Format: ORAL

Cristina R. Marinho1, Llus Garca-Mir1, Luca del Castillo1, Elisa Romn1, Magui Olangua2, Olga Fernndez-Palacios2, Rosa Febles2, Yannick M. Staedler3, Jrg Schnenberger3, Javier Fuertes-Aguilar1

1 Real Jardín Botánico de Madrid (RJB – CSIC), Spain 2 Jardín Botánico Canario Viera y Clavijo (JBCVyC – UA CSIC), Spain 3 Department of Botany and Biodiversity Research, University of Vienna, Austria

The presence of floral nectaries (FN) composed of a carpet of multicellular secretory trichomes, is one of the most conspicuous features of Malvaceae. Although their location within the flowers is virtually constant in the Malvoideae subfamily, they display considerable morphological differences associated with specific pollination syndromes. Here, we aimed at understanding the evolution of the anatomy underlying the pollinator-mediated nectar secretion comparing the FN structure and development between three phylogenetically-related Malva species pollinated by insects (Malva wigandii, Malva canariensis) or birds (Navaea phoenicea). Buds and flowers were collected along seven developmental stages, from which FNs were dissected and processed for optical microscopy, SEM and CT-scan. Morphological parameters were digitally measured using ImageJ and analyzed with RStudio suite. We found changes in growth and differentiation patterns, anatomy, and starch metabolism relevant to nectar secretion. 1) Trichome inception developed synchronically among the five sepals in all species, but monocentrically in M. canariensis and M. wigandii, and polycentrically in N. phoenicea. 2) N. phoenicea FN takes longer to develop than other species, which may be related to its greater structural complexity. As a result, bird-pollinated N. phoenicea FN are much larger and show a nectariferous parenchyma that is more compact, thicker, and with abundant phloem vascularization. On the contrary, entomophilous species show smaller nectaries, with a parenchyma with intercellular spaces and few or no phloem terminations. 3) Trichomes have a similar shape, but they are shorter and tightly packed in ornitophilous N. phoenicea, which also accumulated more starch in the parenchyma over time than the other species. This study provides evidence for the intimate relationship between FN morphology and nectar production, showcasing the pivotal role of FN size and structure in determining nectar output across distinct pollination strategies.