Development of carpels and ovules in Dialypetalanthus fuscescens Kuhlm. (Rubiaceae): an enigmatic taxon

Abstract

Dialypetalanthus is a monospecifi c genus that occurs in the Amazon Basin of Brazil, Bolivia and Peru and occupies a controversial position among the Rubiaceae. We continue this taxonomic discussion with the overall aim of clarifying the systematic position of D. fuscescens within the Rubiaceae. To accomplish this, we analyzed the ontogeny of its gynoecium, in particular the fl oral meristem, as well as the development of the carpels and cauline placentation. Gynosporogenesis and the diff erentiation of the carpellary septa and ovules were also described. Dialypetalanthus fuscescens was classifi ed according to evolutionary diagrams found in the literature. Th e following characteristics were observed in D. fuscescens: 1) permanence of the fl oral meristem in the central basal part of the early fl ower bud; 2) dual origin of carpellary septum; 3) trizonate ovular primordia with only one fertile gynospore per ovule; and 4) cellular proliferation in the chalazal region. Embryological results confi rm the classifi cation of D. fuscescens in the subfamily Ixoroideae. Th ese results are distinct from any others previously proposed in the evolutionary diagram. Th erefore, we conclude that this study has presented evidence strongly suggesting that Dialypetalanthus possesses new morphological-type of ovule we refer to as the Dialypetalanthus-type.

Floral ontogeny links Dialypetalanthus (Condamineeae) with the floral developmental morphology of other Rubiaceae

“…Only after the appearance of most stamens, the development of the gynoecium starts, similar as in other Rubiaceae (De Block and Vrijdaghs 2013;Vrijdaghs et al 2020), though without gynoecial nectary (Fig. 3C; Figueiredo et al 2017). Perhaps, investing in polyandry instead of a nectary gives an ecological advantage to Dialypetalanthus, but this is a subject for another study.…”

“…The ovary develops into a septicidal capsule with numerous winged seeds (e.g. Piesschaert et al 1997;Figueiredo et al 2017), features that are reminiscent of several rubiaceous genera, such as Mitragyna Korth. and other Naucleeae.…”

“…Piesschaert et al (1997) provided a study, only based on herbarium material, of the floral ontogeny of Dialypetalanthus. Figueiredo et al (2017) studied, using light microscopical observations, the development of the gynoecium in Dialypetalanthus. In this paper, based on light and scanning electronic microscopy, we present the results of a complete floral developmental study of Dialypetalanthus, including perianth and androecium.…”

An assessment of Coutaportla (Chiococceae, Rubiaceae) with the description of a new species from Mexico

“…apical in Vanguerieae and basal in Psychotrieae. However, some anatomical and development studies have shown that placentation can also be extremely variable in Rubiaceae (Svoma 1991;Figueiredo et al 2013Figueiredo et al , 2017. According to Ronse Decraene and Smets (2000), in Rubiaceae, the basal, central, or apical placentation are the result of differential degrees of development among the basal placental portion of the ovary and the apical portion of the style.…”