Petal epidermal cell shape has been shown to affect pollination success in flowering plants. Conical epidermal cells may increase grip for insect pollinators and enhance flower colouration compared to non-conical cells. Nicotiana (Solanaceae) presents a diverse range of petal cell shapes. Interestingly, sister species in at least two phylogenetically distinct clades of the genus have contrasting petal epidermal cell shapes (conical vs. non-conical). This project aims to further understand character evolution of petal cell shape in Nicotiana and its implications in pollination systems, combining tools of molecular biology, morphology and pollinator behaviour experiments. First, using a candidate gene approach, I explore in parallel the molecular mechanisms involved in petal cell shape differentiation of sister species with contrasting cell shape N. cordifolia and N. solanifolia (Section Paniculatae) and N. bonariensis and N. forgetiana (Section Alatae). Subgroup 9 R2R3 MYB transcription factors are potentially responsible for the molecular control of petal cell shape. Differential expression of subgroup 9 R2R3 MYBs in petals of the sister species, rather than sequence differences in these genes, might be explaining the contrasting cell morphologies. Next, I develop an Agrobacterium tumefaciens mediated transformation protocol for the non-model species N. forgetiana, a methodological advance crucial for further exploration of the molecular mechanisms and functional implications of petal cell shape. Lastly, I explore how petal colour and petal cell shape interact in the perception of flowers by model pollinator Bombus terrestris using biomimetic artificial flowers. Pollinator behaviour experiments indicate that the bumblebees can discriminate flowers with conical from flowers with non-conical surfaces, on a red and on a white background, using visual cues alone as well as tactile cues alone. This investigation improves our understanding of the molecular mechanisms involved in petal epidermal cell morphogenesis and of the functional implications of petal cell shape in the interaction flower-pollinator in Nicotiana.