Floral structure and nectary anatomy of <i>Bertholletia excelsa</i> (Lecythidaceae)

The floral nectary of Bertholletia excelsa was studied through permanent, histological cross-sections. The flower showed two rings of androecial vascular bundles, the inner for the fertile stamens and the outer for the androecial hood. The androecial hood, originating from the abaxial side of the androecium, is a well-developed, curved, and highly unilateral structure that covers the fertile stamens and stigma. At the apex and on the inner surface of this structure, several finger-like appendages. Histological cross-sections of the androecial hood, from the distal part towards the centre of the flower, reveal that the secretory parenchyma originates in the medium of the inner-distal part of the hood. The secretory tissue is surrounded by vascular bundles that more distally supply the finger-like appendages of the androecial hood. The nectariferous parenchyma lacks internal vascular bundles and consists of small cells, starch-rich, with large vacuoles and a prominent nucleus. The nectariferous epidermis is striated. No stomata or glandular hairs were observed associated with the nectariferous epidermis. The nectary is located within the distal part of the androecial hood and can be classified as a structured, non-vascularized, androecial type. This specialization in the location of the nectar secreting tissue is linked with a complex pollination mechanism, allowing access to the reward only for large bees with long proboscis.