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The occurrence of mountain plant species in the Polish lowlands has been at the centre of attention of many botanists. In 2008-2011 we carried out field studies aimed at describing a new lowland population of White Twisted-stalk S. amplexifolius discovered in 2008. We focused on the following aims: to determine the current status of the lowland population of S. amplexifolius; to characterize phytocenoses and habitat conditions in which the species occur; to identify factors that can potentially pose a threat on the population and to propose guidelines for its protection. The newly discovered population is located in the Trójca Forest District (50º 38.737’ N; 18º 48.945’ E), forest department 61L. The main part of the population (ca. 70%) occupies an area of approximately 100 m2. Currently, to protect the population from grazing, the whole area (about 0.25 ha) has been surrounded by metal mesh fence. The population occurs within a poorly developed patch of Fraxino- Alnetum. It contains 107 branched and fruiting individuals of S. amplexifolius and 83 smaller plants (branchless and sporadically fruiting). The number of fruits per plant varies between 6 and 20. One fruit contains an average of 5 seeds (a maximum of 12 seeds and a minimum of 3 seeds per fruit). The occurrence of numerous Padus serotina seedlings and young plants is recorded within the site. Human-related factors have caused substantial changes in the water relations and, subsequently, also in the species composition of these plant communities. The population of S. amplexifolius within the described site seems to be in good condition and develops normally.

The etiology of a previously unknown disease of Streptopus amplexifolius (L.) DC. (twisted stalk) that occurred in south central Alaska was elucidated. Symptomatic plants with yellow-green dashes and streaks on their leaves contained distinct viruses belonging to the family Potyviridae and (or) tentatively to the family Flexiviridae genus Carlavirus . Each virus' identity was confirmed by a combination of morphology, serology (ELISA and (or) Western analysis), and sequences obtained from reverse transcriptase - polymerase chain reaction products previously generated by potyvirus- or carlavirus-specific primers. The mechanical transmission of particles (purified from twisted stalk as a mixture of both viruses or as a single preparation of each virus) to S. amplexifolius, Chenopodium amaranticolor Coste et Reyn, and Chenopodium quinoa Willd., fulfilled Koch's postulates. The relatively high incidence of infected plants and associated severe symptoms in populations from several sites in south central Alaska gave evidence that native plants are susceptible to, and are adversely affected by viral diseases. Even though Streptopus species grow throughout the temperate regions of the world, this is the first report of a pathogen(s) infecting plants in the genus Streptopus.