Oncidium altissimum, a native orchid with very long inflorescences and small yellow flowersl

Around the base of the lip there are some sharp pointed protuberances that form two groups of five
 around a central "tooth" 

A slightly different colored flower, however the flash and a degree of back lighting accentuate the difference with the flower on the top photo

The inflorescence is branched among most of its lenght, but the tip has two rows of flowers

A plant blooming in the wild, notice the many old inflorescences

This bottom view of a wild plant shows the root basket

These plants were attached to the trunk of a large Teak tree.  They bloomed riotously but due to the flaky nature of the bark of the teak tree they eventually lost their grip and fell.  Note the many old inflorescences.

Oncidium altissimum is an orchid whose geographical distribution includes Puerto Rico and the lesser Antilles.  In favorable habitats its relatively common and sometimes large specimen plants can be found growing on the trunks of tall trees.  I have seen this plant in the forests of the Northern part of Puerto Rico and into the mountainous interior of the Island.   When I started learning about orchids there were few orchid books that covered the orchids of Puerto Rico, the ones that were available were taxonomic treatises that were difficult to digest due to the obscure taxonomic terms and my own lack of familiarity with the characteristics of the orchids.  For years I didn’t know if the yellow flowered Oncidium that I saw in the forest was Onc. altissimun, Onc. wydleri or Onc. baueri.    Eventually this question was settled and with the books on orchids of Puerto Rico authored by Ackermann learning about the local orchid became much easier.

 This orchid is remarkably indiscriminate about its growing substrate.  I have seen it growing on rocks, on the leaf litter of a gravelly slope, on small understory trees and on the top branches of the largest forest trees.  There is however one thing that this species doesn’t tolerate and that is deep shade.  I recall finding a plant in 1999 in the Rio Abajo forest that was blooming gloriously and growing with great vigor because hurricane Georges had opened the canopy over its growing spot and it was getting lots of sunshine.  But as the forest canopy healed and the amount of light began to diminish the plant started weakening and dying.  Now in 2011 what remain of the huge plant are a few small scattered pseudobulbs that are bidding their time until the canopy opens again.

Unlike most Puerto Rican orchids Onc. antissimun makes itself quite a home in captivity and will thrive as long as a few precautions are taken that are generally the same as one would use with any other epiphytic orchid.  This orchid is intolerant of decayed, anoxic, tightly packed media, it needs an airy mix and under my care has accepted a wide variety of growing media such as coconut, bark and stones.   When the new growth has achieved a few inches in height the plant will start producing many slender roots that will grip the media and literally engulf it in a mass of roots.  This tendency to produce a plethora of roots results in the wild in the formation of a root basket that surrounds the trunk or branch of the tree that hosts the orchid.  Sometimes these roots baskets can become large, but this can spell the doom of the plant, as the new pseudobulbs become separated from the trunk and more attached to the root basket the new roots may not reach all the way to the trunk.  The result is that if the part of the root basket that is in contact with the trunk decays a portion, or most of the orchid might fall from the tree to the forest floor.   It is not rare, if a storm hits Puerto Rico during the hurricane season, to find pieces of this orchid in the forest floor along with branches and other debris.

I no longer grow this plant because it would be like going to the bother of having a refrigerator in Antartica.  They are everywhere in Rio Abajo and many plants can be seen growing in the trees that surround my house.  You can also see this orchid in the gardens of local people where they grow quite well.   One of the most distinctive characteristics of this orchid is the length of its inflorescences, they can reach a length of ten feet although most are shorter than this.  A mature plant often has many old inflorescences in various stages of decay hanging from it.  The pseudobulbs can reach six inches tall in the largest and most vigorous specimens.

This plant is rarely seen in orchid shows, it makes its appearance mainly when someone makes a educative exhibition that features native orchids.  This orchid was relatively common in orchid collection in previous decades but it has been totally superseded in the local orchid grower tastes by new hybrids that feature much larger flowers with shorter and denser displays of flowers.  As far as I know it is not subjected to systematic collection in the wild although it is not rare for visitors to the forest to carry home plants found fallen in the forest floor, but his doesn’t seem to make a dent in the wild populations.

I have an interesting anecdote about this orchid.  When I was in college I visited the home of a fellow student that lived in the metropolitan area.  His mother was proud of her plant collection and we spent some time in the garden talking about her plants.  As we walked through the garden she pointed to me an orchid and declared it her greatest disappointment, in spite of much fussing and devoted care the plant had never produced a single flower.  The said plant was an Onc. altissimum specimen about two feet across with dozens of large pseudobulbs.  Mystified by her assertion I examined the plant and to my surprise found the remains of inflorescences in practically every bulb.  Nevertheless, she insisted the plant had never bloomed.  Baffled I asked her if she had noticed the inflorescences, she answered that yes, she had waged a continuous battle against the vines that kept invading the pot of her precious orchid.  She thought the inflorescences were the expression of an invading weedy vine!  No wonder she had never seen a flower!  I educated her about the plant and next year she enjoyed a massive blooming showfrom her plant as many years of frustration was poured on an exceptional flower display.

The plants in Rio Abajo bloom in the early summer around June.  In spite of the many plants that bloom together seed capsules are not common and I have yet to find one in the many wild plants I have found in the wild.  It is said that these plant are pollinated by bees but I have yet to see any bee visit or even hang around the flowers.  The proposed method for pollination for these orchids is called pseudoantagonism.  The proposed mechanism for pollination is that when aggressive territorial bees see the flowers, they attack the flowers head on, taking them for territorial rivals.  In the process of this attacks the pollinia of the flowers is transferred from flower to flower.