This large genus from (almost entirely western) North America is said by some to rival Primula, Gentiana and Saxifraga as a prime genus for the rock garden. We don't rate it quite that highly, but it includes many splendid plants, with the virtue of flowering later than most inhabitants of the rock garden. They range from low mats and cushions from high mountains to tall plants used in herbaceous border, and include both shrubby and herbaceous species, although most are evergreen. The flowers are 'foxglove' like, usually in spikes or arranged in whorls, technically called verticillasters. Virtually all are from rocky places, and require very well drained, gritty soil, with maximum sunshine. Some need protection from excessive winter wet, but those we list are generally easy plants for outdoor cultivation. The rock garden species are inclined to die back after some years, so it is wise to propagate one or two replacements by taking cuttings or separating pieces of the mat.