The Oncidium Section SYNSEPALA - VARICOSA


Only two species of this Section are commonly cultivated. Others included in this Section will be briefly discussed, although most are rarely found in contemporary collections

This Section was established on the type species vancosum 40 in 1889 2 and is sometimes referred to as the Vancosa.4, 2 In addition to varicosum, the other widely cultivated species of this Section is flexuosum. These two species are generally free flowering, producing long lasting colourful displays. For these reasons they are well worth including in every general collection of orchids.

Garay and Stacy 2 differentiate this Section of oncidium by the plants having conspicuous leaf bearing pseudobulbs. The flower sepals and petals are somewhat inconspicuous, noticeably clawed or constricted at their base. The lateral sepals are more or less joined, and are shorter than the lip. The disc of the lip has an uneven number of tubercules (small more or less conical protuberances or projections). The rostellum is short.

THE SPECIES

Onc. varicosum has clustered pseudobulbs, oval-oblong, compressed, furrowed with age, often rather yellowish-green, about 75 to 125 mm long. There are two, rarely three, leaves, each some 150 to 225 mm long. The inflorescence is usually nodding, the flower stalk has a bloom (glaucous), 1,000 to 1,500 mm long, able to sway easily in any air movement, branching beyond the middle, usually densely very many flowered. The individual flowers are quite variable in size, in the typical form seldom more than 35 mm in diameter. The sepals and petals are small and inconspicuous, dull yellow, barred with pale red-brown, the dorsal sepal oval, concave, the lateral sepals joined to beyond the mid lobe, crisped marginally. The most attractive feature, however, is the very large, vivid yellow lip, which sometimes has a red-brown blotch in front of the crest. Generally autumn-winter flowering, it is native of Brazil1


The variety rogersii has larger, more profusely branched panicles of very large flowers, the lip of which measures more than 50 mm across.1

Moir40 believes that many of the plants labelled "var rogersii" in fact are not this variety. He also believes many of the recently available forms of this variety in breeding have resulted in very variable progeny, and a certain amount of infertility occurs. This is suggested to arise because they have been out of their natural habitats too long, and have been inbred for a considerable number of generations. He comments that for the best breeding, and to ensure they are the most adaptable to varying cultural conditions, plants that have been obtained from their natural habitat are generally the best. The infertility suggested could also arise through their possible polyploidy.

The Dictionary of Gardening6 mentions that these plants are generally strong growing, and were first introduced into European cultivation in 1848.

Onc. flexuosum is a popular species, generally easily grown. It is regarded as a small member of the "dancing doll' oncidiums.

Hawkes1 describes a robust ascending rhizome, clothed with overlapping brownish scales, producing pseudobulbs often at rather distant intervals, most forms rooting very profusely under correct cultural conditions. The pseudobulbs are usually 25 to 50 mm apart on the rhizome, mostly oval—oblong, often yellowish green in colour, compressed, some 35 to 75 mm long. There are usually two, but sometimes only one, leaves, 100 to 225 mm long. There is usually more than one inflorescence per mature growth, to one metre long, usually dull purple in colouration, densely and extensively branched towards the apex, the individual branches wiry and mostly many flowered. The individual flowers vary in size from 40 to 60 mm long, vivid golden-yellow, usually with a red-brown blotch at the base of each segment. The sepals and petals are similar, tiny, the lateral sepals joined and divided into two equal lobes at their apex. Mostly autumn—winter flowering, it is native of Brazil, Paraguay and Uruguay.

Oncidium flexuosum flower

Oncidium ((Saltamyre X Nona) X varicosum)

Williams7 states that this plant is invaluable for cutting purposes and that the flowers last for several weeks. The Dictionary of Gardening6 lists two varieties, 'Majus' having larger flowers than the type, and 'unicolor' with clear yellow flowers.

This species was introduced into European cultivation in 1818.6

Pabst and Dungs in Orchidaceae Brazilensis note that this species is a true 'air plant' living high in trees on the ends of thin branches with little contact between the roots and the branches, in such a situation where air and the mist are the principle sources of nourishment. It is for this reason that this species quickly grows out of a pot or away from a block mount. Interestingly, this species can grow and flower successfully without being put on a mount, just hanging on a piece of wire in a glasshouse.

OTHER SPECIES

Garay and Stacy2 include the following 24 species in this Section, in .addition to varicosum and flexuosum: barbanceniae, beyrodtianum, bicolour, bifolium, blanchetii, brunnipetalum, chrysothyrsus, edmundoi, fuscans, fuscopetalum, hydrophilum, isopterum, maculosum, mandonii, martianum, megalopterum, paranapiacabense, pirarense, ramosum, spilopterum, viperinum, warmingii, welteri, and williamsii

Oncidium viperinum
My thanks to photographer/grower "Dan" USA

Moir40 includes montanum (synonym pirarense2 and cristatum (included in the Section Rostrata by Garay and Stacy.23 An article by Fowlie45 records a number of additional species.

Onc. spilopterum is seen in a number of collections and in some hybrids. Fowlie45 notes this species grows in full sun, with its pseudobulbs and roots in the muck of a swamp, its erect, long flower scapes necessary to lift the flowers above the ground.

Oncidium (crispum X spilopterum)
A modern intersectional hybrid

Williams' description9 of this plant states it has flowers 25 mm across, petals and sepals comparatively small, undulate, yellow or greenish-yellow, barred chocolate-brown. The lip is free, spreading, bright yellow with purple spots. The peduncle is some 600-1,200 mm high, branched in their upper portions. These plants are endemic to Brazil.6, 7

Onc. pirarense2 (martianum)40 has flowers 45 mm across, the sepals and petals bright yellow with brown bars, the lip is very large and deep yellow on the upper side, almost white underneath, on a panicle 450 to 1,000 mm lonI. Autumn flowering and is again a Brazilian species.6

Onc. bicolor has small sepals and petals, greenish-yellow, spotted and barred with red, lip bright yellow, broadly expanded, margin with a deep yellow depression. Flowers form a panicle 600 to 1,000 mm long, which appears in the autumn. This is a native of Brazil.6 It is indicated 6 as being a synonym of martianum, although Garay and Stacy2 retain its separate identity.

Onc. bifolium has a loose inflorescence with 5 to 10 flowers, rising to some 300 mm. Flowers are about 40 mm long, the sepals and petals yellow with some more or less dense red-brown spots. The lip is vivid golden-yellow, the lateral lobes triangular, the mid lobe somewhat kidney-shaped, deeply notched apically. Summer flowering, it comes from South Brazil and Uruguay.l

Onc. viperinum has flowers 25 mm across, the sepals and petals pale reddish-brown, barred light yellow, undulate, the lateral sepals free. The lip is canary yellow. There is a curious crest which resembles a viper's head in profile, hence the name. The flower stalk is erect, branched, 125 to 175 mm long, few flowered. A native of Uruguay.6

Moir's article 40 includes colour photographs of three species (montanum, blanchetii, and flexuosum), as well as some of the intergeneric hybrids utilising species of this Section.

BREEDING

Moir40 reports that up to 1975, only three hybrids between species of this Section have been made, these being Java (varicosum x flexuosum), Kanoa (Java x varicosum), and Waiomao Gold (montanum x varicosum). 26 Most of the other large lipped oncidium hybrids are mixtures of varicosum with members of the Crispa group. Crosses with the Crispa species add large brown tepals to the flowers where practically none existed in the Synsepala species.40

The species varicosum has been the most widely utilised in breeding. The earliest introduced rogersii forms were determined to be tetraploids and polyploids.40 and herein lies the probable reason for their breeding value. This species imparted valuable qualities to the hybrids, a large skirted lip, long lasting flowers, and an ability to maintain flower quality even when the pollen is removed. A disadvantage is a tendency to grow away from the media as if wanting air between them and the media. The introduction of Crispa section species brought in brown spots on the flowers and may have also made the hybrids easier to grow.40 Varicosum is noted 8 as being always dominant in breeding.

Oncidium varicosum

Certain intergeneric crosses have been attempted. With brassia the growth and damper culture required for brassias does not mix with the "no wet feet" and dormancy of varicosum. Varicosum has also imparted magnificent qualities to miltonidiums, colmanaras, beallaras, and alicearas, all having the beautiful large skirt of varicosum with other shapes, colours, multiple branching and a "very lovely display.40

One interesting feature of hybrids from this section is the registration26 of Nona For reasons known only to the Registrar, two different hybrids bear this name. The first, crispum x varicosum is an equal blend of each species, the other Nona 'II' is 7/8 varicosum and 1/8 forbesii. While subsequently corrected, hybrids incorporating Nona as a parent could include either form. This may have arisen because of the uncertain taxonomy regarding the species validity which existed involving the Crispa oncidiums at around the time registration was completed.

CULTURE

Moir,40 ex Orenstein, advises varicosum "should be dried off when the flowers begin to fade, and for three to four months thereafter. By dry I mean apply water only to prevent severe shrivelling. The plants will look bad after a few months, but they bounce back 100% when growth commences, usually in 'September and October'.* The other thing is mature plants and seedlings need very bright light for growth. They grow poorly and die in cattleya conditions, but grow like weeds when given lots of light. The plants will benefit from heavy fertilisers when in growth."

*In Southern Hemisphere.

The Dictionary of Gardening 6 indicates most species are cool to cool—intermediate growing. Hawkes 1 states higher temperatures are required, intermediate to hot conditions.

Williams,7 for bifolium, recommends pot culture, this suspended from the roof of the glasshouse, and suggests the inclusion of sphagnum moss, although emphasises ample drainage must ALWAYS be given, especially as the plant enjoys a liberal supply of water when in active growth. For flexuosum he advises warm house culture, for varicosum, the cattleya house. Actual temperatures unfortunately are not specified, although the various authors’ general recommendations are indicated. It appears minimum night temperatures of 13 - 15 oC are suggested. With the dry winter dormancy, lower winter temperatures are suitable, with higher minimum night temperatures during periods of active growth.

Local growers have found that the maintenance of high levels of humidity, especially during the period of active growth, is necessary for flexuosum. Most success locally appears to be with plants mounted on slabs of treefern (especially on Dicksonia fibrosa if it can be obtained). Good culture often indicated by the extensive mass of active roots which are produced, especially for flexuosum.

Within this Section is a group of species described as uliginous (growing in wet or swampy places) by Fowlie.45. The species he includes grow amongst leaf humus with a plentiful supply of moisture in rocky places, or in swamps themselves, protected from the seasonal fires which frequently sweep the habitat. The names of two species hydrophylum (friend of water) and uliginosum (oncidium of the swamp) are descriptive of the habitat. For fuscans, Fowlie notes this habit is a windy one where regions without this air current but with the same rocky habitat did not contain these plants. Fowlie45 describes the following groupings with specific habitat details. This information may assist in the culture of this group of plants.

(a) Growth in full sun; roots in niches and crevices with pseudobulbs exposed on bare rock or appressed under small boulders; no shade trees nearby; highly endemic to 50 square mile areas. Pseudobulbs thumbnail sized.

Onc. fuscans. On exposed, decomposed rocky granite outcrops near windy summits (Brazilian-Rocoas) Serra Caracol.

One. gracile (Concoloria Section2).On exposed rocky summits of Central Minas Gers is always with rupicolous laelia species. High ridges where the specific heat of the promontory is low (being iron ore) and hence serves to nightly condensate moisture from passing clouds.

Onc. montanum. Not yet re-found but according to the original description on stony outcrops of unusable land amongst grasses on the Serra das Pocas.

(b) Growing in full sun; pseudobulbs and roots buried down into muck of swamp making presence known only at flowering time with erect foot-long scapes which carry flowers above the grasses. Inhabit high swampy areas at 1,400-1,675 metres elevation. Pseudobulbs up to an inch in diameter:

One. spilopterum. Autumn flowering. Endemic to only the high swampy lands of the Serro do Cipo in Central Minas. No known close relatives.

One. hydrophilum. Large flowered species from swamps of Planalto of Brazil. Blooms in spring time.

One. uliginosum (listed as barbaneniae2). Lost species of swamps near Pocas da Caldas.

One. ealdense (sym. ramosum2). Refound species growing on grassy swamps of bauxite summits near Pocas da Caldas. Flowers in autumn.

One. barbaeeniae. A newly described species.

One. cipoensis. Flowers in springtime. Grows with spilopterum in same habitat and indistinguishable when not in flower. However, blooms in six-month opposite season.

(c) Growth in partial shade, roots in deep humus mats kept moist by shade and situation between boulders; prefers rocky promontories with gnarled vestigial forest trees or gullies amongst large boulders and humus. Distribution 200 square mile areas. Pseudobulbs 75 mm in diameter with 450 mm leaves.

Onc. paranapiacabense. Amongst boulders in leaf mats near promontories with a few vestigal shading gnarled forest trees. Western Minas into Parana.

Onc. blanchetii. On rocky slopes with humus mats and close to trickling water. Frequently with different Zygopetalum species, often with stunted forest nearby. Central to eastern Minas Gerais.

Onc. ramosum. Prefers moist gulches or pedreiras amongst sandstone boulders, especially near permanent rivulets. North eastern Minas near Diamantina.

These plants are natives of the foothill mountain habit subjected to the summer monsoon. These habitat notes can be usefully referred to for further information..

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