Embryology in helosis cayennensis (Balanophoraceae) : structure of female flowers, fruit, endosperm and embryo
Fecha
2019Autor
González, Ana María
Sato, Héctor Arnaldo
Marazzi, Brigitte
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Helosis cayennensis (Balanophoraceae s.str.) is a holoparasite characterised by aberrant
vegetative bodies and tiny, reduced unisexual flowers. Here, we analysed the development of female
flowers to elucidate their morpho-anatomy and the historical controversy on embryo sac formation.
We also studied the developmental origin of inflorescences and the ontogeny of fruits, embryo and
endosperm and discussed in a phylogenetic framework. Inflorescences were analysed by optical,
fluorescence and scanning electron microscopy. Inflorescences of H. cayennensis arise endogenously.
Female flowers lack perianth organs, thus only consist of the ovary, two styles and stigmata. Ovules
are undifferentiated; two megaspore mother cells develop inside a nucellar complex. The female
gametophyte, named Helosis-type, is a bisporic four-celled embryo sac, provided with a typical egg
apparatus and a uni-nucleated central cell. Fertilization was not observed, yet a few-celled embryo
and cellular endosperm developed. In sum, results confirm that, among Santalales holoparasites,
Helosis is intermediate in the reduction series of its floral organs. Although perianth absence best
supports the Balanophoraceae s.str. clade, our literature survey on female flower developmental data
across Balanophoraceae s.l. highlights the many gaps that need to be filled to really understand these
features in the light of new phylogenetic relationships.
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