Bog Arum is native to Denmark and other European countries, northern Asia and northern North America. It often grows in large stocks. It is seen here and there in bogs and fens, it is a characteristic plant of raised bogs. The Bog Arum has a characteristic inflorescence, where the flowers sit together in a yellow-green bulb, surrounded by a white spath. The plant is also known by the name vandkalla/ Water Calla, because it is similar to the Kalla-flower (which also belongs to the Arum-family). Other names are Arum lily / Calla lily / Water arum / Water dragon / Wild calla. The Latin name ”Calla” was by the ancient Romans used about another, unknown water plant. The name palustris means "growing in swamps."
In the autum the inflorescense is changed into a bulb of crimson berries. The leaves are heartshaped and shining lightgreen; leaves and inflorescense sit upon fleshy, lightgreen stalks, which form the juicy rhizomes. The plant cannot be confused with any other Danish plant. The whole plant and the berries are poisonous, it has a high oxalic acid content, but the rhizome is edible after drying, grinding, leaching and boiling. In Viborg, Jutland, it was in 1795 recommended to use the dried, crushed roots for flour.
Large stocks of bog arum can both form a *hængesæk out into the water or be spread upon land. It is therefore necessary to take care and not walk among the plants, since there is often water down under.
*Hængesæk: A socalled hængesæk is a society of plants, formed by entangled roots and stalks, which grow in the surface of a bog or across open water without connection to the bottom. The stock of plants might be so close that the water below the plants are not sensed. Old hængesække might carry the weight of a human, but not everywhere. It can be highly dangerous to walk out upon a hængesæk, a person can fall through and down under the plant cover.
The flower is polluted by insects, and the seeds are spread by birds, who eat the berries( the plant is hardly poisonous to the birds). It seems like the spread in Denmark is mostly vegetative, since pieces of the rhizome are introduced to other localities by water birds. The bog arum in Denmark is common in northeast Sjælland (Zealand) , but it is rare in other parts of Denmark. It is now and then seen plant in garden ponds etc.
The Danish name Kærmysse: 1793, the syllable mysse might origin from Norwegian myr = mose/moor. It was also called water-ginger in Denmark, since the root and seeds tasted like the spice ginger, and it had the name kalla in many connections, because it looked like the kalla-houseplant.
Some plants from tropical Africa, often termed "calla lilies", have now been transferred to the genus Zantedeschia and should not be confused with Calla palustris.
V.J. Brøndegaard, Folk og Flora, Dansk etnobotanik, Rosenkilde og Bagger, 1980. Danmarks fugle og natur, Felthåndbogen, 2012; haveabc, Danmark; Liber herbarum.
photo: Aqua Mose, Silkeborg 2009: grethe bachmann