Zantedeschia odorata

P.L.Perry

Family: Araceae
Common names: scented arum (Eng.); soetvarkblom (Afr.)

 

Flowers and leaves

 

Zantedeschia odorata is a rare, winter-growing, white arum with a moderately sweet scent and attractive, arrow-shaped leaves. With careful attention to growth and dormancy periods, it performs well in cultivation.  

Description
This winter-growing, summer-dormant geophyte grows 0.75 1 m high and has a deep-seated rootstock known as a stem tuber. Its 5 or 6, broadly arrow-shaped, plain green leaves have undulate margins and are carried on prominent petioles (leaf stalks). The erect flower stem produces a white spathe (a large sheathing bract) which encloses a yellowish orange spadix, a finger-like organ along which the minute, unisexual individual flowers occur. The female flowers occupy the lower part of the spadix and the male flowers appear above them. Flowering takes place from late July to August and a moderately sweet scent is emitted.

The fruit is a berry with a pulpy outer covering which dries up when ripe, revealing several round, hard, light brown seeds.

The spathe of Zantedeschia odorata looks very similar to that of Z. aethiopica but differs in being narrower, and the spadix is much shorter. Z. odorata is also distinguished from Z. aethiopica by its different, sweet scent, and its flower stems bending over towards the end of the fruiting period, whereas those of Z. aethiopica remain more or less erect. Z. odorata has a very restricted distribution, see below, whereas Z. aethiopica is widespread throughout most of South Africa.

Single flower

Conservation status
The conservation status of Zantedeschia odorata is Rare, which means that it is not exposed to any known direct or plausible potential threat and does not qualify for a category of threat according to the criteria determined by the International Union for Conservation of Nature (IUCN). The plants are not currently threatened because of the protection they enjoy from the surrounding boulders amongst which they grow.

 Distribution and habitat
Zantedeschia odorata is endemic to a small area of the Bokkeveld Escarpment near Nieuwoudtville in the Northern Cape, occurring in Nieuwoudtville-Roggeveld Dolerite Renosterveld vegetation . The plants grow in small groups and are confined to dolerite outcrops where water collects in depressions amongst boulders in doleritic clay. The red-flowered Sparaxis pillansii (family Iridaceae) is one of many geophytic companion species endemic to dolerite outcrops where Z. odorata occurs.

The genus Zantedeschia has eight species ( Z. aethiopica , Z. albomaculata , Z. elliottiana , Z. jucunda , Z. odorata , Z. pentlandii , Z. rehmannii and Z. valida ) and its centre of diversity is in eastern Mpumalanga. These mainly spring- and summer-flowering plants are almost entirely confined to southern Africa, with the exception of Z. albomaculata subsp. albomaculata whose range extends as far north as Tanzania in East Africa.

Derivation of name and historical aspects
In 1826 the German botanist Kurt Sprengel (1766 1833) named the genus Zantedeschia in honour of the Italian physician and botanist Giovanni Zantedeschi (1773 1846), who published works on the flora of the province of Brescia in the Lombardy region of northern Italy. The first species to be described under this genus was Z. aethiopica , the common white arum lily, although it had earlier been known as Calla aethiopica when Linnaeus described it in 1753. It has been in cultivation in Europe since the 1660s and is one of the world's most familiar plants, having become widely naturalized in temperate and tropical parts. Using several summer-growing species, including the dwarf pink or white Z. rehmannii , the white Z. albomaculata and the yellow Z. pentlandii , an extensive range of Zantedeschia hybrids have been raised in New Zealand and California for cut flowers and bedding plants, as well as numerous brightly coloured dwarf cultivars for pot plant production.

Ecology
Zantedeschia odorata has a deep-seated rootstock which is always found wedged between dolerite boulders, a strategy evolved to obstruct access by Cape porcupines which are very partial to the tuberous stems. Active growth begins after the first autumn rains in April, continues through the winter months and flowering takes place from late winter to early spring. It is not precisely known what pollinates the flowers.

Fertilized flowers produce bright green berries which mature to yellow in early summer and contain the seeds. The fruiting heads are at first erect but their stems bend and become pendent in early summer, resulting in the fruiting heads touching the ground. When fully ripe, the berries detach, the outer pulpy layer surrounding the seeds disintegrates and the seeds lie dormant close to the mother plants until they germinate in autumn.

Fruiting heads

 

Uses and cultural aspects
Zantedeschia odorata has no known medicinal or magical uses. In ornamental horticulture, the plants are used to a very limited extent by specialist bulb growers as container or rock garden subjects. In their fresh state, all Zantedeschia species are poisonous due to the presence of calcium oxalate, a compound that forms crystals known as raphides. However, the cooked leaves of Z. aethiopica are used as a pot herb by some African and Indian communities in South Africa.

 

Flowers

Growing Zantedeschia odorata

 

Zantedeschia odorata adapts well to cultivation and is easily grown outdoors in temperate climates in rock garden pockets, raised beds and deep containers. Although it occurs in seasonally wet doleritic clay in the wild, this is not a requirement in cultivation, as long as it receives sufficient moisture from autumn to late spring. It requires a position in full sun and grows well in loam soils containing plenty of well-decomposed organic matter. Plant the tuberous stems in groups 5 8 cm deep in autumn, and water well. Once the leaf shoots appear, water well twice per week until the end of the flowering period. Unlike Z. aethiopica whose rootstocks are not adversely affected by moisture during the dormant period, it is most important that Z. odorata rootstocks are given a completely dry rest for the full duration of summer to prevent fungal rotting.


Propagation is best from seed as the plants do not readily form offsets. Sow seeds 5 mm deep in deep seed trays in autumn in a well-drained medium such as equal parts coarse river sand and finely milled bark or potting compost. Keep the sowing medium moist by watering with a fine rose, and fresh seeds will germinate within two to three weeks. At the beginning of their second autumn, pot them up into plastic nursery bags or pots and allow them to grow on for one year. At the beginning of their third autumn, place them in permanent containers, raised beds or deep containers. Flowers can be expected in the third year, if grown well.

The rootstocks require protection from porcupines, especially during the active growth and flowering periods.

References and further reading

  • Duncan, G.D. 2014. Zantedeschia odorata . The Gardener (April 2014): 34.
  • Du PLessis, N.M. & Duncan, G.D. 1989. Bulbous plants of southern Africa . Tafelberg, Cape Town.
  • Mucina, L. & Rutherford, M.C. 2006. The vegetation of South Africa, Lesotho and Swaziland. Strelitzia 19. South African National Biodiversity Institute, Pretoria.
  • Perry, P.L. 1989. A new species of Zantedeschia (Araceae) from the Western Cape. South African Journal of Botany 55(4): 447451.
  • Singh, Y., Van Wyk, A.E. & Baijnath, H. 1996. Taxonomic notes on the genus Zantedeschia Spreng. (Araceae) in southern Africa. South African Journal of Botany 62: 321324.
  • Victor, J.E. 2004. Zantedeschia odorata P.L.Perry. National Assessment: Red List of South African plants version 2013.1. Accessed on 2014/01/10.

 

 

Graham Duncan

Kirstenbosch National Botanical Garden

December 2014

 

 

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