Pollinator Visitation Within a Single Crown of the Rare Rainforest Tree Firmiana daweishanensis Is Associated With Floral Colour Change.

Floral colour change can signal floral state, but its role in rainforest canopy trees remains poorly understood. We investigated colour change and pollinator visitation in Firmiana daweishanensis, a Plant Species with Extremely Small Populations endemic to southeastern Yunnan, China. Using a 25-m scaffold, we observed 16 flowering branches on one adult tree for 128 branch-hours. We combined these observations with measurements of linalool emission, nectar accumulation, reproductive function, calyx reflectance and bee visual modelling. Six hymenopteran taxa visited the tree, with Megachile bees dominating visitation. Mixed models showed that yellow flowers received more visits and greater cumulative visitation time per flower-hour than red flowers within both sexes. Neither the omnibus sex tests nor the colour × sex interactions were significant. Branch-level floral abundance and colour composition were not significantly associated with visitation. This contrast was consistent with, but did not demonstrate, selection at a fine spatial scale; limited statistical power remained an alternative explanation. Yellow flowers showed higher linalool emission and stronger modelled green-receptor contrast against a green background. Nectar availability and reproductive function were generally greater during earlier floral stages. Neither pollinator-excluded nor artificially geitonogamously self-pollinated flowers produced fruit, whereas naturally exposed flowers showed 6.19% fruit set. These observations support a contribution of floral visitors to fruit set, but the absence of a hand-cross-pollinated control prevented a conclusive assessment of self-incompatibility. Because colour, age, scent, reward and reproductive state covaried, their individual contributions to visitation could not be distinguished. Floral colour change may therefore form part of a multimodal indicator of floral state, while any display function of retained red flowers remains hypothetical. This within-tree case study documents canopy visitation patterns whose generality requires replication across individuals and populations.