Dallas Krentzel
Galapagos prickly pear (Opuntia echios var. gigantea) forest on the coast of Santa Cruz, Galapagos Islands, Ecuador
Unfortunately there is no good scale in this photo, but I can tell you the cacti in the foreground on the right are something like 3.5 - 4.0 m tall (11 - 14 ft), or about twice as tall as a person. That means that, yes, as you might have already guessed, the cactus on the left is really tall, potentially approaching 8 m (~26 ft). The upper range for this species is around 12 m (~40 ft), and I saw a few of these on my trip. They're pretty incredible, considering that every other Opuntia in the world is a puny shrub (although Brasilopuntia, a related genus in South America, can get very tall as well).
I had previously labeled these cacti as Opuntia echios var. echios on this photostream; however, after searching the scientific literature I've discovered this designation was innaccuate. Opuntia echios is the only Opuntia species on Santa Cruz, however, there are two recognized varieties, var. echios in the north and var. gigantea in the south. These varieties were named for their morphological differentiation, however, recent genetic work with both microsatellites and ribosomal genes have determined that these varieties do don't differ genetically, with over 95% of existing genetic variability existing within localities rather than between localities of different varieties. This is interesting, because despite the lack of genetic divergence between the varieties, var. echios are small, shrub like plants with dense covering of spines, while the var. gigantea are arboreal (tree-like) plants with large robust trunks and and multiple branchings containing more sparsely spined pads. Is there a genetic basis to this differention that has evolved within very recent times, such that both populations retain overall similar genomes, or is this morphological variability simply due to regional environmental differences, which has been observed in other cacti? Who knows. There are many intermediate individuals at hybrid zone localities, but this is compatible with both models. TIme will tell...
Helsen, P., P. Verdyck, A. Tye, S. Van Dongen. 2009. Low levels of genetic differentiation between Opuntia echios varieties on Santa Cruz (Galapagos). Plant Systematics and Evolution 279:1–10.
Helsen, P., R. A. Browne, D. A. Anderson, P. Verdyck, S. Van Dongen. 2009. Galápagos' Opuntia (prickly pear) cacti: extensive morphological diversity, low genetic variability. Biological Journal of the Linnean Society 96(2): 451–461.
For a discussion on why Opuntia of the Galapagos are so neat, and their relationship with the endemic giant tortoises, see this image: www.flickr.com/photos/31867959@N04/6012346984/in/set-7215...
For a discussion on why I find Opuntia so neat morphologically, developmentally, and functionally: see this image: www.flickr.com/photos/31867959@N04/7457728654/in/set-7215...
Galapagos prickly pear (Opuntia echios var. gigantea) forest on the coast of Santa Cruz, Galapagos Islands, Ecuador
Unfortunately there is no good scale in this photo, but I can tell you the cacti in the foreground on the right are something like 3.5 - 4.0 m tall (11 - 14 ft), or about twice as tall as a person. That means that, yes, as you might have already guessed, the cactus on the left is really tall, potentially approaching 8 m (~26 ft). The upper range for this species is around 12 m (~40 ft), and I saw a few of these on my trip. They're pretty incredible, considering that every other Opuntia in the world is a puny shrub (although Brasilopuntia, a related genus in South America, can get very tall as well).
I had previously labeled these cacti as Opuntia echios var. echios on this photostream; however, after searching the scientific literature I've discovered this designation was innaccuate. Opuntia echios is the only Opuntia species on Santa Cruz, however, there are two recognized varieties, var. echios in the north and var. gigantea in the south. These varieties were named for their morphological differentiation, however, recent genetic work with both microsatellites and ribosomal genes have determined that these varieties do don't differ genetically, with over 95% of existing genetic variability existing within localities rather than between localities of different varieties. This is interesting, because despite the lack of genetic divergence between the varieties, var. echios are small, shrub like plants with dense covering of spines, while the var. gigantea are arboreal (tree-like) plants with large robust trunks and and multiple branchings containing more sparsely spined pads. Is there a genetic basis to this differention that has evolved within very recent times, such that both populations retain overall similar genomes, or is this morphological variability simply due to regional environmental differences, which has been observed in other cacti? Who knows. There are many intermediate individuals at hybrid zone localities, but this is compatible with both models. TIme will tell...
Helsen, P., P. Verdyck, A. Tye, S. Van Dongen. 2009. Low levels of genetic differentiation between Opuntia echios varieties on Santa Cruz (Galapagos). Plant Systematics and Evolution 279:1–10.
Helsen, P., R. A. Browne, D. A. Anderson, P. Verdyck, S. Van Dongen. 2009. Galápagos' Opuntia (prickly pear) cacti: extensive morphological diversity, low genetic variability. Biological Journal of the Linnean Society 96(2): 451–461.
For a discussion on why Opuntia of the Galapagos are so neat, and their relationship with the endemic giant tortoises, see this image: www.flickr.com/photos/31867959@N04/6012346984/in/set-7215...
For a discussion on why I find Opuntia so neat morphologically, developmentally, and functionally: see this image: www.flickr.com/photos/31867959@N04/7457728654/in/set-7215...