Description of a new species within the Satyrium longicauda (Orchidaceae) complex from South Africa, based on integrative taxonomy

Abstract

Although delimitations of plant species are traditionally based on the study of herbarium specimens, new species can also be identified using multiple lines of evidence (integrative taxonomy). An integrative approach was implemented to identify a new species of the orchid genus Satyrium from the Midlands area of KwaZulu-Natal, South Africa, described here as S. cernuum. This species shares an overall similar floral morphology with five other sympatric morphotypes within the S. longicauda complex reported from the type locality but can be diagnosed by a combination of vegetative and floral traits and flowering phenology. According to a published phylogeny based on DNA sequences, the new species forms a monophyletic clade that is nested within S. longicauda and is supported as sister to the other S. longicauda morphotype that is uniquely characterised by a single erect leaf. The new species differs from this morphotype by the orientation of its flowers which are obtuse (vs. right-angled) relative to the inflorescence stem, spreading (vs. spreading to recurved) sepals, relatively short (vs. long) spurs that lack nectar and by its production of elevated levels of diacetin, a fatty-acid derived compound. Other S. longicauda morphotypes differ in the number and position of their leaves and a later flowering period. In addition, the new species is exclusively pollinated diurnally by the oil-collecting bee species Rediviva neliana, rather than being pollinated nocturnally by settling moths and hawkmoths; it is thus reproductively isolated from sympatric morphotypes. The formal recognition of the new species, which is known from two adjacent populations in an area of occupancy ≤1 km2 makes it a matter of immediate conservation concern. An identification key to the morphotypes of the S. longicauda complex from KwaZulu-Natal, including the newly described species, is provided. This study shows the value of using integrative taxonomy in the South African flora for the recognition of recently diverged taxa.