Cactus get their name from the Greek word "kaktos," meaning "thistle." One of the most familiar cactus is the aloe vera whose spiny stems are filled with a gel that is soothing to burns. Though slow-growing, some cacti reach heights of 3 to 10 feet, making them popular as beautiful, low maintenance indoor plants.
Cacti are Succulents
Cacti have sharp spines instead of leaves so photosynthesis takes place in the plant's skin or epidermis, which is also the stem. Known as stem succulents, cacti store water so the plant can survive during long periods of drought. The stem of a succulent has the ability to swell as it collects water and then slowly contract as the water is used by the plant.
Areoles and Spines
The spines on true cactus grow from spine cushions, called areole, which occur at evenly spaced intervals over the face of the cacti. In barrel cactus, the areole grow along the ribs. In other smaller species such as the Christmas cactus, they grow along the edges and tips of the pad-like stems. Flowers and shoots emerge from these spiny pads. The areole is unique to the cactus; other plants may have spines but they will not have areole.
Cactus spines not only protect the plant from animals that may eat or otherwise damage its slow-growing stems, they also allow nighttime moisture to condense on them, like dew, where it can drop to the ground and be absorbed by the shallow roots. Spines also work as a wind barrier, reducing the rate of evaporation on hot days.
Cactus as Insect Cultivators
The Aztecs grew Opuntia coccenillifera as hosts to the cochineal scale insect which, when crushed, would produce a rich, purple dye from the female insects and bright red from the males. The dye was then used in fabrics and cosmetics.
Native American Uses for Cactus
Even before Christopher Columbus discovered the cactus, Native Americans were using its sap for medicinal purposes, some of which would produce a narcotic effect. Another, called stenocereus gummosus, was toxic and would stun fish if thrown into water. Cactus fruit could be eaten raw or cooked, made into jam or candied.
Spines were used a toothpicks, combs, sewing needles and fishhooks. The Oerocereus celsianus has long, soft needles that are used to stuff pillows and mattresses
Cactus as a Food
The prickly pear cactus produces a red fruit, called tuna which can be eaten raw or cooked, made into wine or used as a sweetener. The pads, which are flat, hand-sized paddles, are high in vitamins A and C, contain iron and are sometimes extracted for use as a dietary fibre. When boiled, the pads have the flavour of green beans and are a favourite Mexican vegetable.
In central Mexico, the village of Tlaxcalancingo, Puebla, pays tribute to its most important crop, the nopal (prickly pear) cactus, with a fair that features foods made with and from the cactus---among the recipes are tacos de nopalitos and nopal ice cream.