Disa tripetaloides

(L.f.) N.E.Br

Family : Orchidaceae

Disa tripetaloides

Disa tripetaloides is a terrestrial evergreen orchid with beautiful white flowers. It grows along perennial mountain streams and on damp mountain slopes in the Western Cape to KwaZulu-Natal. This winter rainfall species flowers in November and marks the start of the flowering season.

Description
Plant in potDisa tripetaloides is a slender plant, 100-600 mm high. Plants develop a network of underground stems (stolons), forming dense clumps. The stolons are protection against floods, hence the dense populations found along stream banks. The 6-10 leaves are small, 6-140 mm long and form a basal rosette.

 

Leaves

The colour and the shape of the flower vary depending on the locality. The flowers are usually white with various shades of pink. The yellow form is rare and found in the Eastern Cape (Transkei). The flower fades to a lighter pink as it ages. The flowering stem is 150-250 mm long and develops from the centre of the plant. Flowers, 7-10, are carried closely or spaced out on the stem. Flowers are 25 mm wide and resupinate, meaning the lip faces downwards. The hooded dorsal (maiden) sepal, lateral sepals and petals are white and often dotted with purple spots.

Flower

It flowers from November to January from Western Cape to the southern part of the Eastern Cape. In the summer rainfall areas of the Eastern Cape to the southern part of Kwazulu-Natal, flowering occurs from June to September.

Conservation status
It is illegal to remove any indigenous orchids including Disa species from the wild; South African law protects them. Permission to collect orchids requires a permit from the relevant Nature Conservation authorities.

Distribution and habitat
Disa tripetaloides is found growing in Table Mountain Sandstone habitats from the Hottentots Holland Mountains to KwaZulu-Natal. It occurs along fast-flowing perennial streams, mountain seeps and on banks and often submerged in nutrient-poor water during winter.

Derivation of name and historical aspects
Bergius described the genus Disa in 1767. The genus consists of 162 species. It occurs throughout Africa, Madagascar, Reunion, and a large number of species are found in south central and South Africa. In 1981, the genus Disa was taxonomically revised by H.P. Linder.

Ecology
Disa tripetaloides, a winter rainfall species, occurs from sea level to an altitude of 1 000 m. During the rainy season, plants are often found growing in cold, nutrient-poor water. In summer when temperatures are warmer, moist air is carried from the sea and rises over the peaks of mountain ranges. Clouds develop and the moisture from the clouds gives water to the streams.

The fleshy roots of the plant act as a storage tuber, helping the plant to beat drought during the dry summer season. It does not tolerate severe frost.

Disa uniflora is the most well-known species, and known as the red disa, flower of the gods, or the pride of Table Mountain. It bears the largest flowers in bright red to orange, carried on a flowering stem up to 600 mm long. Other evergreen species growing along stream banks, seepage areas and near waterfalls are D. aurata, D. cardinalis, D. caulescens, D. racemosa and D. venosa. They do not occur together but grow in similar conditions at different altitudes. The Mountain Butterfly, Meneris tulbaghia, which is attracted to the colour red, pollinates Disa uniflora.

Uses and cultural aspects
Disa tripetaloides is used successfully in hybridization and has produced numerous beautiful orchids. They are ideal pot plants and can be displayed as centrepieces on tables. etc. The flowering stem can be used in floral arrangements and will last 3-4 weeks.

Flowers

Growing Disa tripetaloides

Disa tripetaloides is said to be the easiest evergreen species to cultivate. Growing indigenous orchids requires dedication, time and attention throughout the year. It is important to study and understand the natural habitat, climatic conditions and the growth cycle of the plant; this will assist you in growing, maintaining and cultivating the plant successfully.

During winter the plant growth is slow and speeds up as the temperature increases during spring and summer. In late spring (late October beginning November), Disa tripetaloides develops a flowering stalk from the leaf rosettes, indicating the beginning of its flowering season.

Disa tripetaloides grows in full sun on mountain slopes and similar conditions should be maintained in cultivation (nurseries). The ideal temperature in greenhouses is 24C. Plants can tolerate winter temperatures of between 5-15C and summer temperatures should not exceed 30C. To keep the greenhouse cool, hose it down with water. It is important in cultivation to keep the soil and roots cool. Do not allow plants to dry out. Optimum humidity is 60%. Good air movement is essential, as hot, dry air or winds are fatal to the plants. During the spring and summer (growing season) exposure to bright light or filtered sunlight contributes to healthy plants and flower colour development. Place the plants on benches or metal racks erected against the wall to hold drip trays covered with shade cloth.

Plants are grown in 10-15 cm pots, filled with a well-drained soil medium of silica grit, palm peat and sand. A coarse medium encourages good drainage and prevents waterlogging. A layer of stone chips is placed at the bottom of the pot to encourage good drainage and aeration. Watering should be done early in the morning. The pH value of the water ranges between 5 and 6 (acidic) and should be low in salt. Watering depends on the season. In summer, water 3 to 4 times a week and in winter watering is reduced to twice a week, preventing fungal and bacterial rot. Ordinary tap water can be used, ensure it is not heavily chlorinated. Fill a bucket of water overnight to allow chlorine to evaporate before use. Over-watering can result in a soggy medium causing root rot. Apply overhead watering, using a hand-held hose, sprinkler or watering can.

Feed plants during the active growing season (early spring to summer) as temperature and light intensity increase vegetative growth and photosynthesis. Feed with an inorganic fertilizer. Apply a foliar feed once a month. At this stage, plants absorb more nutrients, mature, and become more vigorous and robust. After the flowering spike emerges, the plant develops a new tuber. After the flowers have died, the flower stem turns yellow and dies back and the excess nutrients are absorbed by the replacement tubers.

The tuber takes about three months to develop healthy roots and leaves. The new plant will flower in the next season. Its survival depends on the development of the tuber and over-feeding prevents it from developing. Stop feeding it once the flowers have wilted. Excessive application of nitrogen is detrimental, causing the plant to develop weak flowering stems, lax and soft growth.

Re-pot in autumn once the flower stalk has died and new growth is vigorous. Remove old soil, decaying roots and the old tuber, wash in a fungicide, add new soil and water.

Disa tripetaloides produces stolons (underground stems) which give rise to new plants and tubers. Plants form clumps of 4-6 individuals that can be divided during re-potting.

Sow seeds in autumn on washed peat or sphagnum moss. Fill the bottom of the pot with a layer of stone chips, a mixture of silica grit, sand and peat and top up with a layer of peat. Water well and sow a thin layer of seeds on the surface. Spray with a suitable fungicide, e.g. Kaptan. Use clear plastic to cover the pot, held in place with a rubber band, or use a clear pane of glass. Place in a shady position and germination will take place after four weeks.

Keep medium moist, by placing the pot in a tray of water. Pots can also be soaked in a bucket of water, but do not allow the seeds to float in the water, or use a spraying can. Regular inspection will detect any fungal infection or diseases and treat with an appropriate fungicide. Remove the plastic cover or glass gradually as the young seedlings develop. Once the covering is removed and plants have adapted to the environment, prick out the seedlings and pot. Transfer the year-old seedlings into a fresh medium consisting of equal parts coarse river sand and peat and keep under shade; they will grow rapidly during the second year. The first flower forms during the third year. Re-pot every year.

Aphids, red spider mite, caterpillars and gall midge fly are common pests of disas and are treated successfully using the correct insecticides and application rates. The presence of red spider mite and thrips indicate that the environment is too warm for the disas. A cooler environment will reduce their activity. Warm, dry, humid conditions cause diseases such as crown rot and damping off-treat with a suitable fungicide. Keeping the environment clean, removing dead or rotted leaves and avoiding over-watering will reduce pest and disease attacks.

References and further reading

  • Crous, H. & Duncan, D. 2006. Grow disas. Kirstenbosch Gardening Series. South African National Biodiversity Institute, Cape Town.
  • Goldblatt, P. & Mannning, J. 2000. Cape plants. A conspectus of the Cape flora of South Africa. Strelitzia 9. National Botanical Institute, Pretoria & Missouri Botanical Garden, Missouri.
  • Hitchcock, A.N. 1989. Cultivation of Disa uniflora. National Botanical Institute, Kirstenbosch, Cape Town.
  • Linder, H.P. & Kurzweil, H. 1999. Orchids of southern Africa. Balkema, Rotterdam.
  • Steward, J., Linder, H.P, Schelpe, E.A. & Hall, A.V. 1982. Wild orchids of southern Africa. Macmillan, Cape Town.
  • Wodrich, K. 1997. Growing South African indigenous orchids. Balkema, Rotterdam.

 

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