Wednesday, August 31, 2011

Galapagos Plants

Opuntia Cactus Forest on Rabida
You would expect an island on the equator in the middle of the Pacific Ocean to be full of lush tropical vegetation. Yet the Galapagos surprises us in this aspect, just as it does with all the animals. There are only some 600 native species and subspecies of plants in the archipelago, compared to over 20,000 on mainland Ecuador only 600 miles away. 250 of these are endemic to Galapagos, having evolved from an original 110 species which arrived by natural means. The Adaptive Radiation found with finches and tortoises applies to plants as well.  If I failed to make a post here about the plants, my friend Tavia (a wildflower expert) would have my hide! Actually, I'm surprised at how many plant photos I have, especially since our guides didn't point out many plants unless we asked about them.
Vegetation Zones
Here's the biggest issue plants have on the Galapagos - lack of water. There are two seasons, the wet warm season, and the cool dry season, also called the garua. Prevailing winds from the southeast blow moisture in, but it only benefits one side of an island, and the higher the island is, the more moisture it receives on that side. The other side is in the "rain shadow" (Hawaii has the same problem.), and vegetation there must adapt to the arid conditions. The coastal areas, of course, require plants that are salt tolerant. Santa Cruz was the only island we visited with enough altitude for several of these vegetation zones. The other smaller lower islands were primarily in the arid zone only. Remember, many islands have no natural source of fresh water other than the rains and garua mists.

Garua Mist

Misted Cactus Needles

Almost every morning when we awoke, we saw heavy mist over the island outside our ship. Sometimes it remained till 10 or so before lifting. Plants have adapted to use whatever moisture is available during these months, until the rains come...if they do.
Palo Santo - ghost trees
Another plant adaptation is to cease making chlorophyll when there is insufficient moisture. These Palo Santo trees are also known as the "ghost forest" with their pale white color in the dry season. Actually, the bark on this tree is a darker color; the pale color comes from lichens growing on them. When it rains they will turn green, sprouting leaves and blossoms. The name "holy stick" comes from its habit of coming into leaf around Christmas time, and from its use as incense.

Sesuvium on South Plaza Island
Sesuvium also preserves its life by going dormant in the dry season, but it turns red and yellow instead of white, so the ground looks as if it's covered by autumn leaves.
Cactus Finch Nest
The Opuntia is a giant prickly pear cactus, and thus easily recognizable. There are six species and 14 varieties of opuntia. In the arid regions, it fills the role of trees and forests, since there isn't enough moisture for trees. On islands where the animals eat cactus, the needles are sharp, as expected, and it grows tall to evade being munched on. Rabida has no tortoises and the opuntia are low and sprawling. On islands with no cactus eaters though, the needles are soft and pliable.  Tortoises and iguanas eat the pads, while bird species eat the flowers, fruit, seeds and even extract water from the pads.
Candelabra Cactus - Santa Fe Island
Candelabra cactus can grow up to 24 feet high, with purple flowers and globular edible fruit. When it dies, a hollow woody skeleton is left behind.

Lava Cactus - Bartolome Island
But my favorite is the ultra-hardy and persistent lava cactus. Yes, just as the name indicates, they grow on bare black dry lava, where almost nothing else can exist. The young ends of each cactus are yellow, and they turn as grey-brown as they age.

Mollugo on Bartolome Island
This little mollugo plant grows (albeit slowly, I suppose) on the pahohoe lava fields of Bartolome.

Cutleaf Daisy on Floreana Island
Our guides did note that for some reason, most flowers are yellow, and the Galapagos sulphur butterfly is one of the pollinators. This cutleaf daisy is endemic to Floreana...
Galapagos Cotton
...while the Galapagos cotton is more widely seen. After it blooms, the seed pod actually opens to produce a white lint or cotton used by birds for nest linings!

Muyuyu - Yellow Cordia
The muyuyu, or yellow cordia, produces a white seed which early settlers used to make glue or starch, since it's very sticky.

Galapagos Tomato
Once again, we found a very familiar plant in an unfamiliar location. Yes, what looks like a tomato is really the Galapagos tomato, with small edible red fruit. There are also Galapagos species of passion flower, mistletoe, mesquite, guava, and aster.
Galapagos Lantana
Yes, there are non-native invasive plants, just as you would expect, and invasive insects like this wasp on a native lantana and fire ants.
Tequilia on Bartolome Island
It's easy for plants to grow where there is water. I admire the tough guys like this tequilia that hang on in a dry, rocky, barren, otherwise lifeless lava field like this. Way to go guys!

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