of New Zealand Te Papa Tongarewa, P.O. Box 467, Wellington, New Zealand article info Article history: Received 25 November 2008 Revised 19 April 2009 Accepted 28 May 2009 Available online 14 June 2009 Keywords: Pseudopanax Hybridisation, gene-flow, and introgression Phylogeny AFLP DNA-fingerprinting Chloroplast DNA sequences Araliaceae Neopanax Trees New Zealand abstract Pseudopanax (Araliaceae) comprises 12 tree species of diverse morphology and ecology, and is endemic to New Zealand. It is notable for the hybridisation that occurs between P. crassifolius and P. lessonii, which have very different leaves and habits. To provide context for the study of this hybridisation and other investigations, we examined the phylogeny of Pseudopanax using chloroplast DNA sequences (c.5900 base-pairs) and AFLP DNA-fingerprinting. Both approaches resolve two principal groups within Pseudo- panax – the Arboreus group and the Crassifolius + Lessonii union – but how they are related to other gen- era remains unclear. There is, nevertheless, little compelling evidence against the monophyly of Pseudopanax, making unnecessary the recent re-segregation of the Arboreus group as Neopanax. The chlo- roplast data provided minimal additional resolution, although the position of P. linearis was discordant compared to other data. Analyses of the AFLP data strongly recovered each species, aside from the mor- phologically heterogeneous P. colensoi, and the two mainland species (P. arboreus and P. crassifolius) that each contained a nested island-endemic (P. kermadecensis and P. chathamicus, respectively). However, relationships amongst species within the two principal groups were poorly resolved. An example was the uncertainty of whether P. crassifolius grouped with P. lessonii and its allies, or the morphologically similar species it had been previously placed with. This in turn raises the issue of how hybridisation might affect phylogenies and the ability to reconstruct them, even when using multiple, independent markers. Ó 2009 Elsevier Inc. All rights reserved. 1. Introduction An understanding of phylogeny, or how species are related to one another, facilitates a more comprehensive interpretation of evolutionary processes, including speciation and hybridisation (Harrison, 1998). The latter two themes are intertwined because it is believed that the study of hybridising species can reveal the factors maintaining species’ boundaries, which in turn may be informative as to what is initially important in speciation (Harri- son, 1993; Lexer et al., 2005). Recent studies indicate that signifi- cant hybridisation and introgression following speciation may be common, and that the genetic basis for isolation may be very small, with much introgression occurring amongst parts of the genome not tightly linked to these isolating genetic elements (Hey, 2006; Yatabe et al., 2007). It is widely recognised (e.g., Rieseberg and Sol- tis, 1991) that introgression can lead to discordance between the phylogeny inferred from a single locus (i.e., a ‘gene-tree’) and that inferred from multiple independent characters (i.e., the ‘species- tree’). Consequently, phylogenies are being increasingly recon- structed using multi-locus genetic markers, but there has been lit- tle exploration of how such phylogenetic inferences might be affected by introgression, and, in turn, what this means for using them to interpret hybrid zones. Furthermore, studies of hybridisa- tion involving species with a broader range of demographic, eco- logical, and reproductive characteristics are required before patterns and processes can be widely generalised. A striking example of hybridisation occurs in Pseudopanax (Aral- iaceae). The circumscription of this genus is historically complex, and still contentious (see below). Based largely on the results of Mitchell and Wagstaff (1997, 2000), we regard Pseudopanax as comprising the species listed by Philipson (1965), but with the addition of P. macintyrei (Wardle, 1968), and the exclusion of non-New Zealand species and the species subsequently referred to Raukaua (Mitchell et al., 1997). So defined, Pseudopanax is ende- mic to New Zealand and constitutes 12 small trees or large shrubs, that are dioecious (Webb et al., 1999), and range from coastal to subalpine habitats. Extraordinary hybridisation occurs between P. crassifolius (lancewood, horoeka) and P. lessonii (coastal five-finger, houpara), in that (1) their leaves (Fig. 1) and habit (see below) are very different; (2) their hybrids are morphologically diverse (see Fig. 1 for examples of hybrids’ leaves); (3) hybridisation occurs at 1055-7903/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.ympev.2009.05.030 * Corresponding author. Fax: +64 4 381 7070. E-mail address: leonp@tepapa.govt.nz (L.R. Perrie). 1 Present address: Allan Wilson Centre, Massey University, Palmerston North, New Zealand. Molecular Phylogenetics and Evolution 52 (2009) 774–783 Contents lists available at ScienceDirect Molecular Phylogenetics and Evolution journal homepage: www.elsevier.com/locate/ympev