Cactuses or Cacti: A Guide to Types, Care, and Uses

Cactuses are incredibly diverse, with over 1,500 species found in the wild. They come in a range of shapes and sizes, from the tiny Living Rocks to the towering Saguaro.

One of the most interesting things about cactuses is their unique ability to store water in their stems. This adaptation allows them to thrive in arid environments where other plants would wither and die.

Some popular types of cactuses include the Prickly Pear, which is edible and can be used to make jam and other treats. The Prickly Pear is also a popular choice for gardeners due to its ease of care.

Whether you're a seasoned gardener or a beginner, cactuses are a great choice for adding some unique flair to your indoor or outdoor space.

Cacti have been around for a long time, with fossil records showing they've been thriving on Earth for over 30 million years.

Most cacti are found in the Americas, with the largest number of species in Mexico and the southwestern United States.

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Cacti are incredibly diverse, with over 1,500 species ranging in size, shape, and color.

Some cacti can store up to 200 liters of water in their stems, allowing them to survive for months without rain.

Cacti have adapted to survive in arid environments, often with thick, waxy stems that prevent water loss.

Cacti can thrive in a wide range of temperatures, from freezing cold to scorching hot.

Cacti have evolved to protect themselves from predators, often with sharp spines that deter animals from getting too close.

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The stems of cacti are truly one-of-a-kind, adapted to store water and withstand harsh conditions. They can be smooth, covered in tubercles, or even have a waxy appearance. The surface of the stem may be green, bluish, or brownish green, containing chlorophyll and able to carry out photosynthesis.

Some cacti have stems that can swell up to 90% water, making their ribs almost invisible. But when they're short on water, those same ribs become very visible. The stems of most cacti are also visibly waxy.

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The areoles on cacti stems are a remarkable feature, producing spines and flowers. They're highly specialized, condensed shoots or branches that can be circular, oval, or even separated into two parts. In most cacti, areoles become inactive after a few years, resulting in a fixed number of spines and flowers produced from the ends of stems.

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Spines are a defining feature of cacti, and they come in a wide range of shapes, sizes, and colors. They're modified leaves, to be precise, and can be found even on cacti with leaves, like Pereskia and Pereskiopsis.

Most cacti have spines that emerge from areoles, which are woolly or hairy areas on the stems. These spines can be straight or slightly curved, and are often described as hair-like, bristle-like, needle-like, or awl-like.

The number, color, size, shape, and hardness of spines can vary greatly between species, making them a useful tool for identification. Some cacti have flattened spines, while others have hooked spines, and some even have spines that are barbed along their length.

The subfamily Opuntioideae is particularly notable for its glochids, which are short, barbed spines that are easily shed and can cause long-lasting irritation. These tiny spines are a common feature of opuntias, and are often the first thing you notice when handling one of these plants.

Here are some examples of the varied spines found on cacti:

Whether you're a seasoned cactus enthusiast or just starting out, it's worth taking a closer look at the spines on your plants. They're not just a nuisance to be removed - they're a vital part of what makes cacti so unique and fascinating.

Most ground-living cacti have only fine roots, which spread out around the base of the plant for varying distances, close to the surface.

Some cacti have taproots, which can be quite large and voluminous, like in the Ariocarpus genus.

These taproots may aid in stabilizing the larger columnar cacti, helping them stay upright and secure.

Climbing, creeping and epiphytic cacti often have adventitious roots, which are produced along the stems where they come into contact with a rooting medium.

Cacti come in a wide variety of growth habits, making them one of the most fascinating plants out there. From tree-like to shrubby, columnar to globular, and even epiphytic, the diversity of cacti is truly remarkable.

Some cacti, like those in the genera Leuenbergeria, Pereskia, and Rhodocactus, have branches covered with leaves, making them look more like other plants. In contrast, most other cacti have branches that are bare of leaves and bark, covered with spines instead.

Cacti can grow to be quite large, with some species becoming tree-sized without branches. Take the larger specimens of Echinocactus platyacanthus, for example. They can grow to be quite impressive in size.

Smaller cacti, on the other hand, are often described as columnar. They consist of erect, cylinder-shaped stems, which may or may not branch. The boundary between columnar forms and tree-like or shrubby forms is difficult to define.

Here are some examples of different growth habits:

All cacti have adaptations to promote efficient water use, making them well-suited to hot and dry environments. Most cacti specialize in surviving in these conditions, but a small number of species have adapted to life as climbers or epiphytes in tropical forests.

Some cacti have stems that are even smaller and more ball-shaped, making them globular in appearance. These globular cacti may be solitary or form clusters that create large mounds.

Cacti have evolved to conserve water in a variety of ways, making them incredibly resilient in harsh environments.

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Classification can be a tricky business, especially when it comes to cacti. Botanists have been trying to get it right for centuries.

The International Cactaceae Systematics Group (ICSG) was formed in 1984 to produce consensus classifications down to the level of genera. Their system has been the basis for subsequent classifications.

Cacti have been divided into around 125-130 genera and 1,400-1,500 species, which are then arranged into tribes and subfamilies. The ICSG classification recognized four subfamilies, the largest of which was divided into nine tribes.

The subfamilies are: Pereskioideae, Opuntioideae, Maihuenioideae, and Cactoideae. Molecular phylogenetic studies have supported the monophyly of three of these subfamilies, but not Pereskioideae.

A 2011 study found that only 39% of the genera in the subfamily Cactoideae sampled in the research were monophyletic. This means that classification of the cacti currently remains uncertain and is likely to change.

Here are the four subfamilies of cacti recognized by the ICSG:

Semi-desert cacti need careful watering, as more are lost due to untimely water application than any other reason.

During the growing season, cacti should be allowed to dry out between thorough waterings. A water meter can help determine when the soil is dry.

Brown recommends providing some water even during the dormant winter season, but other sources suggest withholding water during this time.

For a mixed collection, a minimum temperature of between 5 °C (41 °F) and 10 °C (50 °F) is often suggested, except for cold-sensitive genera like Melocactus and Discocactus.

Some cacti, like Rebutia minuscula, are fully frost-hardy when kept dry and may flower better when exposed to a period of cold.

Growing cacti in containers requires a suitable growing medium that provides support and stores water, oxygen, and dissolved minerals. A high air content is essential for cacti.

Using a mixture of two parts commercial soilless growing medium, one part hydroponic clay, and one part coarse pumice or perlite is a suggested approach. This combination can provide the necessary air content and water retention for cacti.

Roger Brown recommends adding soil from earthworm castings to the mixture for extra nutrients. However, not everyone agrees on the use of organic material.

A general recommendation is to use 25-75% organic-based material, with the rest being inorganic such as pumice, perlite, or grit. This balance can provide the necessary support and water retention for cacti.

Some growers, like Hecht, recommend using coarse sand as the basis of a growing medium, especially for non-epiphyte cacti that prefer soil low in or free of humus.

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Watering is a critical aspect of cactus care. More cacti are lost through the untimely application of water than for any other reason.

Cacti need some water even during the dormant winter season. Brown recommends not withholding water entirely during this time.

The frequency of watering depends on the growing conditions, but a general rule is to allow cacti to dry out between thorough waterings. Regular re-potting is recommended if you need to use hard water to avoid the build-up of salts.

A water meter can be a helpful tool in determining when the soil is dry.

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Semi-desert cacti may need some shading when exposed to high light levels in a greenhouse, especially during summer. This is because high light levels and temperatures can be challenging for them.

Allowing the temperature to rise above 32 °C (90 °F) is not recommended. This can cause stress to the cacti.

The minimum winter temperature required for cacti varies depending on the species. For a mixed collection, a minimum temperature of between 5 °C (41 °F) and 10 °C (50 °F) is often suggested.

Some cacti, like those from the high Andes, are fully frost-hardy when kept dry. This means they can tolerate temperatures down to -9 °C (16 °F) in cultivation.

Propagation of cacti can be done through seed, cuttings, or grafting. Seed sown early in the year produces seedlings that benefit from a longer growing period.

For seed propagation, it's essential to keep the growing medium moist but not waterlogged, as this can cause both seeds and seedlings to rot. A temperature range of 18-30 °C (64-86 °F) is suggested for germination, with soil temperatures of around 22 °C (72 °F) promoting the best root growth.

Cuttings can be made from parts of the plant that can grow roots, such as pads or joints. These cut surfaces should be allowed to dry for a period of several days to several weeks until a callus forms over the cut surface. Rooting can then take place in an appropriate growing medium at a temperature of around 22 °C (72 °F).

Some pests that attack cacti in cultivation include mealybugs, scale insects, whiteflies, red spider mites, and thrips. Mealybugs and scale insects feed on sap, while whiteflies and red spider mites suck sap, causing damage to the cactus.

Here are some common pests that attack cacti:

Fungi, bacteria, and viruses can also attack cacti, with fungi and bacteria often entering through wounds or over-watering. Fusarium rot is a type of fungal disease that can cause rotting accompanied by red-violet mold.

Propagation is a crucial step in cactus cultivation, and there are several methods to achieve it.

Seed sown early in the year produces seedlings that benefit from a longer growing period.

A very wet growing medium can cause both seeds and seedlings to rot, so it's essential to maintain a balance of moisture.

A temperature range of 18–30 °C (64–86 °F) is suggested for germination, and soil temperatures of around 22 °C (72 °F) promote the best root growth.

Low light levels are sufficient during germination, but afterwards semi-desert cacti need higher light levels to produce strong growth.

Reproduction by cuttings makes use of parts of a plant that can grow roots, and some cacti produce "pads" or "joints" that can be detached or cleanly cut off.

It's recommended that any cut surfaces be allowed to dry for a period of several days to several weeks until a callus forms over the cut surface.

Grafting is used for species difficult to grow well in cultivation or that cannot grow independently, and it's often used for chlorophyll-free forms with white, yellow or red bodies.

In commercial production, huge numbers of cacti are produced annually, with 49 million plants propagated in Korea alone in 2002, valued at almost US$9 million.

Pests can be a real nuisance when growing cacti. Mealybugs, scale insects, and red spider mites are common pests that feed on cactus sap, causing damage and discoloration.

Some pests are resistant to insecticides, but biological controls are available to combat them. Thrips, in particular, target flowers and can be a problem.

Fungus gnats and sciarid fly larvae can eat cactus roots, while slugs and snails will munch on the plant itself.

Fusarium rot can enter through a wound and cause rotting, accompanied by red-violet mold. This is often a result of over-watering.

Cacti can also be attacked by Helminosporium rot, caused by Bipolaris cactivora, and Phytophthora species, which cause similar rotting. Fungicides may not be effective in combatting these diseases.

Several viruses, including cactus virus X, have been found in cacti. These viruses can cause limited visible symptoms, such as chlorotic spots and mosaic effects.

Some cacti are used for human food and as fodder for animals, usually after burning off their spines.

The Opuntia species are employed in herbal medicine, and their use has spread from the Americas to other regions like India.

Cochineal, a red dye produced by a scale insect on Opuntia species, has seen a rise in demand for natural dyes, leading to commercial production.

Living cactus fences are used as barricades around buildings to prevent people breaking in, and the woody parts of cacti are used in buildings and furniture.

The saguaro (Carnegiea gigantea) is used in the frames of wattle and daub houses built by the Seri people of Mexico.

Cactus flowers are quite unique and variable in appearance. They can have a wide range of shapes and sizes.

Some cacti produce floral tubes without wool or spines, like the Gymnocalycium, while others have areoles that produce wool and spines. This is a notable difference between species.

Cactus flowers usually have many stamens, but only a single style, which may branch at the end into more than one stigma. This is a key characteristic of cactus flowers.

Pereskia flowers are a notable exception, as they may be borne in clusters. This is a distinct feature of this particular species.

The stamens of cactus flowers often arise from the inner surface of the upper part of the floral tube. This can vary in different species, with some having stamens produced in specific areas.

Cacti have been cultivated as ornamental plants for centuries, with enthusiasts in Europe collecting and growing them as early as the 1800s.

Rare plants were sold for very high prices, and suppliers of cacti employed collectors to obtain plants from the wild, in addition to growing their own.

In regions unsuited to outdoor cultivation, such as northern Europe and North America, cacti are often grown in greenhouses. They can be kept in pots or grown in the ground.

Cacti are also grown as houseplants, many being tolerant of dry atmospheres. They can be placed outside in the summer to ornament gardens or patios, and then kept under cover during the winter.

Less drought-resistant epiphytes, such as epiphyllum hybrids and Schlumbergera, are widely cultivated as houseplants.

Cacti are used as construction materials, with living cactus fences serving as barricades around buildings to prevent break-ins and corraling animals. The woody parts of cacti are also used in buildings and furniture.

Some cacti, like Cereus repandus and Echinopsis atacamensis, have woody parts that can be used in construction. Their frames are sturdy enough to support a house.

Cochineal, a red dye, is produced by a scale insect that lives on certain species of Opuntia. It's been used for centuries by people in Central and North America.

The demand for cochineal fell when synthetic dyes became available in the 19th century, but it has since increased due to a rise in demand for natural dyes.

The Saguaro, a cold-hardy columnar cactus, is widespread in the Arizona Upland subdivision of the Sonoran Desert. This area experiences frequent frosts, making the Saguaro a standout.

You can find several smaller columnar species in the Sonoran Desert, as well as many more in the adjacent tropical communities. The Myrtillocactus cochal, from Baja California, branches profusely from a short trunk, forming a large candelabra-shaped mass of stems up to 13 feet tall and wide.

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Bergerocactus emoryi, also from Baja California, has very slender stems to about 7 feet tall, densely clothed with yellow spines. Its fruit is very bristly and used as a hair brush.

Here's a brief overview of some giant columnar cacti species:

These cacti are not just visually striking, but also have unique characteristics that make them stand out.

The Sonoran Desert is home to some truly remarkable cacti, and I'm excited to share some of the most interesting species with you.

The Saguaro is one of the most iconic cacti in the Sonoran Desert, and it's the only columnar cactus that's widespread in the Arizona Upland subdivision.

One of the most fascinating things about the Saguaro is that it's sufficiently cold-hardy to thrive in areas with frequent frosts.

The Organpipe cactus is another notable species found in the Sonoran Desert, and it's characterized by its unique, pipe-like stems.

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The Senita cactus is a smaller, but equally impressive, columnar cactus that's found in the Sonoran Desert.

The Cardon cactus, also known as Pachycereus pecten-aboriginum, is a thornscrub species that's found in southern Sonora and southern Baja California.

The Cardon cactus has a very bristly fruit that's used as a hair brush, which is a pretty clever use for a cactus's produce.

Myrtillocactus cochal, also known as the cochal, is a candelabra-shaped cactus that's found in Baja California. It's a pretty short-lived cactus, living only a few decades.

Bergerocactus emoryi, or the golden torch cactus, is a slender-stemmed cactus that's found in Baja California. It's densely clothed with yellow spines, which is a pretty striking feature.

The Genus Cactaceae is a large and diverse group of plants, with over 175 species worldwide. This includes the popular Mammillaria genus, which is the largest of the diminutive cacti.

Mammillarias are known for their small size, with most species being less than 6 inches tall. They have closely-spaced areoles bearing many spines that obscure the body of the plant.

Some species of Mammillaria have hooked central spines, which is a distinguishing feature from other genera. The fruits of Mammillarias are edible, but their small size makes them difficult to gather in significant quantities.

The genus ranges from southern California to central Texas and southward through Central America. About 25 described species occur in the Sonoran Desert.

These plants often go through "boom-and-bust" population cycles, with some species experiencing vast population declines after catastrophic events. Mammillaria thornberi, for example, was once found in countless millions in the Avra Valley west of Tucson, but its population all but disappeared after a freeze in 1937.

Cacti is the Latin plural of cactus, and it's the more popular usage among English speakers. This is because cacti has been used since the plant was first classified.

Cacti is also the preferred form among dictionaries, which recognize both cacti and cactuses as correct. However, cactuses is the plural form that follows standard English grammatical rules.

The choice between cacti and cactuses ultimately comes down to personal preference, as both forms are acceptable. But if you want to sound like a native speaker, cacti is the way to go.

Interestingly, the English habit of changing the vowel in plurals comes from German, or Germanic languages. This is why we have words like "tooth" becoming "teeth" and "truth" becoming "truths".

In terms of possessive form, cacti's is the correct form, as Jeffrey Howes pointed out in the comments. This is because cacti is the subject of the sentence, making it the correct form to use.

Here's a quick rundown of the key points:

So, whether you choose cacti or cactuses, you can't go wrong. Just remember that cacti is the more traditional form, while cactuses is the more grammatically correct form.

The cactus family is nearly endemic to the New World, spanning from southern Canada to southern South America. This means you won't find many cacti in the Old World, except in a few regions where they've been introduced and have gone wild.

Cacti are most common in semiarid habitats with low rainfall, but with dependable rainy seasons. This is because they've adapted to thrive in areas with limited water availability.

One notable exception is the Sonoran Desert region, which is home to about 300 species of cacti.

Conservation efforts are crucial for protecting cacti, and some species are more vulnerable than others. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) lists all cacti in Appendix II, which means international trade is closely controlled to prevent over-collection and extinction.

The main threats to cacti in the wild are development, grazing, and over-collection. Development can come in many forms, such as the construction of dams or highways that destroy habitats.

Grazing by introduced animals like goats has caused serious damage to cactus populations. In the Galápagos Islands, for example, grazing has had a significant impact on the local ecosystem.

Over-collection of cacti for sale has also had devastating effects on some species. In Mexico, the type locality of Pelecyphora strobiliformis was nearly denuded of plants due to over-collection.

Conservation of cacti can be done in situ or ex situ. In situ conservation involves preserving habitats through legal protection and the creation of protected areas like national parks and reserves.

Examples of protected areas in the United States include Big Bend National Park in Texas and Joshua Tree National Park in California. In Latin America, Parque Nacional del Pinacate in Sonora, Mexico, and Pan de Azúcar National Park in Chile are also protected areas.

Ex situ conservation aims to preserve plants and seeds outside their natural habitats, often with the intention of later reintroduction. Botanical gardens play a crucial role in ex situ conservation, such as the Desert Botanical Garden in Arizona, which stores cactus seeds in long-term storage.

Additional reading: Do Cactuses Have Seeds

The cactus family is nearly endemic to the New World, spanning from southern Canada to southern South America. There is an exception - one species occurs naturally in Africa, Sri Lanka, and Madagascar.

Cacti are most common in semiarid habitats with low rainfall, yet with dependable rainy seasons. This is where you'll find the highest numbers of both plants and species.

About 300 species occur in the Sonoran Desert region, which is just one example of the many habitats where cacti thrive.