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The Melastomataceae family, the largest radiation of pollen flowers, has been reported to offer floral oils exclusively in the Olisbeoideae subfamily. However, species from other clades such as Macairea radula (Marcetieae, Melastomatoideae) exhibit staminal glands that secrete oil-like viscous substances whose chemical composition and function are still unknown. We used anatomical sections and histochemical tests to characterize these staminal glands and their exudate. We also used GC–MS to characterize the chemical composition of the oil from the flowers and the scopae of visiting oil bees (Centris aenea). The staminal glands consist of glandular emergences with a multiseriate stalk and a conspicuous multicellular secretory head. Histochemical tests revealed the presence of lipids and phenolic compounds inside the glandular head cells. Although histologically different from trichomes, these glands are morphologically similar to trichomatic elaiophores. GC–MS confirmed the non-volatile lipidic nature of the staminal gland secretion, which consists of a mix of medium to long chain alkanes and nutritious fatty acids. Therefore, M. radula staminal glands produce oils similar in composition to the oils produced as bee reward by other angiosperm flowers. Some of these compounds were also found in the oils extracted from visiting bee scopae, suggesting that the oils produced by the staminal glands can be collected by bees. In addition, or alternatively, these oils could promote better adhesion of pollen to the bee's body. Oil production by staminal glands of M. radula may attract oil-collecting bees more consistently, ultimately contributing to the plants’ reproductive success.

Due to deforestation and fragmentation of ecosystems, the management of bee populations targeting pollination services is increasingly urgent. Because urban environments are stressful, the dietary knowledge in such areas can help to cope with this issue in the near future. Using palynological analysis the floral resources used by Centris flavifrons, an important pollinator of crops and native plants was studied in an urban area. Byrsonima sericea type, Solanum paniculatum type, Cestrum type, and Myrcia type 1 together accounted for more than 93% of pollen grains foraged by females. It is noteworthy that this bee population depends on few plant species both for pollen and for oil. Furthermore, females showed flexibility to replace the primary pollen source in different breeding seasons, as well as one female could provision different cells in the same nest with different predominant pollen types. It is highlighted the importance of wastelands for keeping bee populations in urban areas.

Floral oils as reward to pollinators occur in eleven plant families and appeared at least 28 times in the evolutionary history of flowering plants. They are produced in epithelial or tricomatic glands and collected by oil bee visitors. The present paper focuses on floral-oil-producing species of Plantaginaceae, a Neotropical group namely Angelonia clade. This group comprises around 40 described species in the genera Angelonia, Basistemon, Monttea, Monopera and the oil-less Melosperma. We present a revision of all species of the Angelonia clade, their geographical distribution, resources offered to pollinators and records of flower visitors, especially oil-collecting bees. These plants rely only on oil-collecting species in the tribe Centridini and Tapinotaspidini for a successful pollination, being the interaction between both partners an especial case of bee/flower adaptation in Neotropical region. Some bee species depend only on the oil of Plantaginaceae flowers to survive, while others can collect on several floral oil sources. The pollinating bees explore the oil glands located in sacs using specialized hairs in the forelegs. With this study, we hope to inspire further research relating to this fascinating group of plants, in which most species are rare and occur in highly endangered habitats in South American open vegetation biomes. Os óleos florais como recompensa a polinizadores estão presentes em onze famílias e surgiram ao menos 28 vezes na história evolutiva das plantas floríferas. Estes são produzidos em glândulas tricomáticas ou epiteliais e coletados por abelhas coletoras de óleo. O presente trabalho foi focado nas espécies produtoras de óleo floral de Plantaginaceae, um grupo neotropical conhecido como clado Angelonia. Este grupo compreende cerca de 40 espécies nos gêneros Angelonia, Basistemon, Monttea, Monopera e Melosperma, que não produz óleo floral. Nós apresentamos uma revisão de todas as espécies no clado Angelonia, sua distribuição geográfica, recursos oferecidos e registros de visitantes florais, especialmente abelhas coletoras de óleo. Estas plantas dependem das abelhas coletoras de óleo das tribos Centridini e Tapinotaspidini para uma polinização bem-sucedida, sendo a interação entre ambos os parceiros um caso especial de adaptação abelha/planta na Região Neotropical. Algumas espécies dependem somente do óleo coletado em espécies do clado Angelonia, enquanto outras também podem coletar em várias fontes de óleos florais. Essas abelhas exploram as glândulas de óleo localizadas em bolsas utilizando pelos especializados nas pernas anteriores. Com o presente trabalho esperamos inspirar estudos futuros com este fascinante grupo de plantas, que são em sua maioria espécies raras e que ocorrem nos altamente ameaçados biomas de vegetação aberta da América do Sul.

A polinização, o sistema reprodutivo e a fenologia da floração de Byrsonima gardnerana A. Juss foram estudados em uma área de Caatinga situada no Parque Nacional do Catimbau, Agreste de Pernambuco. Byrsonima gardnerana é uma espécie arbustiva com flores hermafroditas e zigomorfas, que mudam de cor em decorrência da polinização. O recurso floral primário é o óleo. O padrão de floração é anual, durando 4-5 meses, ao longo da estação seca. A espécie é auto-incompatível, apresenta alta viabilidade polínica e elevada razão pólen/óvulo. Foram observadas 11 espécies de abelhas visitando as flores de B. gardnerana, nove delas atuando como polinizadoras (sete espécies de Centris) e duas como pilhadoras de pólen. As espécies de Centris foram as mais freqüentes e efetivas, coletando óleo e pólen, neste caso vibrando as anteras, sempre contatando as estruturas reprodutivas das flores. Flores de B. gardnerana constituem, portanto, importante fonte de alimento para as abelhas especializadas nativas, cuja necessidade dos óleos florais na composição da dieta de suas larvas garante constantes visitas. The pollination ecology, the reproductive system and the flowering phenology of Byrsonima gardnerana A. Juss were studied in a Caatinga area of the Parque Nacional do Catimbau, Pernambuco state, Brazil. The species is a shrub with hermaphrodite and zygomorphic flowers, which change color after pollination, with oil as primary floral resource. Flowering pattern is annual, lasting 4-5 months, occurring along the dry season. The species is self-incompatible, has elevated pollen viability and high pollen/ovule ratio. Eleven species of bees were observed visiting the flowers of B. gardnerana, nine of them behaving as pollinators (seven Centris spp.) and two as pollen thieves. Bees of the genus Centris were the most frequent and effective floral visitors, collecting oil and also pollen, in this case vibrating the anthers, always contacting the reproductive structures of the flowers. The flowers of B. gardnerana are, therefore, an important resource to specialized native bees that feed their larvae with floral oils, hence guarantying frequent visits to the flowers.

Notas sobre fontes de óleos florais do gênero Caenonomada (Hymenoptera, Apidae, Tapinotaspidini). Pela primeira vez é reportado a coleta de óleo por Caenonomada em Plantaginaceae. Fêmeas de Caenonomada unicalcarata foram observadas coletando óleo em flores de Angelonia cornigera, e fêmeas e machos de Caenonomada bruneri e Caenonomada aff. unicalcarata em flores de Angelonia e Monopera (Plantaginaceae). O registro de Caenonomada em Plantaginaceae sugere uma condição mais primitiva para o uso de glândulas tricomáticas de óleo na tribo Tapinotaspidini. Notes on oil sources for the bee genus Caenonomada (Hymenoptera, Apidae, Tapinotaspidini). It is reported for the first time oil collecting by bees of the genus Caenonomada on flowers of Plantaginaceae. Females of Caenonomada unicalcarata were observed collecting oil on flowers of Angelonia cornigera, and males and females of Caenonomada bruneri and C. aff. unicalcarata were observed on flowers of Angelonia and Monopera (Plantaginaceae). The record of Caenonomada on Plantaginaceae suggests the use of trichomatic oil glands as a primitive condition in the tribe Tapinotaspidini.