forest and open agricultural fields can also be found at some locations. In particular the southern side of the lake contains more lush vegetation and broad-leaf forest than the northern side, which has more cliffs and contiguous pine forest. The rare and endangered flower Anthericum liliago can be found along the lake's rocky shores. This is one of the northernmost locales where it grows. On Torpön island is Sweden's largest wych elm and at Asby, a few kilometres from the southern shores, grows Sweden's thickest spruce. The name Ydre, which was formerly applied to most of the area around Sommen, is interpreted to mean "place of yews". One locality in particular appears to be further associated with yews; this is Idebo along Norra Vifjärden. Some plants usually associated with carbonate rock areas appear as rarities near Sommen, since there are no known carbonate rock outcrops in the area. The plants are Vicia pisiformis and the orchids Ophrys myoides, Malaxis monophyllos and Herminium monorchis. Geology Geographically the lake lies within the South Swedish highlands at a place where the Sub-Cambrian peneplain is uplifted. The present landscape is one of a hilly joint valley terrain. Topography displays local height differences as large as 100 m. Granite weathered into grus can be found at various locations around the lake. Red granite is a common rock around the lake and various parts are covered with till, including ground till deposited during the Ice Age. During the Weichsel glaciation, glacier ice moved over the Sommen area from the north-northwest. Drumlin-like forms and crags are also found throughout the area around Sommen. The ice sheets brought in carbonate rock and sediment from more northern latitudes to the Sommen area, depositing carbonates near the southern shores. This has made soils there richer in calcium than those further south. Deglaciation Following its maximum extent about 20,000–17,000 years ago the Fennoscandian ice sheet began to shrink gradually. The ice sheet's northward retreat brought the ice-front to the area of Sommen about 12,000 years ago. At this point the ice remained locally stagnant as it melted, with ice persisting longer in valleys than in hills and ridges. Thus the ice-front during deglaciation is thought to have been highly sinuous. Stagnation of the ice led to the formation of hummocky moraine and glacifluvial deposits. With its water surface at 146 metres above sea level, Sommen is slightly above the highest postglacial