Another plant which we tend to bring into our houses during the festive season is mistletoe.
The European mistletoe (Viscum album) is at the basis of a variety of kissing customs and has connection with ancient Norse and Druid folklore.
However, this plant has a fascinating life-style.
It is a parasitic plant, without roots attached to the ground. Instead it attaches itself to a host tree, and gains water and minerals from the xylem of that tree and possibly photosynthetic products from the phloem. There are many different species of host plant, and the dominant host species vary in different parts of Europe.
It does, however, carry out photosynthesis and remains green throughout the winter. Perhaps this is the basis for some of the mythology surrounding it and its association with winter ceremonies.
The fruits of mistletoe are white berries containing a sticky substance - the basis for the word viscous.
Mistletoe seeds are spread by birds, presumably wiping their beaks on branches on which they are perching. The germinating seed sends its root through the
bark of the host tree, forming a structure called a haustorium which enables it to extract liquids from the vascular tissue of the host species.
As a consequence, mistletoe plants grow in almost spherical colonies, often visible on tree branches high above the ground.
Globally there are many species of related plants, and some are seen by foresters as pests on account of their demand for water causing stress to their host plant during dry seasons. In Australia, there are several species of butterfly the caterpillars of which live only on certain mistletoe species.