Fruit development and histochemistry of Attalea microcarpa Mart. (Arecaceae-Arecoideae)

- The fruit is a fibrous pyrenarium.
- The mesocarp have three stratas, fibrous, parenchymatous and a fibro-vascular layer.
- The endocarp undergoes sclerification and fuses with the integument.
- The characteristics of the mesocarp have relevant important to taxonomy.
- The mesocarp characteristics relate to dispersal with importance as energetic reserve.

This study analyzes the morpho-anatomy of fruit development, as well as histochemical aspects of mature fruits of the Amazonian palm Attalea microcarpa. The fruit of this palm is a fibrous pyrenarium, developing from a superior ovary, with major developmental changes taking place in the mesocarp and endocarp. The mesocarp presents three strata, the first of which is fibrous and comprised of parenchyma, which differentiates during development into sclereids as well as fibrous and fibro-vascular bundles of varying widths. The second is a parenchymatous layer that differentiates and accumulates large quantities of starch grains and droplets of lipids, forming a fleshy layer. The third is a fibro-vascular layer internally attached to the endocarp. The endocarp undergoes sclerification and fuses with the integument, forming the dispersal unit. The endosperm is oily. The characteristics of the mesocarp have important relevance to taxonomy, as the arrangement of the sclereids can be a diagnostic character for the species, while the characteristics of the fleshy mesocarp are relevant to dispersal, being of great importance in presenting an energetic reserve.