Morphology, structure, and histochemistry of the inflorescences, fruit, and seed of the Ramón nut, Brosimum alicastrum Sw. subsp. alicastrum CC Berg (Moraceae)

Abstract

Brosimum alicastrum Sw, known in Mexico as the Ramon nut, is a sustainable resource in the economy of Yucatan, Mexico; the pulp and seed are edible, and the latter is very nutritious when consumed whole or ground into corn or wheat flour to make tortillas and bread. Because the inflorescences are an essential source of Moraceae taxonomic traits, the histochemistry of the floral parts, fruit, and seed of B. alicastrum was studied to establish their structural characteristics and chemical nature. Different developmental stages of the structures were studied with anatomical and histochemical techniques and scanning electron microscopy. The species presented three achlamydeous floral morphs: (a) uniflorous, unisexual pistillate inflorescence, with the ovary embedded in the receptacle, and exposing a style with bifurcate stigma; (b) unisexual staminate inflorescence with flowers with one stamen, a straight and thick filament, a bilocular peltate anther, with fused theca and circumscissile dehiscence, characteristics that define it as Brosimum alicastrum Sw. subsp. alicastrum CC Berg; and (c) bisexual inflorescence with staminate flowers and a pistillate flower with an atrophied ovule. The fleshy and sweet pulp is derived from the receptacle containing glycoproteins and idioblasts. The endocarp, which derives from the ovary wall, has a coriaceous consistency, so the fruit is classified as a pome. Thick and unequal fleshy cotyledons with laticifers, proteinoplasts, amyloplasts, and idioblasts; endosperm is absent from the mature seed; a thin and lignified seed coat surrounds them. The nutritional characteristics of the fruit and seed were corroborated with positive reactions of histochemical techniques.