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

Valeria V González,María S Ferrucci,Pablo Gorostiague,Pablo Ortega-Baes,Beatriz G Galati

doi:10.1590/0001-3765202120201401

Abstract

Floral 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 flowers and floral traits that may fit 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 filaments welded to the tube, forming a chamber. The 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 floral 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.

Highlights

The great diversity of floral phenotypes present in angiosperms has been traditionally linked to the specialization onto different groups of pollinators based on the concept of pollination syndromes (Faegri & Van der Pijl 1979, Fenster et al 2004)
This study aimed to explore the relationships between floral nectary structure and floral phenotypic specialization in bird-pollinated flowers of Trichocereeae species from northwest Argentina
Echinopsis albispinosa, E. ancistrophora, E. atacamensis, E. leucantha, E. schickendantzii and E. terschekii flowers exhibit sphingophilous specialization; they are funnelshaped with green floral tubes and white tepals (Figure 1e-j)

Summary

Introduction

The great diversity of floral phenotypes present in angiosperms has been traditionally linked to the specialization onto different groups of pollinators based on the concept of pollination syndromes (Faegri & Van der Pijl 1979, Fenster et al 2004). Current evidence indicates that even though cacti may exhibit phenotypic specialization, most pollination systems are generalist (Fleming et al 2001, De Viana et al 2001, Schlumpberger & Badano 2005, OrtegaBaes et al 2011, Alonso-Pedano & OrtegaBaes 2012, Eggli & Giorgetta 2015, Gorostiague & Ortega-Baes 2016, 2017), phenomenon that could be interpreted as only variations and not strictly functional adaptations Their flowers can be visited by a broad spectrum of animals, including unexpected types given their floral traits (Waser et al 1996).

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