Pollen development and orbicule and pollen grain morphology in species of Cephalanthus (Rubiaceae-Naucleeae) from the Americas

Abstract

This paper is the first embryological report on the genus Cephalanthus L. and contributes to future studies in other genera of the tribe Naucleeae. The development of the anther wall in Cephalanthus glabratus (Spreng.) K. Schum. corresponds to the dicot type and microsporogenesis is simultaneous. The young wall of the anther has four layers; epidermis, endothecium, one middle layer and the secretory tapetum. The tissue of the septum has idioblasts with crystalline sand. In the wall of the mature anther, only the endothecium and remnants of epidermal cells were preserved. The occurrence and morphology of orbicules were observed in the mature anthers of all three species of Cephalanthus with scanning electron microscopy. The orbicules have taxonomic value at species level, since these structures allow us to distinguish between the species analysed. The presence of a protruding oncus was observed for the first time in Cephalanthus in non-acetolysed pollen grains. According to our observations, this structure is not affected by the state of anther dehiscence in C. glabratus because the oncus is visible and prominent in the mature pollen grains in both indehiscent and dehiscent anthers.

Anther structure and pollen development in species of Rubiaceae and anatomical evidence of pathway to morphological dioecy

“…The persistence of the middle layers has shown variation between the anthers of the different types of flowers analysed. In PF and FSF these layers collapse early, as described for perfect flowers of other Rubiaceae (Dedecca 1957, Galati 1991, Hansson & El-Ghazaly 2000, Vinckier & Smets 2005, Magalhães Souza et al 2008, Romero et al 2017, Yue et al 2017. However, in the FPF of C. concolor, G. americana and R. calycina, the anther middle layers may persist even when the endothecium of the anther has already thickenen.…”

“…In Rubiaceae the anatomical descriptions of the stamens have been mainly focused on species with perfect flowers (Dedecca 1957, Galati 1991, Hansson & El-Ghazaly 2000, Vinckier & Smets 2005, Magalhães Souza et al 2008, Romero et al 2017, Yue et al 2017. The only known embryological study on imperfect flowers was conducted in Mussaenda pubescens (Li et al 2010).…”

“…These dispersal units can be used as a source of information for phylogenetic analysis (Dessein et al 2005) or analyzed in combination with molecular data (Gustafsson & Persson 2002). The orbicules (or Ubisch bodies) also represent a very interesting taxonomic feature in Rubiaceae because they vary in abundance, size, shape and ornamentation (Huysmans et al 1997, Vinckier et al 2000, Dessein et al 2005, Verellen et al 2007, Verstraete et al 2011, Romero et al 2017).…”

Colleters in Cephalanthus (Rubiaceae) and reevaluation of occurrence of corolline colleters in Angiosperms

“…Cephalanthus natalensis is the only species without corolla "glands" according to Ridsdale (1976) and Razafimandimbison & Bremer (2002). Razafimandimbison & Bremer (2002) and Romero et al (2017) mentioned that these "glands" correspond to colleters, but there are no morpho-anatomical descriptions or any histochemical evidence of them.…”

Iridoids and seco-iridoids from the leaves of Cephalanthus glabratus (Spreng.) K.Schum

“…The species is native to Brazil, Uruguay and Northern Argentina, where it grows near rivers and lakes and represents the vegetation closest to water also favoring the habitat for the herons nesting. In the literature, the works about this species mainly treat about its ecological and botanical aspects (Romero et al 2017(Romero et al , 2019Wolff Kettenhuber et al 2019). Indeed, only three works deal with its phytochemistry (Hnatyszyn et al 1976;Phillipson et al 1982;Marinho Jorge et al 2006), evidencing the presence of terpenoids, phenolics and tannins plus some specific alkaloids and ursolic acid.…”