Cholla wood that doesn't come from trees but is actually a product of the cholla cactus. When these cacti die and dry out, cholla wood remains.
Benefits of cholla wood
Although cholla wood is definitely a visually interesting addition to the aquarium, most aquarists don't use its for its decorative value. It's added to the aquarium because shrimp love it!
Unlike most types of wood that are used in the aquarium, cholla is soft and breaks down over time. During this process all kinds of beneficial processes happen. As with Indian almond leaves and alder cones, tannins are released into the water. This can stain the water a slight yellow colour, which some consider unsightly but actually helps imitate the natural habitat of many shrimp species. Most importantly, though, tannins have antibacterial and anti-fungal properties which help protect your shrimp against disease.
As cholla wood breaks down a layer of biofilm forms on it. This makes it the perfect place for shrimp to forage; a piece of cholla wood will likely have a few shrimp on it at any given time.
Lastly, because cholla is hollow and holey it makes a great hiding place for shrimp, which means you can use it as a natural looking alternative to ceramic shrimp flats. Shrimp will especially appreciate it while molting, when they're very vulnerable and like to be able to retreat to a safe place.