Sunday, September 14, 2014

Tolumnia variegata, observations on a plant growing "in situ" on the Rio Abajo forest

As I walk through the forest I often see orchid plants growing in the trees.  Most of them are in predictable places where one would expect an orchid plant to survive and thrive.  But sometimes our expectations turn out to be wrong.  When I have found Tolumnia variegata growing in the Rio Abajo forest it has usually been growing in twigs under the shelter of the canopy.   But last week I found a group of plants growing in a leafless branch of an orange tree.  Far from been protected by a leafy canopy this group of plants is exposed to the worst of the tropical sun for most of the day.  From the orientation of the plant I surmise that the original plant germinated and grew in the underside of the branch.  But all the leafy growths are now on top of the branch, fully exposed to the sun
The leaf fans are flat and are so oriented that at midday only the very narrow top of the leaf is exposed to the sun.  This orchid has a large network of roots that runs for many inches around it in the branch where it is perched.  The leaf fans are comparatively puny compared with other Tolumnia I have seen in the forest and are definitely stunted.  The inflorescences are small and have fewer flowers than plants that grow in more sheltered spots.  However the plant looks pretty healthy and it has several inflorescences on the way.
The plant is growing fifteen feet up in a tree.  I plan to monitor its growth and blooming over the next year.  I am particularly curious to see how this plant fares in such an exposed location during the dry season when a whole month can pass without any rain and humidity can be very low for our location. 

On occasion I have brought Tolumnia plants that have fallen from the trees to my shadehouse which is not far from where this tree is located.  All have eventually died.  I wonder why a plant that lives several years on the local trees around my house perishes when moved to my garden.  Perhaps observing this plant will illuminate this question.

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