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.

THE SPECIES


Onc. cebolleta. Williams 7 notes that this is one of the oldest known oncidiums, having been described as far back as 1800, although The Dictionary of Gardening 6 indicates that it was introduced into European cultivation in 1824. This plant appears under a number of synonyms: brachyphyllum, cepula, glaziovii, humboldii, juncifolium, longifolium, ottonis, sprucei and ultrajectinum.2 An interesting confusion has occurred regarding the plants grown under the cebolleta synonym ottonis. Two entirely different plants bear this name. This name has been wrongly attached to a species from another section of the genus, concolor, (of the Section Concoloria). This has the more typical leaves and pseudobulbs and is easily distinguished from the "true" ottonis by this plant's terete leaves, 22 It is understood both plants have been registered in Sanders Lists' 10 as ottonis. 21


Hawkes 1 description of this species states it has a stout rhizome, with very small roundish, scarcely noticeable pseudobulbs. The leaf is generally solitary per pseudobulb, somewhat cylindric to almost terete, elongate, tapering to sharp, often elongate point, grooved on the face, frequently more or less reddish, or sometimes red spotted, 150 to 600 mm long, often very robust, rigidly erect to sharply pendulous. The inflorescence is erect, rather stout to 750 mm long, few to many flowered, branched or not, the rachis usually reddish spotted. The flowers are variable in all parts, in the finest forms to 35 mm long, usually much smaller, the smallish undulate sepals and petals yellow, spotted more or less densely with reddish-brown, often somewhat incurving over the column. The lip is large for the flower, canary yellow to rich golden-yellow. It is shown as native of Mexico and the West Indies to Paraguay. With a quite wide geographic distribution, it is indicated 7 as being very variable, which appears to be confirmed by the number of forms listed as synonyms of this species. For registrationl8 purposes, cebolleta, sprucei and ottonis are separately retained, notwithstanding that most authorities now include all under the synonym cebolleta. 2

Oncidium cebolleta

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



Oncidium stipitatum flower and clsoe up

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.

Oncidium jonesianum

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.

 

CULTURE

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.


Onc. cebolleta grows on dry rocky hills and ridges.23 Horich 9 notes the species of this Section are epiphytes of the hot savannas and semi-arid deserts. He also indicates that these plants are "almost cactus-like in their individual construction". His comparison with cacti and succulents must surely be contrary to the simple view of orchids, but if you compare the two families, certain similarities can be seen in some of the plants, especially those which are growing under similar environmental conditions. With reference to some of the members of the Cebolletae he notes24 "if you keep these orchids humid, they will rot. Give them full sun, keep them; dry and they will love it". To survive these quite hard conditions, certain modifications to the structure and metabolism of these plants have occurred. It will be apparent that a wide open thin leaf has a greater surface area, and that under hot conditions would allow a loss of moisture through transpiration. To reduce this and to lower the surface area, the leaves have become rolled into their terete form. In addition, the outer layer of the leaves have become covered by a hard heavy layer of cutin which helps retain moisture. Also the comparative fleshiness partially arises from water storage cells within the leaf to enable survival when rainfall is sporadic. Those generally somewhat soft fleshy leaves of the Cebolletae have developed where rainfall and temperatures are seasonal and sun and heat are considerably more direct than in the shady moist forests which are generally envisaged as the homes of most orchids.22

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