Cleistocactus Stausii

Latin name: Cleistocactus Straussi

Common name: Silver Torch Cactus

Appearance: Tall, greyish green stems which are covered in fine yellowish or whitish hairs.

Height: Up to 3 metres tall

Origin: South America countries such as Bolivia and Argentina

The Cleistocactus Stausii stem is almost entirely (80/90%) parenchyma tissue which stores water and so loses much less water than an ordinary mesophytic plant.

Cacti of dry (arid) conditions can withstand a huge water loss that would kill normal plants – it can live even with a loss of 60% of its water.

The Silver Torch Cactus is a xerophyte and so is adapted to harsh, dry conditions. These adaptations are:

Cacti have thick cuticles that limit the loss of water. This means that they have the ability to survive in dry conditions where there is little rainfall. However this cuticle also prevents CO2 from diffusing into the body of the cactus. This is because CO2 molecules are larger than water molecules and so the water would diffuse out of the cactus quicker than CO2 diffused into it. Therefore it only allows CO2 to diffuse into the cactus (TRANSPIRATION) during the night as this keeps the loss of water to a minimum.
For photosynthesis to take place CO2 is needed and so the cactus stores the CO2 gained from transpiration during the night and this is used up during the day by photosynthesis. The storing of CO2 during the night is called "succulent metabolism".
It has multiple tiny hairs covering each stem. This traps a layer of moist air, which reduces the plant air-water concentration gradient, and so as a result reduces transpiration, this means that the plant retains more water.
The hairs also help to shade the plant, keeping it cool. This reduces water lost through transpiration.
The fact that cacti have no leaves means that less water is lost by transpiration.
Cacti are protected from predators in two ways – it has spines and also a tough cuticle (which also protects it from the heat).
In order to have the best chance of survival, the cactus sprouts just after the dry season when the most water is available for its early part of life.
During the dry period water evaporates at such a quick rate the cacti need to have an adaptation to allow it to absorb as much water as possible when it is available. This adaptation is it’s wide root system.