Rhinanthus osiliensis

Rhinanthus osiliensis is strictly endemic to the western part of Saaremaa island, Estonia, with a highly restricted geographic range. The species is a habitat specialist that primarily inhabits calcareous spring fens, which are naturally scarce wetland habitats. It also occurs in other wetland environments such as species-rich fens and paludified meadows. The plant can temporarily colonize marginal habitats like ditch verges and stream banks, though such populations tend to be transient. As an annual hemiparasitic plant, R. osiliensis attaches to and derives nutrients from the roots of perennial herbaceous host plants. The species typically begins flowering in the second half of July and early August, with pollination carried out by insects, particularly bumblebees. Its seeds, which ripen by late September or early October, are relatively large and heavy, lacking an active dispersal mechanism. Consequently, most offspring are found in close proximity to the parent plant. The seeds generally maintain viability for only one year, and the species does not form a persistent seed bank. The population of R. osiliensis was estimated at about 26,000–32,000 individuals as of 2010, distributed across several dozen established populations. Many of these populations are located within nature reserves. …