Accepted Article This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/nph.16137 This article is protected by copyright. All rights reserved. PROF. TIA-LYNN ASHMAN (Orcid ID : 0000-0002-9884-5954) Article type : Viewpoint Gazing into the anthosphere: Considering how microbes influence floral evolution Summary The flower is the hallmark of angiosperms and its evolution is key to their diversification. As knowledge of ecological interactions between flowers and their microbial communities (the anthosphere) expands, it becomes increasingly important to consider the evolutionary impacts of these associations and their potential eco-evolutionary dynamics. In this viewpoint we synthesize current knowledge of the anthosphere within a multilevel selection framework and illustrate the potential for the extended floral phenotype (the phenotype expressed from the genes of the plant and its associated flower) to evolve. We argue that flower microbes are an important, but understudied, axis of variation that shape floral trait evolution and angiosperm reproductive ecology. We highlight knowledge gaps and discuss approaches that are critical for gaining a deeper understanding of the role microbes play in mediating plant reproduction, ecology, and evolution. Introduction Flowers function for sexual reproduction and seed and fruit development, and it is acknowledged that their interactions with pollinators and seed dispersers lead to the diversification of angiosperms (Magallón et al., 2018). As a complex, nutrient-rich structure, the flower is also a unique environment for microbial communities: it consists of multiple niches differing in morphology, chemical composition and longevity. The function of these niches changes over the course of the flower’s life (Junker et al., 2011; Aleklett et al., 2014; Wei & Ashman, 2018).