Nigritella lithopolitanica Ravnik (Orchidaceae): morphological and ecological differences among populations and factors contributing to its endangerment

• Published in: Botany letters 2020-07, Vol.167 (3), p.353-362
• Main Authors: Sajna, Nina, Perkovič, Kaja, Paušič, Igor
• Format: Article
• Language: English
• Subjects: Alps; endemic species; plant ecology; plant traits; Slovenia; Vanilla orchid
• ISSN: 2381-8107; 2381-8115
• DOI: 10.1080/23818107.2020.1765196

The rare orchid, Nigritella lithopolitanica is endemic to species-rich mountain grasslands of the south-eastern Alps with the majority of its distribution area in Slovenia. We examined phenotypic variation in morphological and reproductive traits among seven of 16 extant populations in relation to the floristic composition and stature of the grasslands surrounding these plants. Inflorescence length varied the least among populations and was uncorrelated with either habitat characteristics or location. This stability presumably reflects its reliance on specialized pollinators. Other traits display appreciable variation among populations and covary with grassland composition and stature. Taller plants occur within taller swards and allocate more to vegetative growth and less to reproduction. The presumably reflects an adaptive trade-off to enable competitive success under competitive conditions. We conclude that N. lithopolitanica has low competitive potential and thrives best on sites with thin soils, some stone cover, and in open, low-density swards of vegetation where competing grasses are shorter. Grazing appears to favour this species whereas the recent human removal of stones from these habitats represents a clear threat to the persistence of this rare species.