Systematics and evolution of Archidendron, the largest group of tropical legumes in the Austral region

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

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?

This study will be the most comprehensive phylogeny of Archidendron attempted, building on our preliminary molecular analyses and plant collections. New analyses will use next generation sequencing methods, and results will allow critical evaluation of taxon boundaries and contribute to documenting the biodiversity of the Old World tropics, focused on Australia and New Guinea. Understanding the genetic diversity and relationships of taxa of Archidendron will provide invaluable information on phylogeographic patterns in the rainforests of eastern Australia, which are not well documented for the flora, and identify historical biogeographic patterns within the SE Asian, Australian and Pacific region. Awareness of these historical patterns has implications for management and conservation of plant diversity in the region, including the Australian Wet Tropics, a world heritage area

The aims of our study are to:

  1. Produce a robust, multiple gene phylogeny of Archidendron with integration of morphological characters to assess evolutionary lineages to:
    1. investigate biogeographic patterns and diversification of legumes in Australia and SE Asia
    2. revise taxonomy to reflect evolutionary lineages.
  2. Investigate 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.
  3. Assess morphological and genetic variation in the vulnerable disjunct Australian taxon Archidendron hendersonii to revise taxonomy which shows considerable variation in flower size.
Figure 1. Phylogeography distribution map

Figure 2. Archidendron lucyi fruit

Figure 3. Archidendron lucyi fruit and flowers

Figure 4. Exapmles of Archidendron glands