Taxonomic considerations about the anatomical description of Gynecium Oxypetalum appendiculatum Mart. (Apocynaceae)

Abstract

The flowers of Apocynaceae are considered as the most complex among the angiosperms, due to the occurrence of synorganization culminated in the origin of a new floral structure, the gynostege, formed by the union of androceu and gynecium, which guarantees an optimization in the reproduction process. The gynostegium is widespread in the genera of the subfamily Asclepiadoideae, being cited as an artifact of taxonomic significance in the group. Oxypetalum R.Br. It is the largest neotropical genus of Asclepiadoideae and is included in Clado MOOG, which presenting difficulties regarding the taxonomic positioning of its species. Few studies have investigated the floral anatomy of Oxypetalum and these did not address the taxonomic significance of the anatomy of the gynostegium in resolving the positioning of individuals in the group. This work seeks to investigate the anatomy of the gynecium and the gynecium of Oxypetalum appendiculatum in order to contribute to the group's taxonomy. With this, we seek to show key anatomical parameters for the easy identification of gaps in that group. Buds and flowers at pre-anthesis, anthesis, and post-anthesis were collected to analyze histologically. Material was fixed in arnovsky’s solution and gradually dehydrated in an ethanol series. Samples were infiltrated, and embedded in hydroxyethyl methacrylate. Circa 5 µm cross and longitudinal sections were cut using a rotary microtome, stained with Toluidine Blue O. All the slides were analyzed with optical and stereo microscopes and images were captured with a photomicroscope or a trinocular photo stereomicroscope. Gynoecium comprises two carpels fused at style and style head, with free ovaries. The five receptive parts of stigma are located on the gynostegium, more precisely behind the translators. At a higher level, the stigma begins to divide, appearing bifid, towards the apex. The gynoecium of Oxypetalum appendiculatum is an extremely complex structure due to the synorganization that occurred between the corona, the anthers and the gynecium itself. The result of this union is the gynostegium, which provides morphoanatomical characters that assist in delimiting this taxon and other species of this genus.

Keywords

• asclepiadoideae
• bifid attachment
• anatomy
• taxonomy
• gynostegium.