Nectary structure is not related to pollination system in Trichocereeae cactus from Northwest Argentina

Abstract

Fl oral nectaries are essential for plant reproduction but little is known about the relationship between these secretory structures and pollination system in cacti. To test phenotypic patterns in nectaries associated with pollination syndromes and/or with its pollinators, we selected from evolutionarily related genera Cleistocactus, Denmoza, and Echinopsis, a set of species with bird-pollinated fl owers and fl oral traits that may fi t with ornithophily or with sphingophily, and other set of sphingophilous species with moths as effective pollinator. Observations were made under light microscope and scanning and transmission electron microscopes. Nectaries are located at the base of the fi laments welded to the tube, forming a chamber. Th e nectary consists of the epidermis with distinctive features in each genus, a secretory parenchyma which may be vascularized and a non-secretory vascularized parenchyma. Anatomical variants observed in nectaries of different species are not consistent with the fl oral pollination syndromes neither with groups of pollinators. The basic structure of the nectar chamber is relatively conserved, a fact that may be explained by phylogenetic conservatism among the genera investigated. Our results revalue the role of anatomical traits for the systematics of Cactaceae.

Synchrotron micro-computed tomography unveils the three-dimensional structure and origin of staminodes in the Plains Prickly Pear Cactus Opuntia polyacantha Haw. (Cactaceae)

“…In the Cactaceae, the stamens are initiated in centrifugal progression from a primary ring in the floral cup (Ross 1982) as demonstrated in the conspicuous androecia of Disocactus (Buxbaum 1953) and Schlumbergera truncata (Apolônio 2022). Recent developmental studies in the family report non-vascularized staminodes originating in the upper portion of the nectar chamber of Denmoza rhodacantha (González et al 2021), a major difference from the rather vascularized staminodes and tepals seen in O. polyacantha in this study.…”

“…Thus, the conductive tissue extends to the subnectariferous parenchyma vascularizing every stamen filament in the androecium as well as the adjacent tissues (nectary, floral tube, and androecium), merging in a common vascular network. Conversely, the vasculature in the floral nectary of D. rhodacantha exhibits traces of branching xylem and phloem ducts infiltrating the nectariferous parenchyma (González et al 2021). These contradictory data suggest that additional investigations in other groups of the Cactaceae are required to fully understand the organization of the vascular system and the presence of a common or different points of origin for these structures.…”