Pollen morphology of the genus Euonymus (Celastraceae)

Abstract

Pollen of 62 species from the genus Euonymus (Celastraceae) were studied using light (LM), confocal laser scanning (CLSM) and scanning electron (SEM) microscopes. This is approximately half of the species composition of the taxon. The genus, as a whole family, is quite homogeneous by palynomorphological characteristics and represented by 3-colporate pollen type. On the other hand, some species and (or) group of species could be segregated considering the details of structure (aperture structures, exine ornamentation). We have found 3-colporate pollen in all investigated taxa and 19 species also have 2- and/or 4-6-deviated grains with different colpi arrangement. Their structure has been studied in more detail with a CLSM 3-dimentional reconstruction. Grains are isopolar, ellipsoidal or spheroidal medium sized, from 17 to 41 µm in diameter. Colpi are long, spired at the ends. Endoaperture (ora) range from poorly-defined, rounded or slightly elongared along the colpus up to well-defined, with sharp edges, elliptical and elongared along the equator. LM-observing shows H-shaped aperture; CLSM data demonstrate that they are constructed from ora bridge and exine thinning on both sides of parallel colpus. The exine is tectate, columellate, with well-defined columella layer. Exine thickness is from 1.5 to 5.1 µm. The ornamentation varies from reticulate to microperforate. The species groups divided according to their palynomorphological characteristics generally do not coincide with the genus subdivision onto subgenera and sections. The taxonomic significance of various palynological characteristics is discussed.