Ruellia blechum: A new case of cleistogamy in Acanthaceae

Cleistogamy is characterized by the presence of flowers that are permanently closed, yet they still produce fruits and seeds through autonomous self-pollination. Populations with cleistogamous flowers can also have flowers that open, called chasmogamous, which promote cross-pollination and genetic variability. Acanthaceae is among the families with the highest frequency of cleistogamy, observed mainly in Ruellia. This study aimed to assess cleistogamy in Ruellia blechum for the first time. In a population in Central Brazil, we analysed the production of cleistogamous and chasmogamous flowers, their fruiting, differences in flower bud size, self-pollination in cleistogamous flowers and visitors in chasmogamous flowers. Of the flower buds observed, 35.29% remained closed (cleistogamous flowers), with 31.25% of them forming fruit. In contrast, 60.24% of the flowers that opened (chasmogamous) developed fruit. The length of cleistogamous flowers was shorter than that of chasmogamous floral buds in pre-anthesis. On average, 24.45 pollen grains were self-deposited on the stigma of a cleistogamous flower. The chasmogamous flowers were visited mainly by small bees. This study is the first to confirm the presence of cleistogamous flowers in R. blechum. However, their co-occurrence with chasmogamous flowers suggests a fitness advantage for maintaining a mixed mating strategy.