Molecular Systematics of Syzygium and Allied Genera (Myrtaceae): Evidence from the Chloroplast Genome

With as many as 1000 included species, Syzygium s.l. (including Syzygium and segregate genera such as Acmena, Acmenosperma, Cleistocalyx, Piliocalyx, and Waterhousea) comprises one of the major lineages within Myrtaceae, and is an important component of the Old-World tropical rainforest flora. As with other large genera, high species richness, an extensive distribution and relative homogeneity in morphology have hindered attempts to divide Syzygium s.l. Here, we investigate higher level relationships within the group, using parsimony and Bayesian analyses of cpDNA sequences from the matK and ndhF genes and the rpl16 intron, generated for a total of 87 species from the Syzygium group and eight outgroup taxa. Within the ingroup, four major well supported clades are found, which form a basal polytomy along with S. wesa and monotypic Anetholea. Generally, the molecular data provide little support for traditional divisions of Syzygium s.l., and the recognition of segregate groups such as Acmena, Acmenosperma, Cleistocalyx, Piliocalyx and Waterhousea. While homoplasy amongst morphological characters has misled attempts to divide the group, detailed and critical assessments of placental, ovular and seed morphology may provide novel insights into evolutionary relationships, and are an important future step in the development of a sound higher level taxonomy for Syzygium s.l.