Satyrium liltvedianum: A newly discovered orchid species from the Kogelberg Mountains of the Cape Floristic Region (South Africa)

Abstract

Individuals of plant populations with traits which are inconsistent with any existing species description may represent intraspecific variants, products of hybridisation, or a novel species. To distinguish among these possibilities for a population of unusual Satyrium individuals from the Kogelberg Mountains in the Cape Floristic Region (CFR), morphological traits and floral scent were documented, and phylogenetic analyses implemented. Plants from the Kogelberg population were characterised by long-spurred white flowers and a bifid rostellum. Floral scent was dominated by the common floral monoterpene volatile β-linalool. Although these traits characterise several southern African members of the genus, DNA sequences from the nuclear and plastid genomes of an accession from the Kogelberg population were highly distinct from other Satyrium species. The Kogelberg accession occupied an isolated phylogenetic position within the ‘Satyrium clade’ and was not sister to any other species with similar traits. There was weak support for membership of a clade of species with which plants from the Kogelberg population share the possession of lateral sepals that project at a perpendicular angle to the median sepal, and cover the side of the labellum, and which also produce β-linalool as dominant scent compound. Given the congruence of phylogenetic relationships inferred from plastid and nuclear DNA sequences respectively, a hybrid status of the Kogelberg population was rejected. Based on these results, the new species, Satyrium liltvedianum, which is uniquely characterised by the size, shape and orientation of sepals and lateral petals, is described in this study. Other Satyrium species with similar floral traits are pollinated by crepuscular moths, which therefore can also be inferred for the new species. A dichotomous key to the white-flowered, long-spurred Satyrium species of South Africa is provided. The restricted distribution range, a typical phenomenon for many CFR plant species, in combination with the isolated phylogenetic position, suggests that S. liltvedianum represents a palaeoendemic species.