Gladioli are popular garden plants, cultivated in Europe for more than 250 years and renowned for their striking, colourful flowers. But did you know that these garden plants were grown from hybrids of wild gladioli native to South Africa? Gladiolus oppositiflorus, with its large, showy flowers is an important species in the breeding history of a number of Gladiolus hybrids, but is also an attractive garden plant in its own right.
Gladiolus oppositiflorus is a summer-growing plant, 0.6-1.6 m high, with aboveground parts disappearing during winter. Roots, leaves and flowers develop from an underground corm, which is a swollen part of the stem serving as a storage organ when the plant dies back during winter. Leaves are long and narrow, and resemble the shape of a sword, which is where the genus derives its name.
.The flowering stem is tall and straight, with flowers developing in succession from the lower end towards the tip, and is called a spike. Successive flowers face in opposite directions. The flowers are large and funnel-shaped, with long, narrow, curved perianth tubes. Flower colour varies from white, to mauve, pale or salmon-pink, with the lower petals (tepals) marked with dark red streaks. Flowering time varies between different areas of the species' native range, with some flowering from November to December, and others from February to March. The fruit is an oblong, three-lobed capsule and the small (4-6 mm), round seeds are winged.
Gladiolus oppositiflorus is a representative from the Pondoland Centre of Plant Endemism, located in a small area between the Mzimvubu River, near Port St Johns, and the Umtamvuna River, near Port Edward, within the region known as the Transkei Wild Coast. This is an area of great natural beauty, and many rare and unusual species are found here. Because a high number of species are concentrated in such a small area of only about 180 000 hectares, the Pondoland Centre of Endemism is acknowledged by international conservation organizations such as the World Conservation Union (IUCN) and the World Wildlife Fund for Nature (WWF), as one of 235 world-wide centres of plant diversity. Another international organization, Conservation International, included the Pondoland Centre among only 25 global hot spot sites (see CI hotspots ), in need of special conservation efforts. However, locally, very little is being done to conserve the Pondoland floral riches. Only a few small nature reserves exist within the area, and although negotiations have been going on for years, no national park to conserve the Pondoland Centre has been established to date. Meanwhile the Pondoland Centre faces severe threats from dune mineral mining, overgrazing, illegal holiday cottage developments and a proposed toll road connecting Durban and East London which could dissect the most sensitive areas of the Centre containing more than 200 endemic or near-endemic plant species.
Distribution and Habitat
Gladiolus oppositiflorus is endemic to the summer rainfall regions of the Eastern Cape north of East London to southern KwaZulu-Natal, from the coast to as far inland as the Lesotho border. It is found in rocky areas in open grassland, often among rocks along streams.
Derivation of name and historical aspects
The genus name Gladiolus comes from the Latin word gladius, meaning sword, and refers to the shape of the leaves of all members of the genus. The species name oppositiflorus refers to the opposite-facing flowers, but this is not a unique characteristic to this species, as some closely related species such as G. elliotii and G. sericeovillosus also have opposite-facing flowers.
The species was first mentioned in horticultural literature in 1837 by the Rev. William Herbert (1778-1847), theologian, linguist, poet, amateur botanist and father of the English novelist Henry William Herbert. Herbert experimented with breeding garden hybrids from wild species of Gladiolus. The salmon-pink variety of this species is found further inland on the lower slopes of the Drakensberg, and is somewhat shorter-stemmed than the coastal form, the flowers do not open as widely and the inland variety is always deciduous whereas the coastal form is often evergreen. They were long thought to be two different species, or subspecies, with the salmon-pink variety called G. salmoneus by J.G Baker (1896). A.A. Obermeyer (Lewis et al . 1972) classified it as G. oppositiflorus subsp. salmoneus in her revision of the genus. Therefore, in many older gardening publications the two forms are referred to by separate common names, with the coastal form called Transkei gladiolus, whereas the salmon-pink, inland form is called salmon gladiolus. Goldblatt & Manning (1998) found that the two forms integrate in the central Eastern Cape and therefore they are currently considered to be a single species.
Gladiolus oppositiflorus is pollinated by species of flies with elongated mouthparts, also called long-tongued flies belonging to the family Nemestrinidae, the tangle-veined flies. The mouthparts of these flies can be several times longer than the body length of the fly, and is ideally adapted to reach nectar at the bottom of the long narrow perianth tube. The specific lengths of the flies' mouthparts vary according to the length of the perianth tube of the flowers they pollinate. The dark red markings on the lower parts of the flower are there to guide the insect towards the inner parts of the flower and are called nectar guides. Although the flies may visit different species of flowers with elongated perianth tubes, pollen does not get mixed between different species. This is because the structural arrangement of the floral parts are adapted so that pollen is only deposited on very precise parts of the fly's body, and each species deposits pollen on a unique part of the insect's body. This prevents the clogging of stigmas with foreign pollen, which will prevent fertilization and seed set, and also prevents the formation of natural hybrids between wild species.
Uses and cultural aspects
Gladiolus oppositiflorus has no known traditional or medicinal uses, but is highly regarded as a very attractive garden plant and cut flower.
Growing Gladiolus oppositiflorus
Gladiolus oppositiflorus is relatively easy to grow, and can be cultivated from corms as well as seeds. It should preferably be planted in light, well-drained, sandy loam soil in full sun. As this is a summer-growing species, plant corms in spring (around September) and give plenty of water all through the growing season. Corms are best planted in open ground, rather than pots, roughly 10 cm deep and 15 cm apart. Avoid the use of inorganic fertilizers, especially those with high nitrogen content. Rather use compost, and bonemeal can also be beneficial. The corms can be left in the soil during the winter dormancy period, or lifted and stored in a cool airy place to prevent decay.
When growing from seed, sow in September. The seeds generally germinate well and seedlings appear after two to four weeks. Water thoroughly all through the growing season. However, flowers will only be produced from the second season onwards.
Summer-growing Gladiolus species such as G. oppositiflorus are particularly susceptible to a wide range of pests, such as aphids, mealybugs and thrips, while red spider mites may become a problem when conditions are dry. G. oppositiflorus is also susceptible to rust, but avoid the use of copper-based fungicides.
References and further reading
- Baker, J.G. 1896. Flora Capensis 6:154
- Barnhoorn, F. 2005. Growing bulbs in southern Africa, edn 2. Struik, Cape Town .
- Bryan , J.E. 1989. Bulbs. Volume I, A-H. Christopher Helm Publishers, Bromley.
- Du Plessis, N. & Duncan, G. 1989. Bulbous plants of southern Africa : guide to their cultivation and propagation. Tafelberg, Cape Town .
- Eliovson, S. 1973. South African wild flowers for the garden, edn 5. Macmillan, Johannesburg.
- Goldblatt, P. & Manning, J. 1998. Gladiolus in southern Africa. Fernwood Press, Vlaeberg, Cape Town .
- Goldblatt, P. & Manning, J. 1999. The long-proboscid fly pollination system in Gladiolus (Iridaceae). Annals of the Missouri Botanical Garden 86: 758-774.
- Lewis, G.J., Obermeyer, A.A. & Barnard, T.T. 1972. Gladiolus : a revision of the South African species. Journal of South African Botany Suppl. 10.
- Nel, M. 2003. The extraordinary floral riches of Pondoland: Working towards a ' Pondo Park '. Veld & Flora 89: 96-100.
- Picker, M., Griffiths, C. & Weaving, A. 2004. Field guide to the insects of South Africa . Struik, Cape Town .
- Van der Spuy, U. 1971. Wild flowers of South Africa for the garden. Hugh Keartland Publishers, Johannesburg .
Pretoria National Botanical Garden