Gladiolus aureus

Baker


Family:
Iridaceae (iris family)
Common name:
golden gladiolus
Threatened status: critically endangered


Gladiolus aureus

This delicate, cormous geophyte produces most striking golden yellow blooms in late winter and early spring. Unfortunately, it is on the verge of extinction in the wild.

Description
FruitsGladiolus aureus is a deciduous, winter-growing, summer-dormant plant, 400-600 mm high, producing three very narrow grey or greenish grey, strongly ribbed leaves that are covered with short, soft hairs. Its slender flower stem produces an unbranched spike of three to seven funnel-shaped, pale to bright golden yellow blooms with very narrow, cylindrical perianth tubes that widen suddenly in the upper part. The plant grows from a small globe-shaped corm that is surrounded by hard, light brown outer tunics. The fruit is an elliptical, dry capsule, producing numerous small, round seeds surrounded by a brown, membranous wing.

Distribution and habitat
Endemic to the southern Cape Peninsula, Gladiolus aureus is currently restricted to a single small population in fynbos, in seasonally moist, acid sandstone, in full sun. This last wild refuge is in a highly vulnerable position as it is situated in an area that falls outside the boundaries of formally protected reserves, and is surrounded by dense stands of alien Acacia and Pinus trees.

Conservation
During 1976, 1 100 seeds collected in the wild were deposited at the Wakehurst Place Seed Bank (now the Millenium Seed Bank) in the United Kingdom, to determine whether cold storage of seed as a measure of long-term conservation was possible. This proved successful and tests carried out several years later at the seed bank showed a germination of 99% at 11º C. Gladiolus aureus has been successfully cultivated at Kirstenbosch Botanic Garden for many years and is also being grown by several specialist bulb growers in several countries. Ideally its natural habitat should be formally protected, but should this not be possible, ex situ material could possibly be used to re-establish this species elsewhere, in suitable sites.

Derivation of name and historical aspects
The genus name Gladiolus is derived from the Latin gladiolus, meaning a small sword, and refers to the narrow, sword-shaped leaves produced by many Gladiolus species. The specific name aureus is taken from the Latin aurea, meaning golden-coloured.

Gladiolus aureus was collected for the first time by Mr C.B. Fair in the southern Cape Peninsula in 1894, and was described by the Kew botanist J.G. Baker in 1896. Although known from several populations in the past, it has always been a rare species, restricted to the southern Cape Peninsula.

Ecology
The flowers of Gladiolous aureus are probably pollinated by honey-bees that are attracted to their bright golden yellow flowers. The flowers appear from late winter to early spring (July to September in the southern hemisphere), and remain partially closed in cool, wet weather, only opening fully on warm, windless days. The ripe fruit is a dry, three-chambered capsule that splits longitudinally, allowing the light, aerodynamic seeds to be carried away by the wind.

Uses and cultural aspects
The only practical horticultural use this species has is as a subject for specialist bulb growers, as a container plant.

Growing Gladiolus aureus

Although a rare species, G. aureus is not more difficult to grow than most other winter-growing gladioli. It likes an acid, sandy growing medium such as three parts medium-grained river sand and one part fine acid compost or finely milled acid bark. The corms are best planted in 15 to 20 cm diam. pots in autumn and watered well every seven to ten days. The plants need a well-ventilated, sunny aspect, preferably receiving full morning sun and afternoon shade. When in flower the delicate stems need to be staked to prevent them from falling over in strong wind. As temperatures rise towards the end of spring, the growing medium should be allowed to dry out and the dormant corms are stored completely dry over the summer rest period.

Fresh seeds germinate readily within four to five weeks, and should be sown in late autumn, after cool weather has definitely set in. Under ideal conditions, flowers can be expected for the first time during the third growth season. Under cultivation, plants of G. aureus are not particularly long-lived, usually only lasting five to six years. In order to ensure adequate material is maintained, it should be regularly repropagated from seed, as cormlets do not form readily.

References and further reading

  • Duncan, G.D. 1981. Gladiolus aureus Bak.-its present position. Veld & Flora 67: 17, 18.
  • Duncan, G.D. 1987. Gladiolus aureus. The Flowering Plants of Africa 49: t. 1948.
  • Duncan, G.D. 2002. Just holding on-spectacular geophytes in peril. Veld & Flora 88: 142-147.

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Kirstenbosch National Botanical Garden
June 2004

 

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