Biologia floral e polinizadores de Hygrophila paraibana rizzini (Acanthaceae), espécie rara e endêmica de brejos de altitude do nordeste brasileiro

Abstract

In northeastern Brazil, the Brejos de Altitude (upland humid forests) represent peculiar ecosystems embedded within the Caatinga domain, exhibiting specific edaphoclimatic characteristics. These environments serve as true refuges of biodiversity and harbor a large number of endemic species, making them priority areas for conservation. Within this context lies Hygrophila paraibana Rizzini, a plant belonging to the Acanthaceae family, restricted to fragments of Brejo de Altitude in the state of Paraíba. Despite its ecological relevance, little is known about the floral biology of this species, as well as its reproductive strategies and pollinators. This study aimed to understand the reproductive mechanisms and ecological interactions of H. paraibana. Analyses of floral biology were carried out, along with field observations in natural populations to identify the behavior and frequency of floral visitors and determine potential pollinators. The flowers present a bilabiate corolla, two pairs of didynamous stamens, and a stigma longer than the anthers. These morphological features promote contact between visitors landing on the lower lobe of the corolla to access floral rewards, while reducing the likelihood of self-pollination. Among the observed visitors, the flower fly Toxomerus sp. demonstrated efficient visiting behavior, touching the reproductive structures and showing high effectiveness in pollen transfer, thus being considered the effective pollinator of H. paraibana. The species Trigona spinipes exhibited nectar-robbing behavior, perforating the corolla without contacting reproductive organs, and was therefore classified as a nectar robber. It is concluded that H. paraibana exhibits a myiophilous pollination syndrome, characterized by pollination mediated by flies. The results highlight the ecological importance of Diptera as pollinators, emphasize the relevance of understanding these interactions for the conservation of Brejos de Altitude, and contribute to future studies of the Acanthaceae family in Paraíba.