Geraniales flowers revisited: evolutionary trends in floral nectaries

Abstract

Floral morphology of the Geraniales shows a high degree of similarity, despite the variation in overall floral appearance and nectary morphology. A hypothesis on the transformation of the nectaries within the Geraniales is presented.

The relationship between nectaries and floral architecture: a case study in Geraniaceae and Hypseocharitaceae

“…Most of the species in this study across Geranium, Erodium and Monsonia show different levels of complexity of floral architecture, synorganization and compartmentalization, but Pelargonium represents an entirely different type of floral organization. In the zygomorphic flowers of Pelargonium, four of the five nectary glands, present in the other genera, have been lost (Jeiter et al, 2017). The intercalary growth of the receptacle here also includes the bases of the sepals.…”

“…In Pelargonium, the number of fertile stamens ranges from two to seven while in Hypseocharis tridentata only five fertile stamens are present. Considering the common number of ten stamens in Geraniaceae and other genera of the Geraniales (Jeiter et al, 2017), a hypothetical common ancestor with a pentacyclic flower seems to be more likely than one with a tetracyclic flower with one whorl of five stamens as proposed by Ronse De Craene and Bull-Hereñu (2016).…”

“…The present study of nectary ontogeny in Geraniaceae and Hypseocharitaceae shows that the overall nectary development and floral organization is similar across the taxa studied. They are classified as axial (receptacular) nectaries (Smets, 1988;Smets and Cresens, 1988;Jeiter et al, 2017). Apart from differences in shape and size, major differences occur in the timing of the development of the nectarostomata, through which nectar is exudated (early in Hypseocharis, Geranium and Pelargonium, and late in Erodium and Monsonia).…”

“…Several authors investigated the ontogeny, anatomy and morphology of the floral nectaries in the Geraniaceae and related families and genera (e.g. Link, 1989Link, , 1994Vogel, 1998; Ronse Decraene and Smets, 1999;Jeiter et al, 2017). Flowers of species from both families are shown in Fig.…”

“…All five genera of the Geraniaceae and the one of Hypseocharitaceae have flowers that reward nectar. The position of the nectaries at the base of the antesepalous filaments between the bases of the neighbouring petals is conserved within both families (Jeiter et al, 2017). The only apparent exception is found in Pelargonium, where the nectar is hidden in a spur-like cavity on the adaxial side of the flower.…”