Protection and attraction: bracts and secretory structures in reduced inflorescences of Malpighiales

• We analyzed the ontogeny of glands and bracts of Malpighiales inflorescences.
• We studied the strategies related to the presence of whorls and types of glands.
• Bracts present both protection and attraction functions.
• Protection and nuptial secretory structures produce different chemical exsudates.
• Secretory structures and bracts are related to the evolutionary flower variation.

Flower protection and attraction of pollinators are mainly associated with the secretory structures. The flower-pollinator relationship corroborates these functions and is an essential link in the interpretation of different floral morphologies, such as the pseudanthia occurring in Euphorbiaceae and Peraceae, two near families in Malpighiales with several bracts and nuptial glands. Therefore, the aim of this study was to analyze the ontogeny and structure of glands and bracts present in unique, reduced inflorescences of Malpighiales, present exclusively in Euphorbiaceae and Peraceae, as well as the relationship of these structures with the floral morphology of the species. Dalechampia (Acalyphoideae), Euphorbia (Euphorbioideae), and Pera (Peraceae) pseudanthia were compared to Joannesia (Crotonoideae) flowers with regards to the strategies related to the presence of whorls and types of glands. Bracts and bracteoles have similar anatomical characteristics and compose the involucre and involucel of the pseudanthia. Some of these structures have a protection function, and others are used to attract pollinators as they are colorful and modified in glands. Colleters are found in early stages of development in Dalechampia and Euphorbia, and secretory idioblasts and laticifers occur in several stages of Pera and Joannesia, secreting exudates composed of mucilage, proteins, fatty acids and phenolic compounds, which act as protection. The resin gland of Dalechampia and nectaries of Euphorbia are derived from the involucral bracts, what is not observed in the nectaries of Joannesia. In this species, osmophores are present in the petals (first described here for the family) and act as nuptial glands. Secretory structures and different levels of bracts are related to morphological variation and the evolutionary history of the group and are important for the protection of fertile organs, pollination and species perpetuation.