With its unusual flowers, attractive shape and ease of cultivation, the yellow wild iris is a versatile garden plant.

The genus name "Dietes" is derived from the Greek "dis" which means twice and "etes" which means an associate and is drawing attention to the position of this genus between Moraea and Iris which are its two relatives. The species name "bicolor" means two-coloured.

Dietes bicolor forms clumps of erect sword-shaped leaves. The adult plant is approximately 1m wide and 1m tall. The leaves are 1 to 2cm wide, light green in colour and have a double central vein. They are arranged in flat fans similar to other members of the iris family. The plant spreads by means of its modified stems (rhizomes), which are located below the soil surface.

The flowers are about 60 mm in diameter, flat, light yellow with brown markings and are produced on the ends of much branched flower stalks. The flowers only last for one day, but because so many buds are produced the plant is almost always in flower from October until January (spring and summer). The fruit is a club-shaped capsule approximately 25mm in diameter which partially splits to release the seeds.

The flower of Dietes bicolor is made up of three functional units, each consisting of an outer tepal and a style branch. Each of these units must be entered separately by the pollinating insect (probably a bee). Nectar is secreted at the base of each of the outer tepals. When the insect pollinator pushes itself between the outer tepal and style branch in search of nectar, the pollen is deposited on its back and as it moves from plant to plant it spreads pollen from one flower to the other resulting in pollination.

The insects, in turn, attract various insectivorous birds to the garden. Joffe (2001) reports that the roots of D.bicolor were traditionally used as a charm to protect the strengthen the wearer.

The genus Dietes is only found in South Africa and on Lord Howe island between Australia and New Zealand. D. bicolor is found naturally in the Bathurst region of the Eastern Cape in South Africa. An interesting fact about Dietes is that of the six species that are known, five of them occur in the eastern parts of South Africa with one on Lord Howe island namely D. robinsoniana. The most primitive of these (according to molecular analysis) is D. bicolor followed by D. robinsoniana on Lord Howe island. This suggests that D. robinsoniana got to Lord Howe island through dispersal from an African origin, although how this could have happened is at present unknown.

Growing Dietes bicolor

The yellow wild iris is fast growing which makes it ideal for use in areas that need to be established rapidly. Although it occurs naturally near streams and in marshy places, it is also drought resistant and frost hardy. Dietes bicolor forms a large spiky clump, ideal for use as an accent plant near ponds or at the sides of steps, pathways and entrances. Because the plant multiplies rapidly, it can be easily propagated for large scale plantings. Its evergreen, spreading habit makes it suitable for use as a long lasting groundcover. The flowers are not suitable for cut flower arrangements as they are so short lived. The plant is able to grow easily in very poor soil with little water and can be useful when plants need to be established on poor subsoils as is often the case after earth moving has taken place on building sites. The yellow wild iris is often mass planted on road islands.

The plants also thrive in damp situations and will tolerate light shade, but do better in full sun except in hot inland gardens where partial shade is best. For optimal results plant the yellow wild iris in soil containing plenty of compost and water regularly. The yellow wild iris has been cultivated in Europe since the early 1800's.

Dietes bicolor can be propagated by dividing the rhizomes of large clumps after the flowering period or in autumn. The seed of the plant germinates readily when sown in spring or autumn in a good, moist seedling medium.

Dietes bicolor belongs to the family Iridaceae (iris family). These plants are perennial herbs in the form of either rhizomes or corms. There are about 82 genera and 1700 species belonging to Iridaceae. Over half of the species of Iridaceae occur in South Africa, in 38 genera. Plants in the family Iridaceae have sword-shaped leaves which are arranged in 2 ranks (a row, especially a vertical row). The flowers are regular or irregular with 3 stamens and an inferior ovary. The genus Dietes (wild iris) is a perennial evergreen which used to be included with Moraea (another member of the iris family) but was separated owing to the nature of its growth. Dietes do not have corms as are found in Moraea, but have a rhizome. Several other Dietes species, including D. grandiflora make good garden plants.

Reference

• Eliovson, S. 1984. Wild Flowers Of Southern Africa. 7th edition, Pretoria:
• Joffe, P. 2001. Creative Gardening With Indigenous Plants.: A South African Guide. Pretoria: Briza.
• Joffe, P. 1993. The Gardener's Guide To South African Plants. 1st edition, Cape Town: Tafelberg Publishers Limited.
• Manning, J. 2002. Personal communication via email. Compton Herbarium, National Botanical Institute, Cape Town.
• Pooley, E. 1998. A Field Guide To Wild Flowers Kwazulu-Natal And The Eastern Region.
  1st edition, Durban: Natal Flora Publications Trust.
• Van Der Spuy, U. 1971. Wild Flowers Of South Africa For The Garden. 1st edition,
  Johannesburg: Hugh Keartland Publishers

Marc Stern
Witwatersrand National Botanical Garden.
June 2002