PLANT OF THE WEEK

Dr. T. Ombrello - UCC Biology Department

 

ONCIDIUM ORCHIDS

 

Common names: 

While this species does not have a common name, members of the orchid genus Oncidium are often referred to as Dancing Ladies or Dancing Dolls because the long sprays of flowers resemble groups of ballet dancers.  They are also called Butterfly Orchids because of the floral resemblance to the colorful insects and their tendency to flutter in a breeze. 

Many people wonder why orchids are usually called by their scientific names instead of common names.  The reason is simply that few have been either known or cultivated long enough to have acquired common English names.  Orchids have been important in horticulture for little more than a century, and only have become widely available in the last 50 years or so.  Forty percent of all orchids have no names whatever in their native lands, and that figure rises to about 90% when they are exported to foreign regions.  In time, many will probably be given simple common names. 

 

Scientific name:    Oncidium sphacelatum

Explanation of scientific name:

Oncidium- from the Greek for swelling or tubercle, alluding to the crest on the lip of the flower.  

sphacelatum - dead, withered, diseased.  To the Meso-American Indians, the sunny yellow flowers streaked with stripes of dark reddish-brown signified human blood reviving the sun in time of danger.  This species, along with its close relatives, has long been associated with the dead by the native peoples of Central and South America, and probably had some intimate connection with some forgotten Toltec or Mayan funeral ceremony.

Oncidium sphacelatum is one of over 750 species in the genus Oncidium, and is a member of the large Orchid family (Orchidaceae). The Oncidiums are native to the western hemisphere, and this particular species naturally ranges from Mexico to Honduras.  Oncidium sphacelatum is a prolific epiphyte.  It grows on other plants, such as in the crotches of tree limbs, but does not derive nutrition from or harm its host in any way.  The plant consists of elongated and flattened storage stems (pseudobulbs) clustered together with several leaves on each.  The roots are designed to cling to the substrate upon which the plant is growing.  The species blooms in the spring, producing long (up to 5 feet) stalks bearing many flowers.  This species displays the most prevalent flower colors found in the genus Oncidium:  yellow, spotted and barred with reddish-brown.  

Orchids have an amazing array of flower shapes and sizes and have evolved interesting mechanisms for pollination.  Some orchids ensure fertilization by means that are so bizarre as to be hardly believable.  All orchid flowers, however, have the same basic parts.  The flowers have 3 sepals and 3 petals, although some of these parts may be fused or greatly reduced in size.  One of the petals (the lip or labellum) is different in that it is often larger and showier.  Projecting from the center of the flower is the fleshy club shaped column, which is a fusion of male and female reproductive organs.  The top of the column is the male anther with its pollen grains grouped in masses called pollinia.  Below the anther is the female stigma, a sticky surface on which the pollinia are deposited during pollination.  Below the stigma is the ovary, which expands into a seed capsule (fruit) after fertilization.

Oncidium orchids are insect pollinated.  The pollinator is an aggressive bee that drives other insects from its territory.  This characteristic of the bee is taken advantage of by Oncidium orchids.  Their flowers mimic an antagonist, causing the bee to attack them.  The bee does not land on the flower, but merely strikes it, so that the pollinia become attached to its head.  The pollinia bend downward slightly after they are cemented to the front of the bee’s head, so that they press into the stigma when the bee attacks a second flower.  The bees must be accurate to within a millimeter to effect the exchange, yet rarely miss.  Oncidium flowers do not look much like insects, yet something about their color or shape causes the bee to attack.  The net result is that the Oncidium flowers are cross pollinated, ensuring a mixing of genetic information from generation to generation.