New insights into variation, evolution and taxonomy of fairy lanterns (Thismia, Thismiaceae) with four new species from Borneo

Abstract

Fairy lanterns (Thismia Griff.) is a genus of poorly known mycoheterotrophic plants with unclear infrageneric classification. Commonly used approaches that utilize just a single or few traits in higher-level taxonomy lead to an apparently artificial system. In this contribution, four new species from Sarawak, northern Borneo, are described and illustrated. Thismia acuminata, T. laevis and T. nigra belong undoubtedly to section Sarcosiphon. Thismia viridistriata exhibits a high morphological variability with some individuals fitting section Scaphiophora based on the presence of a column on the top of the mitre, but otherwise perfectly matching the morphological characteristic of section Sarcosiphon. Five-locus (SSU, ITS, LSU, matR, atpA) phylogeny inference revealed paraphyly or polyphyly in the studied infrageneric taxa and showed that the importance of some traits traditionally used in Thismia taxonomy was overestimated. Most of the markers provide comparable phylogenetic signal; LSU performs best and is highly recommended for further phylogenetic studies. On the other hand, ITS is hypervariable and thus informative only within (sub)sections, as well as on intraspecific level, as proven in T. viridistriata with two distinct ITS (and also LSU and matR) alleles and two morphotypes within a small geographic area, which leads to an assumption of strong reproductive isolation even among nearby populations. For delimitation of species, the key trait appears to be the structure of the connective and any of the molecular markers used here.