Systematics and evolution of Archidendron, the largest group of tropical legumes in the Austral region (APSF 14/4)

APSF 14/4 | Amount: $ 44,375 | Project Leader: G Brown | Project Period: Jul 2014 - Jul 2017

A project undertaken at the School of Botany, The University of Melbourne, and supervised by Gillian Brown

Background

Archidendron is the largest group of Old World Ingeae (Leguminosae; Mimosoideae; Ingeae) occurring in Australian, New Guinean, and SE Asian lowland rainforests. It includes 94 species, at least 22 of these are listed as imperfectly known, which are placed into eight series. The genus is in need of critical revision and raises many interesting ecological and evolutionary questions. Preliminary phylogenetic results, based on limited sampling from tribal level studies, suggest that Archidendron is not monophyletic. Two geographic clades associated with Wallace’s line are identified and they are not closely related. Should this be one or two genera? Some species have ants living in their hollow leaf rachis and stems; has this ant association arisen in a single or multiple lineages? Some taxa have notable geographic disjunctions (Figure 1), including series Morolobiae (Maluku, N QLD, NSW/QLD border), A. hendersonii (N QLD, NSW) and A. grandiflorum (S New Guinea, QLD, NSW). Do these species disjunctions correlate with geographic barriers, corridors or refugia identified for other taxa? Did the Australian tropical rainforest legume trees originate in Australia or have they arrived more recently from Asia, via Malesia?

Figure 1. Phylogeography distribution map
Figure 2. Phylogeographic summary of genetic data for two species of Archidendron. IBRA regions are colour coded over the distribution maps for both species. Graph of calyx and corolla lengths for Archidendron hendersonii is also shown.
Aims

This research aims to produce a robust, multiple gene phylogeny of Archidendron with integration of morphological characters; investigate phylogeographic history of north-eastern Australian rainforest taxa; and review the taxonomy of a widespread vulnerable Australian taxon: A. hendersonii.

Results

This study has produced the most comprehensive phylogeny of Archidendron, using the targeted amplicon next generation sequencing method.  Morphological character reassessment of the two clades of Archidendron and related taxa have allowed us to critical revise taxon boundaries to reflect evolutionary lineages, contributing to documenting the biodiversity of the Old World tropics, focused on Australia and New Guinea.

The morphological and genetic variation in the vulnerable disjunct Australian taxon Archidendron hendersonii has uncovered a small flowered northern form that is also more pubescent than the southern specimens (Figure 2).
Comparative analyses of three rainforest taxa (Archidendron grandiflorum, A. hendersonii and Pararchidendron pruinosum) are investigating the phylogeographic history of north-eastern Australian rainforest taxa to improve our understanding of the history of flora in rainforests of Australia and New Guinea.  Results show a strong connection between individuals from the Cape York Peninsula and the Wet Tropics, with multiple connections from the Wet Tropics to central and southern Queensland.