Uncovering the Neglected Floral Secretory Structures of Rhamnaceae and Their Functional and Systematic Significance.

Carimi Ribeiro,Cristina Marinho,Simone Teixeira

doi:10.3390/plants10040736

Carimi Ribeiro, Cristina Marinho + Show 1 more

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https://doi.org/10.3390/plants10040736

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Abstract

Rhamnaceae flowers are notably recognized by their fleshy nectary. Other types of floral secretory structures have been scarcely reported for this family. Thus, the objective of the present study was to update the occurrence of these structures in the family and to contribute to the knowledge of their morphology and systematic significance. To this end, we carried out an extensive bibliographic search on the secretory structures of the family and obtained data for 257 taxa. Additionally, we presented here novel data (surface, anatomy, and ultrastructure) for six species belonging to the main clades within Rhamnaceae. The family has a wide diversity of types of mucilage-secreting structures: epidermis, hypodermis, idioblasts, cavities, and ducts. Mucilage and phenolic idioblasts are widely distributed among the floral organs. Colleters are present in all sampled species, and these are the first reports of their occurrence in floral organs of Rhamnaceae. The information obtained about the structure, secreted content, and occurrence of the secretory structures of Rhamnaceae helped us to understand the assertive folk use of its species. The absence of mucilage and the presence of resin or mucilage cavities and ducts in some taxa may have intrafamily systematic significance.

Highlights

IntroductionDue to its easy visualization, this type of floral secretory structure has been the most studied in the group, both in terms of its functionality [3,4,5,6,7] and morphology [8,9]
Colleters are emergences found on the adaxial side of floral bracts (Colubrina glandulosa, Hovenia dulcis, and Rhamnidium elaeocarpum) and inflorescence bracts (Gouania latifolia, Gouania virgata, and Sarcomphalus joazeiro)
The present study updated the occurrence of these structures in the family and contributed to the knowledge of their morphology and systematic significance

Summary

Introduction

Due to its easy visualization, this type of floral secretory structure has been the most studied in the group, both in terms of its functionality [3,4,5,6,7] and morphology [8,9] Likewise, this family is recognized by the presence of epidermal cells, idioblasts, and cavities/ducts that secrete mucilage, found in its vegetative organs, mainly leaves [10,11,12,13,14,15,16,17,18,19,20,21,22]. These lesser-known structures had been reported only by Schirarend and Hoffmann [23], who explored the floral anatomy of 18 species of the genus Reynosia and in a study recently published by Gotelli et al [24], which describe and compare the structure of the osmophores in 11 species of the main clades of the family

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