Ontogenesis of the winged oleaginous seeds of Magonia pubescens (Sapindaceae)

- The ontogenesis of the winged and oleaginous seed was described.
- The seed wing originates from the lateral expansion of the testa.
- The seed core is coated with an unusual hygroscopic layer.
- The nucellus is proliferative and secretory.
- The seed structures have taxonomic and adaptive value to the Cerrado.

Magonia pubescens is a common native tree species of the Cerrado biome (neotropical savanna) with potential for biofuel production. We describe the ontogenesis of the oleaginous seed of this species and development of its wing and unusual mucilaginous layer. Ovaries and seeds were accompanied throughout their development using standard methods of plant anatomy; the cotyledons were examined using transmission electron microscopy. The wing consists of two juxtaposed layers formed by lateral expansion of the testa. The seed core is composed of three layers, with the outer layer being highly hygroscopic. A conspicuous raphe surrounds the embryo in the median longitudinal plane, and the nucellus is proliferative and secretory. The embryo is oleaginous and late-maturing. Seed development requires approximately 350 days and takes place in seven phases: (1) ovule fertilization; (2) raphe differentiation; (3) wing expansion; (4) differentiation of the seed coat layers; (5) embryo expansion; (6) maturation of the wing and the mucilaginous layer; and, (7) accumulation of mucilage in the core and oil in the embryo. The winged seeds of M. pubescens have complex structures and important adaptive features such as the mucilaginous core and raphe, which contribute to hydration during germination, as well as abundant oil reserves in the embryo that aid seedling establishment. These seeds structure contribute to the reproductive success of this species and its adaptation to the highly seasonal Cerrado biome.

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