The Oncidium Section PLURITUBERCULATA / MILTONIASTRUM

The 'mule eared' oncidiums

The Cebolletae Section is a group of plants adapted to relatively hot dry situations. Now we consider plants which are adapted to even more extreme environments where often very hot and dry conditions are experienced. Species in this Section, which was established by Lindley in 1850, are known by the name Plurituberculata, this name coming from the conical protuberances on the crest of the lip. In 1852 Reichenbach f. applied the name Miltoniastrum to this Section and hence this name is also widely used, although the first appears correct as it predates the second. These plants are commonly known as the "mule" or the "burro" eared oncidiums, in deference to the shape and attitude of their Many of these plants themselves are attractive, and when in flower put on a spectacular display, in the main producing quite long lasting flowers.


Garay and Stacy
2 distinguish plants in this Section by their more or less fleshy sepals. The petals and lip are membranaceous, with the exception of the callus. The pseudobulbs are small, bearing a prominent terminal leaf, enclosed by a non leaf bearing bract at its base. The leaves are flat, or with two parts folded together lengthwise, and are of a heavy flat leathery texture. The crest of the lip is hairless and covered by small more or less conical protuberances.

THE SPECIES


Onc. altissimum is also known by the names boydii, cuneatum, forkelii and guttatum, with altissimum being the correct name of the commonly known as luridum. 2 Hawkes,1 under name luridum, describes this plant as essentially lacking pseudobulbs, borne from a robust rhizome. The leaves are variable in size, rigidly leathery, often with some dull brown or reddish-brown, loosely or densely paniculate, the individual branches usually short, 3 to 5 flowered. Individual flowers are 25 to 25 mm in diameter, extremely variable in colour, usually yellowish brown or red brown, with some yellow irregular, or regular, markings or spots. The sepals and petals are clawed, very undulate marginally, the dorsal sepal broadly oval to almost roundish, concave, the lateral sepals free, spoon shaped, the petals oblong. The lip is 3 lobed, the lateral lobes small and rounded with its margin rolled back, the mid-lobe short and broadly clawed. This is mostly spring to autumn flowering, and is native of South Florida, West Indies, Mexico to British Guiana and Peru. Williams7 states the flowers are freely produced, and notes two varieties 'dodgsoni' and 'guttatum' with distinctive flowers. The Dictionary of Gardening 6 identifies further varieties, intermedium, morrenii, purpuratum, and roseum. This species was introduced into European cultivation in 1822 .6
During the 1970's there have been published 2,41,42 a number of articles which have raised questions regarding the correct name for the plant which has been widely known for many years as Oncidium luridum. It was first illustrated by H. Slone in his 1707 publication Hist. Jamaica as Epidendrum altissimum. This illustration was of the floral parts, with a very brief description of the vegetative portions.

In 1755, an Austrian explorer and plant collector by the name of N.J. Jacquin left Europe and after travelling through the West Indies, returned to Vienna in 1759. In 1760 Jacquin published a short report on the discoveries, including a description of the plant we know as Oncidium luridum, but again as altissimum, although he placed it in the genus Epidendrum as was the convention at that time for all epiphytic orchids. Jacquin cites at this time the earlier Slone illustration. In 1763, Jacquin published an expanded report of his travels, and there illustrated and described altissimum again. Unfortunately, while only three years had elapsed since the original description, this illustration and description was of a completely different plant, although also given the name altissimum. The actual descriptions of the two plants were also quite different. It appears from other reports that Jacquin made this same mistake on a number of other occasions. The second plant he named altissimum in 1763 has been the plant generally considered to have this name since then, the first plant as described in 1760 remaining unnamed until it was again described by Lindley in his Botanical Register of 1823, and there given the name Oncidium luridum. This name situation was accepted until 1972.


Garay believed that the first 1760 description by Jacquin was based on the original Slone illustration
of 1707. The Slone material still exists in the British Museum, and bears the name "Epidendrum"altissimum, and is clearly identifiable as the commonly known luridum, and additionally, is distinctly different from the plant described three years later in 1763. He believes that because the 1760 plant is clearly identifiable as being '?uridum", and as it predates the publication of the description of the second plant of 1763, that this first plant must take the name "altissimum". Such a change means that the name of the second species is invalid, and also requires amendment.


With respect to the second species of oncidium the accurate identification of this was necessary. The originally published 1763 illustration by Jacquin only showed part of the plant, and it appeared to be the species
wydleri, of the Planifolia Section of the genus. The actual specimen Jacquin described plus the full size life size illustration which had been published only in part in 1763 has been since discovered by Garay, this revealing that this plant was actually is from the Planilabria Section of the genus, as delineated by Garay and Stacy 2 . Jacquin stated that the plant was collected in Martinique, but since then Garay reports no second specimen has been discovered , either in the entire chain of the islands of the Lesser Antilles (where Martinique is located) or anywhere else in the American tropics. He therefore suggests that’s Jacquin’s specimen is an undescribed species, which he proposes to call Oncidium jacquinianuym. Garay has also suggested that perhaps the "Jacquin material may be actually of South American origin, probably from Colombia, and that the specimens referrable to it have most likely been confused with Planilabria, another uncommon species".


The plant we have called
Oncidium luridum for so many years seems to have been in our collections, with the wrong name. It therefore appears necessary for us to amend our labels to the correct one of Oncidium altissimum (Jacq.) Sw to give it its full citation. As it has, however, been known for so long as ‘luridum’ and registered in the Sanders Lists10 under this name, luridum is likely to be maintained in common usuage for some time, notwithstanding that this name appears botanically invalid, and cannot be attached to any currently described species.


Not all botanists agree with these name changes of Garay and Sweet. While their arguments appear logical and consistent, both names will be seen in various books and articles. If you have a plant named
Onc. altissimum that does not key out to the Plurituberculata Section, you know you have something that has been caught up in this unfortunate name game .

Onc. aurisasinorum is also known as oreja de burro in its native Honduras.14 It is recognised as one of the smaller burro eared oncidiums, with stiff leaves attached to very short pseudobulbs, light green in colour. The milky white waxy flowers are produced in a dense cluster at the end of a 450 mm stem. Each flower is 35 mm long with slender spreading sepals and petals, the dorsal sepal cupped at the top. The lip is 3-lobed, the sides of the lateral lobes folded back to make them appear triangular, while the mid lobe is anchor shaped. It is autumn flowering. 1

Oncidium (aurisasinorum X stramineum)

Onc. bicallosum is described as being similar to cavendishianum although is less robust7 and differs from the latter by having its flowers in a raceme instead of a panicle, and by larger and differently hued flowers with smaller lateral lobes.1 Pseudobulbs are essentially absent, borne from a robust rhizome. Leaves I—2, very heavily leathery, rigid, usually yellowish, mostly strongly V shaped, keeled at the back. M6stly loosely many flowered the flowers are often more than 50 mm long, yellow to golden-yellow, often flushed with brownish green, the lip bright canaryyellow, the callus white dotted with red. The sepals and petals are similar with undulate margins, the dorsal sepal concave, almost hooded, the laterals narrower. The lip is three lobed. Flowering is in autumn and winter, and it is native of Mexico Guatemala and El Salvador.' It was introduced into European cultivation in 1842. There are two forms noted, 'aureum' (yellow) and 'Sanderae' (an improved form).6 It is said to make a fine winter flowering specimen, continuing in perfection for a long time. 9

Onc. carthagenense, a huge member of this group.14 Pseudobulbs are almost absent. The plant has a solitary leaf, rigidly fleshy, usually more or less spotted with brown or maroon 150 - 600 mm long, 30 - 7S mm wide, keeled towards the base. The inflorescence is erect or arching, many flowered, usually branched, to 1.5 metres tall. Flowers are highly variable in size and colour, averaging 20 mm in diameter, usually more or less heavily blotched and spotted with purplish rose on white.1 Widespread from Mexico through West Indies to Venezuela, Brazil and Colombia, it is summer flowering. 14

Introduced into cultivation in 1791 being one of the very earliest described Oncidiums. It is noted as being a widely distributed and variable species, with varieties 'roseum' (suffused rose), 'sanguineum' (smaller, pale yellow with irregular bright crimson spots) and 'Swartzi' {whitish, variegated red, brown and purple. 5 Synonyms are henchmannii, huntianum, kymatoides, obsoletum and oerstedii, roseum, salvadorence, sanguineum and undulatum. 1 The number of synonyms indicates the natural variability of this species.

Onc. cavendishianum is also known as pachyphyllum and panduffferum 2 and has I—2 leaves, borne from a very robust rhizome, very leathery, usually yellow-green, to 600 mm long and 200 mm wide. The inflorescence is stout, erect, to I metre tall, usually a many flowered panicle. The individual flowers are waxy, fragrant, about 3S mm in diameter, the undulating sepals and petals sometimes entirely yellow, more commonly greenish-yellow, more or less densely spotted and blotched with red.

The lip is bright yellow.1 The crest of the lip has protuberances in the form of a cross 4. Native of Mexico and Guatemala. It is winter to early spring flowering.1 Williams states this is a very showy and noble species with a bold and striking habit.7 It has been in European cultivation since 183S.6

Onc. chrysops is closely allied to bicallosum, 6, 7 having light brown sepals, broader light brown petals which are somewhat wavy, lip bright yellow. It has been cultivated since 1888.6

Onc. haematochilum is a compact growing and handsome plant,7 which is listed as being a natural hybrid between lanceanum and luridum (altissimum). 1,6 Its inflorescence is more than 600 mm tall, erect or arching, paniculate, many flowered.

Flowers are 50 mm in diameter, very fragrant, long lasting, petals and sepals yellow green, heavily blotched chestnut brown.1 Winter flowering, it is noted as being a synonym of altissimum (luridum) purpuratum. 6

Onc. lanceanum is a remarkably handsome and distinct species 7 having rigidly erect, heavily leathery leaves to 550 mm long by 125 mm wide, dark dull green more or less densely spotted with purple. The inflorescence is erect, often panicled, few to many flowered, to 450 mm tall. Flowers are very waxy, long lasting, to 65. mm long, not as wide, petals and sepals yellow-green, more or less densely spotted chocolate brown. The large lip is rich magenta, sometimes whitish. Mostly summer flowering, it comes from Columbia, Venezuela, Guianas, and Trinidad.l Introduced in 1834, there is a very desirable variety with a pure white lip, the variety. lourrexianum. 6 Flowers last 4 - 5 weeks in perfection if kept free from damp.7

Oncidium lanceanum

Onc. limminghei is a species placed by some botanists in this Section of the genus, but in the Glanduligera by others,2 the later Section, however, appearing to be more appropriate. For a more detailed discussion of this matter, refer to the Glanduligera Section page. It has flowers 3—S in succession, 35 mm in diameter, golden. yellow spotted brown. Summer flowering, it is native of Venezuela.7

Onc. lindeni has fleshy leaves, about 50 mm across, flowers pale yellow, marked chocolate-brown. The lip is fiddle shaped, purplish violet, yellow around the crest. Native of Mexico, it has been in cultivation since 1869.6 This plant is also known as retemeyeranum,2 and has the distinct characteristic for oncidiums of the flowers opening in succession.16

Onc. lowii is suggested to be a natural hybrid between carthagenene and cavendishianum, having many flowers in a tall paniculate scape. Petals and sepals are undulate, spotted red-brown, lip yellow spotted red-brown at its base.6

Onc. nanum has many 20 mm wide flowers, with yellow sepals and petals, which are spotted brown. The lip is bright yellow. It has an erect, panicled scape, with branches closely set. Native of Guiana and north west Brazil and east Peru, it was introduced to European glasshouses in 1852,6 It flowers in summer.


Onc. pumilum has small yellow numerous flowers on a short upright panicle. Summer flowering with leaves 50 to 125 mm high, it is native of Brazil, and has been cultivated since 1824.6

Onc splendidum has clustered oval to almost round pseudobulbs, more or less compressed, usually dull brownish green, 35 to 50 mm tall. Its leaf is solitary, usually coloured like the pseudobulbs, rigid, very heavy and thick, keeled behind, to 300 mm long and 75 mm broad. The inflorescence is stout, erect, to 1.2 metres tall, few to many flowered. Flowers are to 75 mm long, long lasting, very handsome, the sepals and petals similar, bright yellow, heavily blotched and spotted rich brown or reddish-brown, undulate, rather reflexed at the tip. The lip is very large, vivid golden yellow, almost flat, lateral lobes small and rounded, often with an apical brownish suffusion. Mostly spring early summer flowering, this species is native of Guatemala and Honduras.' Introduced into European cultivation in 1862.6

Oncidium (aurisasinorum X stramineum)

Onc. stramineum resembles a small altissimum {luridum) 1 Its leaves are longish and narrow, very rigidly fleshy, narrowed into a stout short petiole, 150 to 200 mm long. The inflorescence is paniculate, inclined or hanging, to about 200 mm long, usually shorter, rather densely many flowered. Flowers are about 20 mm across, white or straw coloured, usually speckled with red or pinkish lilac on the lateral sepals, lip and column. Sepals and petals are widely spreading, almost round, the dorsal concave. The lip is very shortly clawed. Summer flowering, it is native of Mexico1 and is sometimes known by the synonym affetinum. 1

In addition to the species listed above, Garay and Stacy2 list echinophorum (syn. Oncidium limminghei), johnii, oestulundianum and pohlianum, although no information on these is available in the literature seen.

BREEDING


These species have been quite widely utilised in breeding, both in intra and intersectional hybridisation. The Sanders Lists of Orchid Hybrids18 indicates hybridisation started in the 1930s, with the cross splendidum x cavendishianum registered in 1931, with a steady stream of registrations since then. The breeding has extended past the primary crosses to more advanced hybrids, being one of the few Sections where this has occurred to any significant degree. The species of this Section most used in hybridisation are altissimum, splendidum, lanceanum and carthagenense with, amongst others, cavendishianum, bicallosum, aurisasinorum, stramineum and haematochilum. Intersectional hybridisation has involved many other Oncidium Sections, such as Crispa, Cebolletae, Synsepala, with some intergeneric breeding also having been completed, with brassia and trichocentrum for example, although Moir8 believes most of this breeding only produces sterile hybrids.


Breeding characteristics with the
Cebolletae were discussed in the page on the Cebolletae


CULTURE


In the page on the Cebolletae, the desert-like habitats of those species were noted. It is said that the species from the Pludtuberculata Section are able to withstand even more severe conditions. Certain physiological and metabolic adaptations distinguishing them from the usual oncidiums (and other orchids) are found. These plants in the main have very thick leathery leaves. They characteristically have a "V" shape, apparently to decrease the flat surface of the leaf area exposed to the sun. This shape also adds support to the somewhat heavy leaf. Most of the leathery leaves have a thick layer of cutin, again to reduce surface moisture loss.Stomata, through which the plant respires, are typically, or predominantly, concentrated on the lower leaf surface, often found in slight depressions, again to reduce water loss under hot conditions. The stomata also have large guard cells with small air pores, to further minimise moisture loss. Certain plants have certain cells which have been thickened, which assists preventing cell collapse should dehydration occur. Withner,22 concludes that the hard leathery leaves provide the most effective means of water retention, essential for the plants survival under the conditions where these plants are commonly found.


Because of the naturally dry conditions of the habitats of these plants, they must be allowed to dry out between waterings, especially when growth is slow, such as during the winter—a wet/dry cycle of 3 - 7 days being appropriate during the year. As noted with the
Cebolletae, growth is also best maintained when there is a diurnal temperature fluctuation to allow the night absorption of carbon dioxide, and day photosynthesis, again a modification to prevent water depletion.


To consider the specific culture, Hawkes 1 notes the Plurituberculata Section plants do well in almost full sun, and appear to flower better than when kept in shady situations. He indicates intermediate or intermediate/hot conditions should be maintained for best results. Plants must have perfect root drainage at all times, otherwise problems can occur. He also states that all oncidiums benefit from regular and liberal applications of fertiliser, although excessive fertilising can result only in lush growth with few flowers in some situations.1 Plenty of fresh moving air is also conducive to plant health, as such airy conditions are usually an essential element of the oncidiums natural habitat.

The Dictionary of Cardening 6 classifies the species listed in that publication according to general temperature reguirements; all those requiring the highest "tropical" conditions are carthagenense, haematochilum, lanceanum, limminghei, lowii, nanum; those requiring lower intermediate (Cattleya-like) conditions are altissimum, aurisasinorum, bicallosum, cavendishianum, chrysops, lindeni, pumilum, splendidum, and stramineum.

Oncidium splendidum

Williams7 notes that cavendishianum may be-grown on blocks or in a pot, in the cattleya house, but because of its size, seems to do better in the latter. For lanceanum the tropical house temperatures are confirmed, on a block or in a basket "making a splendid plant for exhibition". Altissimum (luridum) needs cattleya conditions, again with pot or basket culture.

Remember, growing orchids is all about enjoying your plants
and sharing your growing success with friends and family.

Good luck and good growing.

   
   

If you wish
you may

E-mail
me at -

powwebmaster
@ihug.co.nz
 


 


Click above graphic to see list of societies in your area.

 Site established 9th May 1998
Oncidium series first uploaded 20 October 1999