EXTRAFLORAL NECTARIES IN EBENACEAE: ANATOMY,MORPHOLOGY, AND DISTRIBUTION

Previous superficial reports, but only one anatomical study of one species, have supported the view that extrafloral nectaries (EFNs) of the unusual Benincasa type (i.e., with several layers of small nectariferous cells) of “Flachnektarien” (surface nectary) are common in Ebenaceae. An anatomical survey was made of 107 species (24% of the 450 species) of the four genera commonly accepted (Diospyros—73, Euclea—13, Maba— 12, Royena—9). There are 1–15 abaxial EFNs per leaf (two species each of Euclea and Royena had none). They were all of the Benincasa type, subtended by an irregularly 1–2-layered sheath of cells with extremely thick radial walls. The pattern of minor vein association allowed recognition of two subtypes: apovascular (two or more subglandular layers between vein and sheath) and paravascular (one subglandular separating layer). Apovascular EFNs are smaller but more numerous per leaf, paravascular EFNs are larger but fewer per leaf. The apovascular subtype is most common in North America and Asia; a mixture of both subtypes occurs elsewhere; Euclea has only the latter subtype. Both subtypes have the most extensive vascular association yet described for Flachnektarien. They appear to have become specialized early in the family's evolution, before extensive migration occurred.