Ontogenesis of ovary and fruit of Acianthera johannensis (Pleurothallidinae, Orchidaceae) reveals a particular female embryology

We carried out an investigation on the female ontogenesis of Acianthera johannensis, a species with partial self-incompatibility, aiming to report the typical development of ovule and seed. We describe here the development of ovary and fruit after cross-pollination and record the time between pollination and seed formation. In this species, we verify the formation of triads of megaspores and five-nucleate megagametophytes, a very rare association in orchids. The species presents anatropous, tenuinucellate and bitegmic ovules, characters recorded for most of the orchids. Fertilization occurred 40 days after pollination, however some ovules were observed in early stages of development even in fully developed fruits. Our data indicate that unfertilized ovule can be found in mature fruits, reinforcing the hypothesis that these could be the structures often referred in the literature as seeds without embryos. This information is important to the following studies that aim to clarify the mechanism involved in the formation of structures without embryo observed in fruits developed after self-pollination and the nature of the complex mechanism of self-incompatibility in Acianthera.