This genus of over 400 species has a wide distribution from Europe, throughout Asia and the Americas. It is however at its greatest diversity in the eastern Himalaya and adjacent areas, which are home to nearly 80% of all species. They include annuals and perennials and miniatures to much taller species. These occur in a range of habitats from alpine screes, moist shady woodlands to streamsides and peat bogs – as such it is difficult to make many generalisations about cultivation. However, they mostly appreciate cooler climates and don’t appreciate drying out.