Saturday 11 September 2010: Arum
"Zantedeschia is named after Professor Zantedeschi, probably Giovanni Zantedeschi, 1773-1846, an Italian physician and botanist, although there is some uncertainty about this. The name aethiopica is not directly related to Ethiopia, or Africa. Although called the arum lily, it is neither an arum ( the genus Arum) nor a lily ( genus Lilium).
The 'Marshmallow' with a creamy pink spathe (outer "petal" which is actually a modified leaf) and rose-pink throat and the 'Green Goddess'with a green and white spathe. There is also an attractive form with leaves spotted white.
This lovely plant was introduced to Europe very early on, apparently before Van Riebeeck had established the refreshment station at the Cape. It is also illustrated in an account of the Royal Garden in Paris in 1664. It was sent as one of the interesting plants of the Cape to Europe by Simon van der Stel some time before 1697.
The striking arum lily "flower" is actually many tiny flowers arranged in a complex spiral pattern on the central column (spadix). The tiny flowers are arranged in male and female zones on the spadix. The top 7 cm are male flowers and the lower 1.8 cm are female. If you look through a hand-lens you may see the stringy pollen emerging from the male flowers which consist largely of anthers. The female flowers have an ovary with a short stalk above it, which is the style (where the pollen is received). The spadix is surrounded by the white or coloured spathe.
The flowers are faintly scented and this attracts various crawling insects and bees which are responsible for pollinating the flowers. A white crab spider of the family Thomisidae visits the flower to eat the insects. This spider does not spin webs and uses its whiteness as camouflage against the spathe. In the western Cape, a tiny frog Hyperolius hopstocki is also attacted to the arum lily flowers.
The spathe turns green after flowering and covers the ripening berries. It rots away when these are ripe and the succulent yellow berries attract birds, which are responsible for seed dispersal.
The leaves of the arum are very interesting in that they contain water stomata which can discharge excess water, by a process known as "guttation". This prevents water-logging and enables arum lilies to grow in wet conditions.
The rhizome is large and eaten by wild pigs and porcupines and the ripe fruit enjoyed by birds. Traditionally the plant is boiled and eaten. Raw plant material causes swelling of the throat because of microscopic, sharp calcium oxalate crystals. The leaves are also traditionally used as a poultice and a treatment for headaches.