Tuesday, January 4, 2011

Ponthieva ventricosa, the smooth shadow witch, a Caribbean endemic

Ponthieva ventricosa, in situ
Side view of the flower in its natural position

The pollinia (yellow masses) joined by  the stipe which end in a vicid disk (grey) that will attach to the insect,  The column is  just behind the pollinia and you can see the opening of the gynandrum.
A flower against a black background

The lip showing green stripes, in this flower the pollinia can be seen in top view

Ponthieva ventricosa is a small orchid that is endemic of the Greater Antilles.  Its distribution is apparently confined to the “mogotes” region of Puerto Rico.  A few years ago I found a small colony growing in a bank of a road.  This orchid blooms from December to February but for some unknown reason only a few of the plants bloom.  Almost all the plants show some degree of damage on their leaves but it is unclear what is causing the damage.  All the plants I have found have been growing on the side of nearly vertical surfaces along with a few ferns.  I wondered why these orchids were not displaced from their site by more aggressively growing plants but I think I got the answer during the dry season.
At one point in the dry season the bank was nearly bone dry and even the orchids which have underground water storage organs withered noticeably.  For part of the year these plants discard their leaves and withdraw underground where their rhizomes survive in latency until their next growth season.  So my guess is that these orchids survive in these banks because most other local herbs have trouble coping with the wide seasonal swings in the availability of moisture at these locations.
The inflorescences are long and practically every flower produces a seed pod.   Ackermann speculates in his book on orchids of Puerto Rico and the Virgin Islands that this plant may self-pollinate.   The white flowers are presented in the inflorescence with the lip uppermost.
I have been visiting it over the years to photograph this orchid’s flowers.  Unfortunately the small white flowers are difficult to photograph due to their location, small size and the shady nature of their habitat.   Their location on the roadside bank makes the use of a tripod difficult.  The light conditions at the area change continuously due to a combination of tall trees around the area and the open canopy over the road.   Because they are small the focus has to be sharp but the smallest wind disturbance blurs the picture.  The whiteness of the flower means that using a flash to compensate for the lack of light can wash out all detail of the flowers.  So far I am not satisfied with any of the photos I have taken but fortunately the plants are still thriving in their habitat and can be visited with little trouble.
This plant has no horticultural use that I know of and it is not in cultivation as far as I can tell.  Ackermann classifies it as an uncommon native orchid.

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