Abstract Background: Plants and bees have coevolved throughout geological time, establishing a mutualistic relationship that results in feeding/resource obtention by bees and the reproductive success of angiosperms. Questions and Hypotheses: What is the floristic composition of the vegetation visited by bees in the Caatinga? How are pollen grains from Caatinga bee plant species characterized? Do pollen grains of bee plant species present characters that could be associated with the pollination process? Studied species: We studied the pollen grains of 45 bee plant species belonging to 41 genera and 23 angiosperm families. Among the studied species, 37 % are endemic to Brazil, and eight species are endemic to the Caatinga biome. Study site and dates: Apiary within the Caatinga biome, in the State of Bahia, Brazil. Climate warm semiarid. Fieldwork was carried out between August 2016 and June 2017. Methods: Plants in bloom and being visited by Apis mellifera were collected during biweekly field expeditions, herborized, identified, and deposited at the HUNEB herbarium. Pollen grains were acetolyzed, characterized, and microphotographed under light microscopy. Results: Forty-five bee plants were collected and classified according to field observations and specialized literature. Pollen morphology was variable, and nine species had their pollen morphology described for the first time. The apertures of the studied pollen grains were mainly tricolporate (44 %), pantoporate (15 %), and inaperturate (13 %), and exine ornamentation was mainly (micro)reticulate (46 %) and (micro)echinate (33 %). Conclusions: Our results suggest that bee plants present a set of palynological characters that may favor entomophily.

Resumen: Antecedentes: Plantas y abejas coevolucionaron, resultando en la alimentación/obtención de recursos por parte de las abejas y el éxito reproductivo de las angiospermas. Preguntas: ¿Cuál es la composición florística de la flora apícola en la Caatinga? ¿Cómo se caracterizan los granos de polen de las especies apícolas? ¿Los granos de polen de la flora apícola presentan características que facilitan la polinización? Especies de estudio: Se estudiaron los granos de polen de 45 especies apícolas vegetales pertenecientes a 41 géneros y 23 familias de fanerógamas. Entre las especies colectadas, el 37 % son endémicas de Brasil, con ocho especies exclusivas de la Caatinga. Sitio y años de estudio: Apiario en la Caatinga, Bahía, Brasil. Clima cálido semiárido. Colectas realizadas entre agosto de 2016 y junio de 2017. Métodos: Fueron colectadas las especies botánicas en floración que estaban siendo visitadas por las abejas Apis mellifera, posteriormente herborizadas, identificadas y adicionadas en la colección HUNEB. Los granos de polen fueron sometidos a acetólisis, caracterizados y fotomicrografados bajo microscopía óptica. Resultados: Se colectaron y clasificaron 45 plantas apícolas de acuerdo con observaciones de campo y literatura especializada. La morfología del polen fue bastante variada, con predominio del tipo tricolporado (44 %), pantoporado (15 %), inaperturado (13 %) y variación de la escultura exina, con predominio de polen (micro)reticulado (46 %) y (micro)equinado (33 %). Nueve especies fueron descritas palinológicamente por primera vez. Conclusiones: Nuestros resultados sugieren que existen características en la morfología de los granos de polen de las plantas apícolas que favorecen la polinización.

ABSTRACT Papilionoideae is the most diverse subfamily of Leguminosae, representing approximately 39 % of its species. Although it is particularly species rich and diverse in the Caatinga, the main phytophysiognomy of the semiarid Northeast Region of Brazil, little is known about the pollen morphology of the species that occur there. This study analyzes and describes the pollen morphology of the 27 species of Papilionoideae endemic to the Caatinga. Pollen grains were acetolyzed, mounted on permanent slides, measured, described and photomicrographed using light and scanning electron microscopy (LM and SEM, respectively). The main variable morphological features were pollen grain size, shape, amb, apertural type and exine ornamentation under LM (microreticulate, reticulate, psilate or finely scabrate) and SEM (microreticulate, reticulate, rugulate, granulate, fossulate and perforate). High intergeneric morphological heterogeneity was observed while morphological variation within each genus was subtle. Nonetheless, size, endoaperture shape, fastigium presence/absence and exine ornamentation were found to be important characteristics for the identification of some species.