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Guana Island, named for a rock outcropping in the shape of an Iguana's head, sits atop the Puerto Rican Platform along with most of the other British Virgin Islands, all of the U.S. Virgin Islands, and Puerto Rico. This region was a continuous dry land mass during the ice ages when sea levels were much lower (the water was locked in the two mile thick continental ice sheets) and so the islands share many of the same species.
Today the islands exist as mountain tops rising out of the ocean. White calcareous sand and silt, the remains of the shells and skeletons of marine creatures, fills in much of the submerged valleys between the peaks. As one would expect, not every mountain top had the full complement of plant and animal species when the intervening areas flooded with rising sea levels.
The action of man, through logging and the introduction of goats and sheep, further reduced the number of plant species present on the smaller islands. As a result, only three of the four orchid species found growing on Guana Island, Psychilus macconnelliae (listed as threatened or endangered by the New York Botanical Gardens), Tolumnia prionochila, and Epidendrum ciliare are native to the immediate region. Epi. ciliare (found on nearby islands) and a species probably belonging to the genus Schomburgkia have most certainly been introduced to Guana since only a few plants are found growing around the island's small hotel.
Although humid forested areas occur on top of the largest islands, most of the smaller islands like Guana have a fairly dry climate dominated by small trees, scrub brush, and cacti. The wet hurricane season begins in September/October and follows a hot, summer dry season. Constant trade winds blow over these islands at all times, and even though short rain showers (often lasting only a few minutes) may occur every few days in the dry season this water quickly evaporates and the vegetation suffers.
The orchids are adapted to these conditions in various ways and are often encountered growing under the harshest conditions.
A few clumps of Epi. ciliare are scattered around the hotel grounds mounted to trees at waste to chest height. These plants have grown well without aid of human care for many years.
Long ropes of roots can be seen here extending for over two meters into the ascending branches. This causes whatever nutrients that may be washed from the tree's leaves and bark to be funneled into the absorbent mass of living and dead roots at the base of the plant.
In addition to the nutrients coming to the plant from runoff, the tangled root mass provides a home for insects, spiders and lizards, all of which bring back and deposit nutrient rich waste products after their daily/nightly feeding excursions to the branches above or the ground below the orchid. Decaying leaves that fall among the pseudo bulbs also decay and provide the plant with nutrients.
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This plant is obviously healthy, growing well, and had successfully flowered the previous season (as can be seen by the many seed capsules), but unlike plants grown under close human supervision, this plant is full of black and yellow blotches on the leaves, and the only pseudo bulbs that are not shriveled are those that are immature and still growing.
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A related species, Psychilus macconnelliae, one of the two truly wild growing orchids on the island seems to use a different strategy to secure water and nutrients. Instead of heading up to gather and funnel runoff water, long strands of roots most often ran down the trunks of the small trees for a meter or more to the the rocky soil below. There they extended under the leaf litter along the top of the rocky soil. |
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 This species was observed growing in the open along the tops of the peaks and ridges of the western side of the island. And although it was found growing in light shade on the trunks of small trees (never any higher than about two meters from the ground), it was most often found at waste height or below growing on cacti, small trees or rocks mostly exposed to the direct sun. |
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By far the most impressive feat witnessed concerning P. macconnelliae was its ability to exist in the harshest conditions the island had to offer. Here it is seen in a common lithophytic habit growing in a semi protected crack in the rock. This in itself is not to out of the ordinary for many orchids. The Schomburgkia sp. mentioned earlier was found growing on top of a large intact boulder in full sun (but it was obviously placed there and probably cared for until it became established. |
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Here is another plant found growing on bare rock. The roots can clearly be seen running over the rock in the close up. This stunted plant is growing and flowering in direct sun on the windward side of the island. Here atop a cliff it is exposed to salt air from the waves three stories below. |
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