Dietes grandiflora was recognised as the flower which graced the 1 cent stamp in the definitive series of Republic of South Africa postage stamps issued in November, 1974. It is a spectacular plant which grows mainly in coastal areas, from a few kilometres west of East London, inland as far as Qonce, (King William’s Town), and thence through Eastern Cape to KZN. In these areas the plant forms large clumps, growing in full sun or partial shade at forest margins, or in the shelter of taller shrubs on exposed slopes facing the sea.
In the past the species has been confused with Dietes iridioides, a somewhat similar plant with much smaller flowers. The two species are often found growing together at forest margins in the East London area, with D.iridioides preferring more shaded positions.
Dietes grandiflora is a perennial herb. The underground part of the plant is a short, creeping rhizome which is dichotomously-branched and a dense fan of leaves is borne at the end of each branch. The leaves are up to 1m long and the peduncles are slightly longer so that the flowers overtop the leaves.
The flowers are borne in clusters of three or four and each cluster is protected by several herbaceous sheathing bracts. The flowers open in succession and Marloth records that they are visited by honey bees and a large fly. The flowers have no particular scent and each on last for several days. Flowering is sporadic, mostly in spring and summer after rains and the buds often remain dormant for months before they open.
The seeds germinate readily and the plant may also be propagated by division of the clumps. Dietes grandiflora is frequently cultivated in South African gardens and is astonishingly hardy, even when planted in exposed situations the complete reverse of its native habitat.
The name Dietes was first proposed by R A Salisbury in 1812, and the name was chosen, from the Greek di (two) and possibly the Latin etum (a plant association) in reference to Dietes dual affinities with Iris and Moraea both belonging to the Iridaceae family.
There are five indigenous Dietes species, D.bicolor, D butcheriana, D.flavida, D.grandiflora and D.Iridiodes in South Africa, all occurring naturally in the eastern parts of South Africa. It must be noted that D.iridioides also occurs in the Knysna forests. All these species especially the yellow wild iris (D.bicolor) and the large wild iris (D.grandiflora), make attractive garden and landscape plants. The only other species in this Genera, D.robinsoniana is naturally found on forest margins and the tops of Mount Gower and Mount Lidgbird on Lord Howe Island, which is in the Tasman Sea between Australia and New Zealand. It is suggested that D.robinsoniana got to Lord Howe Island through dispersal from an African origin, possibly D.Bicolor.
Ref. Flowers of Southern Africa ~ Auriol Batten.