Developmental Aspects of the Shoot Apex, Leaf, and Beltian Bodies of Acacia cornigera

The final event of leaf ontogeny in Acacia cornigera is the production of a Beltian body at the tip of each rachis and pinnule. This structure serves as a food source for an ant, Pseudomyrmex ferruginea F. Smith, that lives in a mutualistic relationship with the plant. The mature Beltian body consists of an epidermis, hypodermis, cortex and central vascular bundle. Anatomical and cytohistological comparisons between the shoot apex and leaf ontogeny in A. cornigera and similar developmental aspects of the phyllode of A. longifolia Willd. and of the leaf of A. decurrens var. dealbata F.v.M. indicate that each type of photosynthetic organ is characterized by a different period of longevity of its group of sub-apical initials. The phylogenetic history of Beltian bodies is also discussed.