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Cactaceae Open discussion of Cacti and related species

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Old 08-12-2011, 03:10 AM
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Default Opuntia Megasperma question

With the absence of turtles will this opuntia form the huge (solitary) trunk it forms in habitat? From my understanding the turtles eat the lower pads forcing the plants to grow taller. I have been watching the galapagos opuntias at lotusland for a while and it seems that Opuntia echios var. gigantea and Opuntia galapageia form solitary trunks regardless of anything trying to eat it but the megasperma has multiple branches at the base. Will these branches fuse (or die) at some point to form a mega trunk or are the turtles really responsible for the plants appearance?

Megasperma seems to be endemic to Floreana, San Cristobal and Espanola. All of which had turtles at one point. The subspecies of Chelonoidis nigra on Floreana is thought to have gone extinct by 1850. Could it be that the plant at lotusland is from seed collected from Floreana and with out turtles is becoming less of a tree?

I have also notice that opuntia quimilo (Argentina, Bolivia) starts off fairly shrubby but at some point becomes a small tree (with a solitary trunk). It's just the transition stage I don't understand.


Last two photos are echios and galapageia.
Now that I'm looking at the photos it seems the branches just fuse.
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Old 08-12-2011, 11:28 PM
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Default

It should form a trunk without intervention. The shape of the pads (and maybe morphology) changes as the stems get further from the roots, producing the trunk.

T
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Old 08-15-2011, 03:41 PM
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Default Galapagos Opunitas - Are They the Same?

Here is the abstract of an article I am ordering on the Galapagos Opuntias and how they appear more closely related than thought before.

"Due to the pronounced morphological variation and geographical distribution of Galápagos' Opuntia cacti, numerous hypotheses have been advanced regarding their radiation, diversification, and classification. The currently accepted classification is based on morphology and recognizes six species and fourteen varieties, but the plasticity of many of the characteristics renders any morphological taxonomy problematic. Our analysis of previously published morphological data agrees only partially with the current classification. We present the first molecular phylogeny of these plants. Multiple DNA sequences indicate little genetic distinction among the currently identified species, despite restricted gene flow and limited long distance dispersal within the archipelago. No clear relationship exists between morphological and genetic differences. These results suggest that both molecular and morphological data should be used in conservation planning. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 451–461."
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