The Oncidium Section Cebolletae
This aggregation of plants stands out from the usual oncidiums by their rounded, terete leaves. Williams,7 in 1894, noted that "while not attractive plants they have never found much favour with orchid growers, and as a consequence are not frequently seen in orchid collections". With the increasing popularity of oncidiums, and in view of the distinctive characteristics of these plants they are, however, now becoming more widely grown, and when in full flower do give a quite spectacular display.
Lindley established the Section Cebolletae in his Botanical Register of 1842, on the species "epidendrum" cebolleta. Garay and Stacy 2 distinguish this Section by the more or less fleshy sepals of the flowers. The petals and the lip are membranaceous, except the callus. The pseudobulbs are small with a prominent well developed terminal leaf, enclosing a non leaf-bearing bract at the base. The leaves are terete, being more or less circular in cross section. Most are referred to as the 'rat tailed' oncidiums.
In 1997 Koeniger and Pongratz transferred these species to the new genus Stilifolium. In December 1999, Eric Christenson in Lindelyana resurrected the generic name Cohniella, based on the prior name of Reichenbach of 1825.
Northen l4 states that the name 'cebolleta' means in Spanish "small onion", in deference to the terete leaves of these plants.
Onc. teres. Hawkes l indicates this is vegetatively identical to stipitatum (described below) with its inflorescence a densely, many flowered panicle, to 450 mm long. The flowers are to about 12 to 15 mm long, the sepals and petals yellow, very heavily spotted with reddish-brown, the lip bright yellow on the frontal surface, the reverse surface and disc heavily spotted with reddish brown. Winter and spring flowering, it is native of Panama.
Onc. stipitatum (synonym lacerum2 ) has flowers distinguished from the species by the longer lip isthmus, and the much less prominent callus.18. Native of Honduras, Nicaragua, and Panama, it bears a flowers, having yellow coloured brown barred sepals and petals, with a yellow lip. It is summer flowering. l4
Onc. nudum, also known as ebrachiatum,2 and is described under this last name by Hawkes, l is another appearing vegetatively similar to stipitatum, having leaves to about 600 mm long. The inflorescence is usually solitary, arching, paniculate flowers are about 6 mm long, or more, the sepals and petals yellow spotted reddish brown, the lip yellow on both surfaces. The dorsal sepal is concave, incurving over the column, the petals widely spreading. Winter flowering, it is native of Nicaragua and Panama.
Onc jonesianum. Northen l4 states that from a plant that looks very similar to cebolleta comes the most striking and decorative 75 mm flowers, 10 to 15 per stem. The dorsal sepal and the petals arch upward, while the lateral sepals are held behind the flower; all are cream-white, very much ruffled and marked with scattered red spots. The outer lobe of the white lip is broad and spreading, divided in the middle, attached by a claw from which two bright yellow ears spread sideways and which is decorated by a complicated crest. A native of Paraguay, Brazil and Uruguay, it flowers in the autumn.l4 Williams 7 states this species has very clustered, small pseudobulbs, with flowers very elegant in character. It lasts some time in beauty. The Dictionary of Gardening 8 states that this is a beautiful variable species, introduced into European cultivation in 1883, and mentions two varieties, 'flavens' with sepals and petals yellowish-green spotted yellow, and 'phaeanthum' with sepals and petals reddish brown, and a white lip.
Onc. ascendens was introduced into cultivation in 1839.6 The flower is yellow, red near the crest, with red stains on the sepals and petals. The column wings are incurved. A native plant of Mexico and Central America, 6 this goes also under the synonym bolivianense .2
Garay and Stacy2 include three other species in this Section, ostenianum, stacyi and Wittli. The only information on these species available involves stacyi, which is considered by Moir 20,21 not to be a typical terete oncidium but probably a chance in a million natural intersectional cross between a Cyrtochilum species and jonesianum. Only recently discovered, it was named after John Stacy. A native of Bolivia, it has large yellow-brown blooms with terete leaves 1,000 to 1,300 mm long. The flowers are on 2 metre stems, with the flowers 75 mm in diameter. It is a scarce species as it grows on the huge mahogany trees which are being increasingly cut for timber, thus destroying their native habitat. Growing under dry conditions, it has only a short flowering period, and it is believed this is the reason it remained undiscovered for so long.
Sanders Listsl8 indicates these plants have been used in hybridising to a limited extent. Up to 1975 only one intra-sectional hybrid had been registered, this, in 1968 between sprucei (cebolleta) x stipitatum15 known as Spurtat. The first intersectional registrations (three) were made in 1940, with 18 years elapsing for the next (1958). Between 1964 - 1968 eight were made, and three from 1970 - 1973, a total of 14. In addition the species have been crossed with two advanced hybrids, cebolleta x Mem. Pepito de Restripo (splendidum x altissimum(luridum)) in 1971 to make Richard Saporita, and ottonis x Palmyre in 1970 to make Henry Ku. The most popular Cebolletae species is cebolleta (or its forms sprucei and ottonis), used in 9 of the 15 crosses. Species from six Oncidium Sections have been utilised, although only those from one have been widely used, these coming from the Plurituberculata Section, which accounts for 9 of the 15 crosses.
Charanosri and Kamemoto 27 have studied the hybridisation between the Cebolletae and Plurituberculata Sections. Despite differences in their chromosome numbers (diploid 2n counts of 26, 28, 30 and 36 in Plurituberculata; 30 jonesianum and 36 in Cebolletae), good cross compatibility both within and between the sections was shown, indicating a close relationship between the plants of these two sections. Some species performed differently, however, depending on whether they were the pod or pollen parent. For example lanceanum performed poorly as a female parent but well as a pollen parent. Splendidum produced good fruit set in either direction with members of the Section Plurituberculata but seed viability was poor when used as the female parent. The reverse was true when splendidum was crossed with members of the Cebolletae Section. Pollinations made within the Cebolletae Section produced fruit and viable seeds eg,ually well in both directions. However, in cross pollination with Plurituberculata, greater success was obtained when the Cebolletae species were used as pollen parents. Moir 8 states these species generally produce sterile hybrids when they are crossed with other Oncidiinae, and most other oncidiums.
One of the distinct characteristics of these plants is their terete (rounded) leaves, in contrast to the more flat open leaves usually seen in most orchids. As noted by Withner 22 "modifications . . . of leaves are related directly to the ecology of the individual plant. . . . Orchid leaf types are a direct result of modifications enabling the plant to cope with a specific microhabitat." 22 In view of the distinctive vegetative features of the plants of this Section, it is worth considering further the modifications that have taken place, as this will help clarify their particular cultural requirements.
While there are other orchids able to take even drier hotter environments (e.g. the Miltoniastrum Section Oncidiums), it will be apparent that in a glasshouse we must provide plenty of light and allow the plants to dry before watering, although not to aridity.
It will be generally understood that most plants absorb carbon dioxide from the air during the day for photosynthesis, and then the plants basically rest at night. In hot dry environments, this daytime respiration will, however, cause a loss of moisture which could be fatal to the plant.23, 25 A number of cacti and certain thick leaved tropical epiphytic orchids have developed a specific modification which enables them during the night to absorb carbon dioxide from the atmosphere, and fix it into a form for use when light is available for photosynthesis. During the daylight hours temperatures are high, bark and roots are dry and humidity is low. These plants close their stomata, and water is conserved in their tissues. At night the stomata open and the temperatureŚmoisture relationship does not induce stress. Experimentally it has been found that if these plants are not subject to day and night temperature fluctuations, the night fixation of carbon dioxide is not possible, not allowing the daylight manufacture of food, and therefore growth is affected. It has also been found that strong daylight is necessary to provide the proper precondition for the cells to store carbon dioxide at night.25 We therefore have two clues to the optimum culture of these plants; diurnal temperature variation, and plenty of sunlight.
It is emphasised by Withner25 that while maximum light is important, if this can be given without the usually associated temperatures rising to high levels the best results will be obtained. During high temperatures, plant respiration increases and greater photosynthetic activity is required just to maintain the food reserves. If these reserves are not maintained the plant will gradually deteriorate, this occurring under high temperature conditions as photosynthesis cannot keep up with the respiration taking place. Strong light at low temperature levels should therefore be the aim, not only for the Cebolletae but all plants, notwithstanding that these plants can probably tolerate higher temperatures than many other orchids. The light and temperature levels must be determined for each plant, in relation to what they experience in their natural habitats, as there is wide variation in individual requirements, although the same principles apply to all.
Most of the cultural information noted for specific species is along the lines indicated above. For stipitatum Northen4 states this plant can be grown warmer than some, in a pendant position. Cebolleta is common to warm areas throughout the American tropics, where it is equipped to endure long dry seasons. Jonesianum likes bright light and not too much water. For these plants, a wet/dry cycle of watering of 2/3 days will generally be appropriate.
Hawkes1 states that the plants of this Section should be grown on slabs of tree-fern fibre, or on rafts, hung vertically. For all his listed species, intermediate to warm temperatures are indicated. Other relevant features mentioned are high light intensities, and the provision of very free drainage to the roots of the plants. The Dictionary of Gardening 6 states these plants should be grown in the intermediate house with cattleyas throughout the year. Williams 7 also confirms intermediate house culture is applicable.
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Site established 9th May 1998
Oncidium series first uploaded 20 October 1999