SA Orchids: Disa

Disa unifloraDisa (including Schizodium) is a very large African genus and is represented in southern Africa with 144 species. There are many widespread ones, but some are endemic to rather small areas and a few are even known from only one collection made many decades ago. Disa species are found in fynbos, on rock flushes, in marshes and vleis and in montane and subalpine grassland. Their brightly coloured flowers place them among the more attractive plants in these habitats, although their flowers are often only medium-sized or small. A remarkable exception is the spectacular D. uniflora with its large, brilliant red flowers.

While some species are rarely seen as they are scarce and quite localized in their area of occurrence, others are rather common and can be quite plentiful in some areas. Colonies with hundreds or thousands of individuals can sometimes be seen, especially if the area has recently been burnt.

Disa species generally occur in both southern African rainfall regions. The pollination of Disa species is very diverse, ranging from self-pollination through to pollination by bees, hawkmoths, butterflies and small flies. Flowering occurs in spring and summer.

The name Disa probably originated in the Swedish mythology. Sweden is where J. Bergius lived, the botanist who described the genus Disa in 1767 based on a specimen of D. uniflora. We think that Bergius noted the net-like veins of the sepals of the red disa, thus reminding him of an old tale in which Disa, a young woman, came to the king dressed in a fish-net.

Description

Disa species have round to elongate root tubers. Their stems range from slender and only 5 cm tall to robust and one metre in length. They can have leaves up the stems or only at the base. Leaves range from linear to lanceolate. Some of the species have sterile stems with foliage leaves, while their flowering shoots arise from separate leafless stems. Inflorescences may form spikes or clustered heads (elongate-racemose or capitate), but they are always unbranched.

The flowers, which are mostly resupinate (lip faces down), come in colours ranging from pink, white, blue, red and yellow to brown, and frequently have darker markings. The medium sepal is always hooded with a spur up to 10 cm in length. In some species the spur is reduced to a sac, and occasionally it is missing altogether. The petals may be erect or reflexed next to the column to which they are basally fused. The lip is normally a very small and slender organ. However, in a few species it is ovate and rather wide, and sometimes also marginally deeply dissected. The column in the centre of the flower lacks an elongate basal stalk. It has a reflexed or sometimes erect anther, and a stigma resembling a small cushion.

Disas, except for the Disa uniflora group, are deciduous.

Disa uniflora Group

Disa uniflora, D. tripetaloides, D. cardinalis, D. aurata and D. caulescens are mainly found in the Western Cape mountains, always growing associated with perennial water - growing on the edges of perennial mountain streams or in wet moss near waterfalls, at altitudes varying from sea level to approximately 1200 m. Although these species do not occur together, the preferred habitats are very similar and only vary in altitude. The soil that the plants are found in is either a sand derived from Table Mountain Sandstone with organic silt trapped in it or an organic fibrous humus well impregnated with sandy silt. Both substrates have extremely good drainage properties.

The most popular Disa species is D. uniflora, commonly known as the 'pride of Table Mountain', 'flower of the gods' or simply 'red disa'. In the Western Cape there are quite a few schools, roads, shopping malls or garden centres named after the genus Disa, all alluding to this species. Furthermore, the flower of this species is depicted in the emblems of the Mountain Club of South Africa and the Western Province Rugby Union.

Disa uniflora is fairly common in suitable habitats and plants often grow in clusters of numerous individuals. The leaves are mainly basal and lanceolate, and unlike in other Disa species, they are evergreen. D. uniflora has very large brilliant red or orange flowers (up to 12 cm in diameter), and also yellow forms are very rarely found in nature. The flowers are borne on stems up to 60 cm long. Although most plants have only one or two flowers, individuals with six or eight flowers have been recorded.

In summer various hiking clubs and museums organize trips on Table Mountain near Cape Town to look at the red disa.

D. uniflora is pollinated by the large 'Mountain Pride' butterfly which is strongly attracted by the red colour, whether seen in flowers, hiking socks, T-shirts, backpacks or elsewhere (red is a colour which many other insects cannot see). The disa species is only one out of about 15 plant species pollinated by this butterfly which evidently has a passion for red, but ignores flowers with other colours. This explains why an extremely rare yellow mutation of the 'red disa' cannot survive in nature as its flowers are not pollinated by the butterfly; once the mature plant has died the yellow form disappears as there is no seedling recruitment (the yellow mutant is not very vigorous like most other mutants in the plant kingdom, and therefore is not very long-lived).


How to grow disas

Selected species and their main distribution
Winter-rainfall area: D. obtusa, D. comosa (previously Monadenia comosa), D. ophrydea (previously Monadenia ophrydea), D. draconis ('white disa'), D. ferruginea ('cluster disa'), D. spathulata ('oupa-met-sy-pyp'; previously Herschelianthe spathulata), D. graminifolia ('blue disa'; previously Herschelianthe graminifolia), D. purpurascens ('early blue disa', 'bloumoederkappie'; previously Herschelianthe purpurascens), D. barbata ('ouman-met-sy-baard'; previously Herschelianthe barbata), D. uniflora ('pride of Table Mountain', 'flower of the gods', 'red disa'), D. racemosa ('rose disa'), D. tripetaloides, D. rosea, D. bivalvata, D. tenuifolia ('yellow disa'), D. longicornu ('drip disa'), D. subtenuicornis, D. uncinata, D. harveiana, D. tenella, D. multifida, D. vaginata, D. reticulata, D. hians
Summer-rainfall area: D. chrysostachya, D. fragrans ('lekkerruik-disa'), D. crassicornis, D. cooperi, D. versicolor ('apple blossom orchid'), D. saxicola, D. stricta, D. pulchra ('moederkappie'), D. stachyoides, D. caffra
Both areas: D. cornuta ('golden orchid'), D. bracteata (previously Monadenia bracteata), D. cylindrica, D. sagittalis


Click images below to enlarge

Disa obtusa
D. obtusa
Disa subtenuicornis
D. subtenuicornis
Disa uncinata
D. uncinata
Disa ophrydea
D. ophrydea
Disa draconis
D. draconis
Disa harveiana
D. harveiana
Disa ferruginea
D. ferruginea
Disa tenella
D. tenella
Disa longicomu
D. longicornu
Disa stachyoides
D. stachyoides
Disa multifida
D. multifida

D. graminifolia
Disa reticulata
D. reticulata
Disa vaginata
D. vaginata
Disa hians
D. hians
Disa chrysostachya
D. chrysostachya
Disa cornuta
D. cornuta
Disa stricta
D. stricta
Disa caffra
D. caffra
Disa pulchra
D. pulchra
Disa fragrans
D. fragrans
Disa saxicola
D. saxicola

 


Author: Hubert Kurzweil
Images: H Kurzweil, O Kurze, H Boernitz, J Manning
October 2000
(Updated by Clare Archer, August 2010)


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