Letís start with some true/false questions that will be answered in this article.
1. All cacti are succulents.
2. All cacti have spines
3. Cacti have no leaves.
A definition of cacti might be as follows. Cacti are succulent, spiny, flowering plants that for the most part have no leaves.
Now, letís look at each term used in that definition. Cacti are succulents, but all succulents arenít cacti.
With few exceptions, all cacti have spines. The exceptions include unusual ones like the spineless prickly pear. Each individual spine grows from a tuft of bristles, wool, or hairs called an areole.
Areoles are unique to the cacti. These cushion-like plant structures are distributed on the surface. Theyíre the growing point of the plant. Blooms arise from these points as well.
The spines serve several functions. Apparently, they evolved to help provide the plant with protection from animalsóincluding humans. Though itís true all cacti may have spines, they arenít as lethal in some species.
Generally, it is true that cacti have no leaves. As with the spines, the exceptions prevent this from being a hard and fast rule. One particular group of cacti with true leaves is the Pereskias. For other species, the modified stems assume the role of leaves, and also serve as a reservoir for water storage. Often the stems are ribbed or shaped so that very little surface is exposed to the hot sun at any given time.
Cacti are flowering plants. For the most part, they produce single or simple blooms produced right from the areoles. The exception is the Pereskias, which have multiple flowers per bunch. Donít bother looking for flower stalks or flower stems. There simply arenít any. They have multiple blooms.
In the Southwestern U.S., the flowers are often pollinated in the spring by bats migrating north for the summer. Later in the fall as they make the return trip, they eat the cactus fruits and disperse seeds in their droppings into new locations.
When one hears the word cacti, the desert may immediately come to mind. However, they are widely dispersed. Just in case you thought all of them needed a warm climate, consider the ones grow in chilly areas of Patagonia and Chile. They can be found from the Arctic Circle south to Canada and the U.S. to Central America, the West Indies, and South America. Over 2000 species are known. Despite this wide distribution, most are native to the U.S., Mexico, and South America.
Broadly speaking, cacti are divided into two groups-desert and jungle. The two kinds have evolved to withstand the adverse growing conditions of their native lands.
About 40-50 million years, the New World was a veritable jungle with lots of lakes and vegetation. Over time as the climate changed, the cacti adapted and evolved to suit the harsher growing conditions. The stems enlarged to become reservoirs for water, while leaves disappeared for the most part. Plant growth slowed, and the fleshy stems assumed the roles formerly fulfilled by leavesóphotosynthesis, which taps the sunís energy for plant food.
With the harsh, hot arid environment, it is easy to see why cacti could
have evolved in the desert Southwest. However, the jungle species faced challenges too. Many evolved and survived in wet, tropical areas of Brazil by going to great heights. There they grow in the trees just as orchids and bromeliads do. These are called epiphytic cacti. Unlike their sun-loving Southwestern relatives, these tree-dwelling jungle species prefer somewhat shady conditions. Too much sun can be harmful, especially during the summer months.
The exact shape and size of cacti vary considerably from small tiny pebble-like species to tall, multi-armed columnar ones, such as the giant saguaro.