Post-seminal development and morphoanatomy of vegetative and reproductive organs in Stevia rebaudiana (Bert.) Bertoni (Asteraceae)

Abstract Stevia rebaudiana belongs to the Asteraceae family with high economic and medicinal potential. This article describes and illustrates morphological and histological aspects of leaves and reproductive organs, and the germination process, to provide detailed information on this species and to contribute to taxonomic, phylogenetic and pharmacobotanical projects. The fruit is a cypsela, small, simple, dry, indehiscent, monospermic, light or dark colored, with aristate pappus, and the seed presents a spatulate axile embryo. Germination is phaneroepigeal with a pivotal root system and many absorbing root hairs. The leaves are simple, elliptical to obovate, with two types of trichomes (glandular and tector), with a short petiole, exhibiting an opposite decussate phyllotaxy. Our results showed 37.5% germination after 12 days, only in the dark cypsela, the light colored being considered unviable. The inflorescence is paniculate and the florets are grouped in capitula with isomorphic ends, monoclinous (bisexual), dichlamydeous, heterochlamydeous, pentamerous calyx and corolla, gamossepalous and gamopetalous. The androecium is gamostemone comprised of five stamens with free filaments, isodynamous and epipetalous stamens, synandrous and rimose anthers. The flower presents an inferior ovary, bicarpelar, unilocular and ovules with a basal placentation. The pollen grains are small, isopolar, radial symmetry, tricolporate, with echinate ornamentation.