Is biodiversity underestimated by classical herbarium-based taxonomy? A multi-disciplinary case study in Satyrium (Orchidaceae)

Abstract

Taxa relegated to synonymy with other superficially similar taxa based on herbarium-based taxonomy may be distinct species that are only 'rediscovered' on the collection of new, multi-disciplinary evidence. Here we investigate the case of Satyrium jacottetiae that has been included in the concept of S. membranaceum (Orchidaceae). The two taxa share similarities in some conspicuous traits, such as the dry and membranous floral bracts, light pink labellum and laceration of the petals, but a quantitative morphometric analysis based on 23 floral traits showed that the two taxa differentiate in ordination space. We found that the taxa can be distinguished by features of the rostellum (short and broad in S. jacottetiae and elongate and notched in S. membranaceum), which are not readily apparent from examination of herbarium specimens. A phylogenetic analysis of nuclear ribosomal DNA sequences further revealed that accessions of S. jacottetiae belong to a clade that contains two other Satyrium spp. but not S. membranaceum. The two taxa have largely non-overlapping distributions on slightly different soil types, but they also maintain their integrity in the few zones of overlap despite evidence indicating that both are primarily pollinated by nocturnal moths. Coexistence in these cases of sympatry appears to be facilitated by a sequential difference in flowering times. We conclude that S. jacottetiae and S. membranaceum are morphologically, phylogenetically, geographically and ecologically distinct and should therefore be recognized as separate species. This study highlights the importance of multi-disciplinary taxonomic effort to avoid under-assessment of biodiversity.