Male Pomegranate (Punica granatum L.) Flowers Are Associated with Resource Limitation and Lack Female Reproductive Function

Sexual system plasticity strongly shapes plant reproductive fitness. However, empirical studies on andromonoecy have mostly focused on wild species, leaving gaps in our knowledge regarding cultivated fruit trees. In this study, we aimed to investigate the sexual system characteristics and adaptive responses to resource conditions of pomegranate (Punica granatum L.) in Kashi, Xinjiang, China. We assessed floral morphology and biomass, conducted resource manipulation treatments, pollen viability assays, and controlled pollination experiments, and observed pollinators. Our results indicated functional andromonoecy in pomegranate, in which male flowers originate from pistil degeneration, potentially in response to resource limitations within inflorescences. Hermaphroditic flowers showed advantages in morphology, biomass, floral rewards, and pollinator visitation. Male flowers could not produce fruits as maternal parents but generated viable pollen capable of siring progeny. However, they secreted less nectar and received significantly fewer pollinator visits than hermaphroditic flowers. These findings are consistent with the optimal resource reallocation hypothesis for maintaining andromonoecy, suggesting that male flowers may constitute a resource-saving strategy. Whether the male-flower proportion can serve as a reliable indicator of plant resource status requires further validation.