To date, there is little evidence that phylogenetic diversity has contributed to nature conservation. Here, we discuss the scientific justification of using phylogenetic diversity in conservation and the reasons for its neglect. We show that, apart from valuing the rarity and richness aspect, commonly quoted justifications based on the usage of phylogenetic diversity as a proxy for functional diversity or evolutionary potential are still based on uncertainties. We discuss how a missing guideline through the variety of phylogenetic diversity metrics and their relevance for conservation might be responsible for the hesitation to include phylogenetic diversity in conservation practice. We outline research routes that can help to ease uncertainties and bridge gaps between research and conservation with respect to phylogenetic diversity. A promising but yet ambiguous additional biodiversity component for conservation More than two decades ago, Richard Vane-Wright et al. However, despite the increasing number of studies, the scientific proof of the added value of phylogenetic diversity for nature conservation remains weak. We believe that this is one of the main reasons why phylogenetic diversity is largely neglected in conservation practice In addition to the more general concept of conserving all components of biodiversity because of their intrinsic values, we identified four main conservation approaches that are commonly proposed as central justifications for the conservation of phylogenetic diversity: (i) the rarity aspect; (ii) the richness aspect; (iii) phylogenetic diversity as a proxy for functional diversity; and (iv) phylogenetic diversity as a proxy for evolutionary potential. Along these lines, we emphasize that a sound conceptual justification for the added value of phylogenetic diversity is often missing. We finally highlight desirable research avenues to increase our knowledge of the role of phylogenetic diversity and of how it could potentially improve conservation in the future. Phylogenetic diversity as an intrinsic biodiversity component One general agreement is to conserve all components of biodiversit
