Oncidium astranthum - Star Flowered Oncidium flowers are stellate, 4 cm in diameter; sepals and petals yellowish-green striped with brown; lip white..
Oncidium astranthum, also called as Star Flowered Oncidium, Collare-stuartense astranthum, Odontoglossum astranthum, Odontoglossum loxense, is a species in the genus Oncidium. This species was described by Mark Wayne Chase and Norris H. Williams in 2008.
DESCRIPTION OF ONCIDIUM ASTRANTHUM - STAR FLOWERED ONCIDIUM
Oncidium astranthum is native to Ecuador to Peru. It is found growing in seasonally wet cloud forests of Ecuador and Peru at elevations of 2400 to 3000 meters above sea level.
It is a small sized, cold growing epiphyte or terrestrial with clustered, ovate to pear-shaped, compressed, ancipitous, rugose and longitudinally ridged with maturity pseudobulbs that are enveloped basally by several distichous, imbricating, leafless below and leaf-bearing above sheaths. The leaves are 2, apical, linear to lanceolate, obtuse, strongly keeled below, channeled along the midvein above and conduplicate to form a petiole-like base.
Star Flowered Oncidium blooms in late spring and early summer from the axillary, arching to subpendent, paniculate, with the few branches held to the apical half, to 45 cm long, 12 to many flowered, paniculate inflorescence that arise on a recently matured pseudobulb with appressed, scale-like, shorter to as long as the ovary flroral bracts. The flowers are stellate, 4 cm in diameter; sepals and petals yellowish-green striped with brown; lip white with brown-yellow markings.
ONCIDIUM ASTRANTHUM - STAR FLOWERED ONCIDIUM CARE
Cultural information should only be used as a guide, and should be to be adapted to suit you. Your physical location; where you grow your plants, how much time you have to devote to their care, and many other factors, will need to be taken into account. Only then can you decide on the cultural methods that best suit you and your plants.
Light:
Oncidium astranthum needs a light level of 15000-20000 lux for mature plants, but less for young plants and when temperatures are high (70% shade cloth over summer and more light in winter). Leaves turn reddish blue if receiving too much light and leaf loss will occur if too sun damaged. Dark green leaves indicate insufficient light. A slight bronzing of the leaves and older bulbs indicates the light is good for flowering.
Temperature:
Star Flowered Oncidium prefers cool to cold temperatures and can easily suffer from heat stress in summer. The optimum temperature range is between 8 °C and 26 °C. Night temperatures of 11 to 13 °C and day temperatures of 18 to 21 °C are ideal. Growth will be slower however if optimum temperatures are exceeded. Humidity and airflow must be kept higher as temperature increases. In their natural environment night temperatures can fall to 5°C and although tolerant of low temperatures down to 0°C, they will not tolerate frosts.
Humidity:
The plant prefers a humid environment, preferably between 40 and 80% humidity (ideal 65%). It is important to damp down the greenhouse floor or use misters to increase humidity in hot weather. Protect against hot dry wind. Pots can be placed on gravel filled trays containing water in summer to increase humidity but pots must not sit in water. Accordion pleating of leaves can be a symptom of insufficient water or humidity or irregular watering. However the pleating can also be genetic in some cases and unavoidable.
They need good air movement, particularly as humidity increases, and fans are advisable to prevent fungal diseases. Leaf fungal diseases and black spotting can be a problem for the plant.
Substrate, growing media and repotting:
Oncidium astranthum grow as epiphytes or terrestrials in the natural environment. Having finer roots they should be grown in small bark (5-10mm) perlite potting mix (5:1) or in sphagnum moss and perlite (70:30). Some growers place a layer of sphagnum moss on the top of the pot to reduce evaporation and keep the roots cool. They can also be grown in perlite with a layer of gravel on the top.
The plant should be repotted every year to every 2 years in spring or autumn when new growths are about half mature. They should be grown in small squat pots that allow more frequent watering. The base of the new growth should be planted about 1.5cm into the bark but no deeper. Keep bark barely moist until new roots appear then resume normal watering.
Watering:
Star Flowered Oncidium like abundant water and require frequent watering in warmer months. They must never be allowed to dry out. During summer irrigation will be required every 2 -3 days, however during winter rates may drop to once every 10 – 14 days. Try to water in the mornings and not in the heat of the day or late afternoon as leaves may stay wet during the evening.
They are very sensitive to poor water quality which will inhibit root growth and cause leaf-tip burn. Pots should just begin to dry before watering. Misting daily in very hot weather is recommended. To reduce leaf spotting, avoid watering in the heat of the day or late afternoon in warmer months. Also avoid wetting the leaves and water the pot, not the leaves.
Fertilizer:
Oncidium astranthum require frequent application of 20-20-20 fertilizer diluted to one-quarter to onehalf of the recommended strength all year round but less in winter. Apply fertilizer every 2 weeks when growing actively but monthly when less active. Periodically, collect rain water and use it to rinse fertilizer salts that accumulate in the mix. They are not gross feeders and too much fertilizer will harm their roots and turn leaf tips brown. Use of high phosphorus or potassium fertilizers as plants approach flowering can increase flower count and substance.
Rest period:
Star Flowered Oncidium do not a rest period to stimulate flowering nor in winter. But they need less water in the winter, especially if they grow under the conditions of a dark, short day that occurs in moderate latitudes. You can let the plants dry between the next watering, but you must not let the plants stay dry for a long time. Fertilization should be limited or should be completely abandoned until spring, when stronger watering resumes.
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