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Oreocereus is a plant genus that is part of the Cactaceae family. It contains about 11 species of cacti that are native to the Andes Mountains in South America. The cacti are column shaped and feature long, white hairs that drape over sharp spikes. They are commonly used as container plants. Over-watering is a common problem with this genus, and insects cause damage to these plants.
The genus name is a Greek word which means "mountain Cereus." Commonly, the plants in the Oreocereus genus are referred to as "old man of the Andes," or "old man of the mountains." This describes the gray or white strands on the cacti and their location; they are usually perched high atop the landscape on the edges of the Andes Mountains.
Oreocereus celsianus is distributed throughout Bolivia, Peru, and northern Argentina. Oreocereus doelzianus is located mainly in the Andes of central Peru, while Oreocereus ritteri is native to Boliva. Oreocereus leucotrichus grows in northern Chile and southern Peru.
The old man of the Andes typically grows 10 feet (3 m) in height and 4 inches (10 cm) wide. It features red or straw colored needles that poke through a mesh of white strands that are equally sharp. The white strands are thought to protect the plant from the intense desert sun. This cacti has stems that branch with age.
It usually takes several years before this plant can produce flowers. When the old man of the Andes does bloom, it typically occurs during the summer months. The purplish-violet flowers are 3-4 inches (7-10 cm) long and tubular in shape.
It is important to provide adequate environmental conditions when growing a cactus such as the old man of the Andes. It generally prefers well-draining, fertile soil. Sandy soil that is highly porous is generally used since it provides adequate moisture retention for this plant. Watering should be kept to a minimum, since the cactus will rot easily if over-watered, especially during the winter. The cactus should be grown in full sunlight.
Cacti within the Oreocereus genus are susceptible to infestation by the red spider mite. This insect is classified as a mite but produces webbing similar to a spider. It feeds on the outer layer of the cactus, and the affected areas appear brown. The best way to treat the plant is to apply a pesticide that is designed for the red spider mite.