Anatomy and fruit development in Schinopsis balansae (Anacardiaceae)

Schinopsis balansae Engl. is a dioecious tree; reproduction is by woody samaras containing a single seed. Fruit set is high, even in isolated trees, empty fruits are frequent and account for a high proportion of the total fruit production. To describe the anatomy and the ontogeny of seeded and seedless fruits, flowers and fruits at different development stages from bagged and pollen exposed flowers were studied. The development and the anatomy of the pericarp in seeded and parthenocarpic fruits did not differ. It consisted in an exocarp formed sensu lato from the external epidermis of the ovary and some layers of the underlying parenchyma. The mature mesocarp was constituted by a sclerified tissue and lysigenous channels. The fruit is of Anacardium type: the endocarp presented three sclerenchymatic and a crystalliferous layer. The endocarp development was also sensu lato because it was formed from the epidermis and the hypodermis of the carpel. This organization agrees with the only species described in the genus: S. haenkeana Engl. Schinopsis balansae is able to produce parthenocarpic fruits in the absence of pollination. Empty fruits from free exposed flowers presented embryos arrested at different stages, although total absence of an embryo was the most common condition. Parthenocarpy seems to be a plesiomorphic trait within the Anacardiaceae, but regardless of its origin, the maintenance of empty fruit production in a wind-dispersed samara is difficult to explain. Whether parthenocarpy has an adaptive value, or is an evolutionary constraint remains unclear in Schinopsis. Schinopsis balansae Engl. es un árbol dioico, cuya reproducción se realiza a través de sámaras uniseminadas. La producción de frutos es muy alta y una gran proporción de los mismos son vanos. Con la finalidad de describir la anatomía y ontogenia de los frutos, con y sin semillas, se trabajó con flores y frutos en distintos estados de desarrollo. Se utilizaron inflorescencias femeninas expuestas y embolsadas. El pericarpo de frutos con semilla y partenocárpicos presenta el mismo desarrollo y anatomía: está constituido por un exocarpo formado sensu lato a partir de la epidermis externa del ovario y algunas capas del parénquima subyacente. El mesocarpo maduro está constituido por esclerénquima y canales lisígenos. Por las características del endocarpo, este fruto se clasifica como tipo Anacardium, presentando tres estratos esclerenquimáticos y uno cristalífero. El desarrollo del endocarpo también es sensu lato, ya que deriva de la epidermis e hipodermis del carpelo. Esta anatomía concu