What Is inside a Papilionoid Flower? I. Floral Vascular Anatomy in the New Caledonian Endemic Clade Arthroclianthus-Nephrodesmus (Fabaceae, Faboideae).

Premise of research. The diversity of vascular patterns in flowers of Fabaceae subfamily Faboideae is remarkable yet remains somewhat overlooked. Here we propose an empirical examination of anatomical features of flowers of a selected group of Faboideae in which taxonomic delineation is currently being investigated in order to reassess the relevance of floral vascular characters for systematic studies. We focus on the New Caledonian endemic clade Arthroclianthus-Nephrodesmus , exhibiting contrasting flower morphologies. Methodology. Preanthetic floral buds of 6 of 17 species of the genera Arthroclianthus and Nephrodesmus were selected from herbarium specimens and a living tree. They were cut in serial transverse sections and studied with light microscopy. Pivotal results. We identify three vascular organizations in the Arthroclianthus-Nephrodesmus clade: the N. francii , A. sanguineus , and A. microbotrys patterns. The N. francii and A. sanguineus patterns both belong to the unihiate series. In the A. sanguineus and A. microbotrys patterns, the receptacle is vascularized by a similar number of traces, higher than in the N. francii pattern. We describe a very rare Faboideae vascular organization in A. microbotrys , the unihiate-dihiate series. Conclusions. The diversity of floral vascular anatomies shown by the Arthroclianthus-Nephrodesmus clade is the greatest among the 80 studied genera of Faboideae. Our results do not support the conservation of the current delineation of the two genera and are consistent with ongoing molecular investigations. The size of the flower organs could constrain vascular organization of the flowers, explaining the differences in the number of traces in the receptacle. [ABSTRACT FROM AUTHOR]