The morphology and relationships of oncotheca balansae1

TLDR: The anatomy and morphology of vegetative and reproductive structures of the monotypic, dicotyledonous genus Oncotheca were studied and support is given to the elevation of the genus to familial status and its placement near the Theaceae.

Abstract: The anatomy and morphology of vegetative and reproductive structures of the monotypic, dicotyledonous genus Oncotheca were studied to evaluate the svstematic relationships of this New Caledonian endemic. Wood has remained at a low level of advancement, as evidenced by the solitary, angular pores and exclusively scalariform perforation plates. Imperforate tracheary elements are fiber tracheids, and asial parenchyma is diffuse to diffuse in aggregates in distribution. Sieve tube elements possess oblique to very oblique, compound sieve plates. Nodal anatomy is pentalacunar, and petioles contain a single, undissec.ted arc of vascular tissue. A number of apparently xeromorphic leaf features, including general foliar coriaceousness, may result from the poor availability of soil minerals. Leaves are characterized by a thick cuticle, uniseriate epidermis with nearly anomocytic stomata having paracytic or tetracytic tendencies and a bifacial mesophyll with two or three hypodermal layers. Foliar venation is brochidodromous. Highorder venation is characterized by freely ending branched veinlets and imperfect areolation. Flowers are relatively advanced, as evidenced by extensive fusion of parts and the tlnion of major floral bundles such as the ventral carpellary traces. A c]ose relationship between Oncotheca and the Aquifoliaceae and Ebenaceae is refuted. Support is given to the elevation of the genus to familial status and its placement near the Theaceae.