Explorando a macroevolução de Cryptangieae (Cyperaceae): citogenética e biologia reprodutiva de uma tribo neotropical

Abstract

Cyperaceae showcases complex inflorescences and diversity of sexual systems, making it an interesting study subject for evolutionary questions. Cryptangieae, one of its tribes, comprises seven genera (Cephalocarpus, Cryptangium, Didymiandrum, Exochogyne, Krenakia, Koyamaea, Lagenocarpus) and exhibits unique characteristics such as reddish stigmas, predominance of unisexual spikelets, and diverse inflorescence morphology. With the aim of an integrative approach, this study presents analyses of cytogenetics, palynology, floral anatomy, and reproductive biology to better understand the evolution of Cyperaceae, with emphasis on Cryptangieae. Through comparative phylogenetic methods, it was found that in Cyperaceae there was a correlation between the increase in the number of spikelets and the presence of branching, which may benefit pollen dispersal and capture. Unisexual flowers are likely a plesiomorphic characteristic for the family, while bisexual ones are derived. In Cryptangieae, major cladogenesis events were possibly marked by ascending dysploidy, with evidence of holocentricity. Species of Cryptangium, Krenakia, and Lagenocarpus have 2n = 32, 42, and 34, respectively. The tribe is palynologically diverse, with an evolutionary trend towards larger pollen size and a reduction in the number of grains produced per anther. In Cryptangieae, the presence of glandular trichomes on the pistils provides evidence for floral visitor attraction. These visitors are capable of carrying pollen grains, but controlled pollination experiments are still needed to confirm ambophily in the tribe. Finally, from a dated phylogenetic tree, it was detected that the tribe diverged approximately 25 Ma (Oligocene), with evolutionary radiation from 2.6 Ma (Pleistocene). Overall, genera with Amazonian distribution diverged earlier than those with distribution in the Cerrado. In Cryptangieae, it is likely that the increase in the number of female flowers occurred preferentially in tufted species. This situation may benefit pollen capture and seed production, mainly in Krenakia and Cryptangium. On the other hand, in Lagenocarpus, dimorphic inflorescences were considered key innovations, as the clade of campos rupestres is potentially more diverse than the Amazonian group. Furthermore, the emergence of this characteristic coincided with the separation of the mentioned groups, suggesting a significant role in the genus and tribe's diversity explosion as a whole. Different paleoenvironmental conditions, especially climatic and landscape fluctuations between the Miocene and Pleistocene, may have influenced the selection of different reproductive strategies in species of Krenakia and Lagenocarpus occurring in campos rupestres.