Carpel – Fruit in a Coniferous Genus Araucaria and the Enigma of Angiosperm Origin

Abstract

Reproductive morphology of araucarian samara is revised revealing a carpellate structure of the stone. In A. columnaris it is formed by a supercoiled spermophyll (‘seed scale’), with a stigmatic apical lobe. This structure is analogous to the ‘classical’ peltate carpel of flowering plants. Stone opens with two apical pores. Pollen germinates on the apical stigmatic crest, with extracellular matter exuded from a stigmatic gland and its opposite on the bract apophysis. Ovulate structures are of the same basic type in the allied genera Wollemia and Pararaucaria. Neither of these genera is morphologically ‘transitional’ at the generic as well as familial levels thus setting araucarians apart from the rest of conifers no longer conceivable as a uniquely derived clade of gymnospermous plants. Araucarians thus deserve the status of a separate order anticipating the major evolutionary advancements of angiospermy in flowering plants.