Divergence, diversity and species of the Australasian Callitris (Cupressaceae) and allied genera: evidence from ITS sequence data

Abstract

Callitris Vent. is the most speciose of the Southern Hemisphere genera of Cupressaceae, occupying a diverse range of habitats within Australia and New Caledonia and is closely allied to Actinostrobus Miq. and the monotypic New Caledonian genus Neocallitropsis Florin. Results of phylogenetic analyses of 18S–26S rDNA internal transcribed spacer region sequences for representatives of 12 of the 18 currently recognised species of Callitris, two of the three Actinostrobus species and the single known species of Neocallitropsis help to clarify major lineages and relationships in this group. ITS data provide strong evidence against the monophyly of Callitris as currently circumscribed, with the strongest evidence being for the inclusion of the New Caledonian monotypic species Neocallitropsis pancheri (Carriere) de Laubenfels. This species shares a close relationship with C. sulcata (Parl.) Schltr. Three representatives of Actinostrobus are monophyletic and are placed in a polytomy with C. drummondii (Parl.) F.Muell., although indels provide some support for the early divergence of Actinostrobus in this group. Remaining sampled members of Callitris form a weakly supported clade, with C. macleayana (F.Muell.) F.Muell. sister to a highly robust core Callitris. Relationships within this core Callitris are unresolved; however, the following seven lineages are supported: C. rhomboidea R.Br. ex Rich.; C. muelleri (Parl.) F.Muell., C. oblonga Rich. and C. endlicheri (Parl.) F.M. Bailey; C. gracilis R.T. Baker, C. glaucophylla Thompson & Johnson and C. tuberculata R.Br. ex R.T. Baker & Smith; C. intratropica Baker & Smith; and C. columellaris F.Muell. There has been a marked increase in the rate of divergence of ITS sequences during the evolution of those populations assigned to C. intratropica, which perhaps reflects speciation processes within this widely distributed group.