Zantedeschia aethiopica is an herbaceous perennial that reaches about one metre in height. It grows in clumps from a short, underground stem with leaves that are broad, dark green and arrow shaped. Given sufficient water, the leaves are evergreen but under dry conditions they are deciduous. Although the foliage has ornamental value, arum lilies are most highly valued in horticulture and floristry for their spectacular, white, vase-like ‘flowers’, which have distinctive elongated, yellow columns at their centre. The arum lily in a bouquet is however a false flower. The true Zantedeschia aethiopica flowers are tiny, packed in tight groups around the central column (spadix), and surrounded by a specialised petal-like bract (spathe).
Zantedeschia is monoecious with female flowers at the spadix base and male flowers along the rest of its length. Female flowers, which are pollinated by insects such as beetles, mature before the male flowers. As the fruits mature, the spathe withers, with the lower portion turning green. Mature fruits are orange, fleshy berries. As might be expected for an ornamental, cultivars have also been selected which vary in their spathe and spadix colours.
All parts of arum lilies are toxic because inside the cells there are distinctive, needle-like crystals (raphides) of calcium oxalate. The raphides may also have physical effects by causing localised irritation in the mouth when eaten.
Zantedeschia aethiopica, a native of southern Africa, where it is often found on the banks of streams and ponds. Arum lilies are also naturalised in many other parts of Africa, as well as North America and Australasia, where they may become invasive species. The genus Zantedeschia comprises eight species, most of which are native to southern Africa, including horticultural calla lilies, Zantedeschia elliottiana and Zantedeschia rehmannii. The generic name probably commemorates the Italian botanist Giovanni Zantedeschi (1773-1846), whilst the specific epithet aethiopica probably refers to Africa rather than specifically to Ethiopia.
The arum lily, first reported growing in the Chelsea Physic Garden in 1731 by Philip Miller (1691-1771), was probably introduced to continental Europe in the seventeenth century from South Africa. In the Amsterdam botanic garden, seventeenth-century Dutch botanist Jan Commelin (1629-1692) made an early observation of plant guttation. He reported that in overwatered Zantedeschia aethiopica, excess water ‘will distil away in drops from the point of the leaves, perfectly limpid and of an acrid taste’. The water droplets are associated with specialised structures on the leaves called hydathodes.
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