Systematic study on Gondwanan plant, Podocarpus (Podocarpaceae)

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The family Podocarpaceae is composed with 17 genera and ca. 125 species (Page, 1990), and is mainly distributed in the southern hemisphere. The family Podocarpaceae is diversified in their ecological habit, and its infrafamilial classification including the circumscription of the family has been problematic. This study aims to construct a sequence database for the chloroplast encoded atpB, matK and rbcL genes in order to reconstruct a molecular phylogeny for the family and to use this phylogeny to address the circumscription of the genus Podocarpus, I.e., phylogenetic relationships among the genera of Podocarpus sensu stricto, Afrocarpus, Nageia, Decussocarpus, Retrophyllum, Parasitaxus, Prumnopytis and Sundacarpus. The genus Podocarpus is monophyletic with genera of Afrocarpus, Nageia, Decussocarpus and Retrophyllum, however, Parasitaxus, Prumnopytis and Sundacarpus are unrelated to the genus. The latter group is located on the basal clade within the family and makes a monophyletic group with genera of Lagarostrobos, Lepidothamnus, Phyllodadus, and Halocarpus. Infrageneric classification of the genus Podocarpus suggested by de Laubenfels (1969, 1985) was strongly supported by the molecular phylogeny. Morphological characteristics such as presence or absence of Florin ring on stomata and morphology of leaves were revealed to be informative characteristics for the phylogeny. The present result indicates that species of Podocarpus had already evolved into the two subgenera until Cretaceous (prior to breakup of Gondwanaland), and species of each subgenus was independently evolved in each area of the southern hemisphere.