Types Of Cactus: Taxonomy And Classification

Types Of Cactus: Taxonomy And Classification

For decades, researchers have tried to conclude a steady line of taxonomic history for cacti. As studies have opened and closed, only a few reliable classifications have been drawn until today. Understanding the types of cactus: taxonomy and classification further helps us comprehend the nature of their diversity.

In this article, we’ll be discussing the history behind classifying cacti and their taxonomic hierarchy, the categories within the taxonomic ranks of cacti, and the main subfamilies along with their distinct features.

History of Categorizing Cacti

The history of categorizing cacti is closely linked to the study of the phylogeny and evolution of cactus. It was not until 1984 with the formation of the International Cactaceae Systematics Group that the thorough classification of cacti actually began.

History of Categorizing Cacti

The objective of the group was to produce a reliable taxonomic history and classification of cacti down to their lowest level of biological hierarchy.

As the 21st century rolled in, it gave light to many research studies which were able to successfully classify about 130 genera of cacti and 1500 separate species, taking into consideration the morphology of cactus and their evolutionary relationships.

Afterward, these species and genera were categorized into subfamilies and tribes.

However, as the years passed, researchers discovered that these cacti had a plethora of different tribes, subfamilies, and genera that were monophyletic, meaning that they did not descend from a common ancestor.

To this day, experts in the field of phytogeography remain uncertain about the correct taxonomic evolution of cacti, stating that as studies continue, more changes appear in the hypothesized categories of cacti.

Basics of the Taxonomy of Cactus

The Cactaceae family is a diverse group of plants that includes over 1,500 different species. Cacti are found throughout the Americas, from Canada to Argentina.

The taxonomy of the Cactaceae family is complex and has changed over time. In this article, we will explore the current taxonomy of the Cactaceae family.

Here are the main taxonomic categories of cactus, with their definitions and overviews

Taxonomy of Cactus

Kingdom and Phylum

In the taxonomic hierarchy, a kingdom is one rank that is split into smaller divisions called phyla (plural of phylum). A kingdom is at the top of the taxonomic rank as it consists of the most general taxon in classifying cacti.

Cacti belong to the Plantae kingdom and the Tracheophyta phylum. Tracheophyta is a group of plants that have specialized tissues for conducting water and nutrients, such as the xylem and phloem.

The specialized tissues of Tracheophyta, combined with the unique adaptations for water conservation of cactus, make these plants highly adapted to harsh desert climates.

Class

This is the next taxonomic rank. It only consists of organisms that share the same attributes.

Cacti belong to the Magnoliopsida class, which is also known as the dicotyledons or dicots. Magnoliopsida is a class of flowering plants that have two embryonic leaves, or cotyledons, in their seeds.

Order

After the class comes order. But unlike class, the order is the taxonomic rank that categorizes organisms within the class by their similarities in characteristics and nature.

Cacti belong to the Caryophyllales order, which is a group of flowering plants that includes over 11,000 different species. The Caryophyllales order includes many different families of plants, such as Amaranthaceae, Cactaceae, and Polygonaceae.

Family

Before the last two taxonomic ranks (genus and species), family is the rank that classifies organisms according to order and genus. It usually consists of one or two genera that are defined by biological attributes such as gene family, protein family, and so on.

Cacti belong to the Cactaceae family, which is a group of succulent plants that are well-adapted to hot and dry environments. The Cactaceae family is divided into four subfamilies: Cactoideae, Maihuenioideae, Opuntioideae, and Pereskioideae.

Genus and Species

As mentioned before, the Cactaceae family includes over 130 genera and 1,500 different species. Each cactus species is classified based on its unique characteristics, such as stem shape, spines, and flower color.

Since so many species are prized for their beauty and rarity, cacti are often grown for cultivation as ornamental plants. However, the uses of cactus in early history stretched beyond their decoration.

The Four Main Subfamilies of Cactus

Even though the taxonomy and classification of cacti are always being debated, the ICSG has successfully categorized cacti into four primary subfamilies, which are yet to be refuted.

Here is a cladogram depicting the link between the subfamilies —

Four Main Subfamilies of Cactus 1

Subfamilies are the main categories in understanding the types of cactus: taxonomy and classification. Let’s look at each of these subfamilies individually.

1.   Cactoideae

It is the largest subfamily of the Cactaceae family and includes over 1,400 different species. This subfamily is characterized by its globular or columnar shape and its spiny stems.

Subfamilies of Cactus- Cactoideae

The distribution of cactus worldwide reveals that this subfamily is primarily found throughout the Americas, from Canada to Argentina. This subfamily also has the greatest number of tribes, which are sections within the subfamily.

There are about 9 known tribes with a huge variety of separate species. However, the validity of these tribes, along with their genera, has been debated.

In 2011, a study showed that the majority of the sampled 36 genera were not monophyletic, except for only two.

2.   Maihuenioideae

In comparison to Cactoideae, maihuenioideae is a small subfamily of the Cactaceae family that includes only two species. These cacti are found in the Andes Mountains of South America and are characterized by their small, cylindrical stems and lack of spines.

Subfamilies of Cactus- Maihuenioideae

The phylogenetic studies surrounding this subfamily is rapidly changing, resulting in very little and unreliable information about its monophyletic nature within the two species.

3.   Opuntioideae

Opuntioideae is a subfamily of the Cactaceae family that includes over 300 different species. This subfamily is characterized by its flat, paddle-shaped stems and clusters of spines. The reproductive ecology of cactus is also interesting in this subfamily.

Subfamilies of Cactus- Opuntioideae

Many species in the Opuntioideae have specialized reproductive structures, such as the fleshy fruits of the prickly pear cactus, which contain numerous seeds and are an important food source for many animals.

After cactoideae, this subfamily has the second greatest number of species diversity with around 5-6 known tribes.

It should also be noted that many of the genera within this subfamily are not monophyletic, for example, the most biologically diverse being the maihueniopsis which traces back to four different ancestors.

Also, the two numerous genera, cylindropuntia and optunia are not monophyletic.

4.   Pereskioideae

Pereskioideae is a small subfamily of the Cactaceae family that includes only one genus, Pereskia. These cacti are unique in that they have leaves, which is rare for cacti. Pereskia cacti are found in the Caribbean and South America.

Subfamilies of Cactus- Pereskioideae

Since there is only one genus, there is not any doubt surrounding the monophyletic nature of this subfamily.

The Nyffler and Eggli Classification

In 2010, two molecular phylogenetic researchers, Urs Eggli and Reto Nyffeler, drew a classification of cacti with all the information given at the time.

Their cladogram depicts a similar outline to Hern’s cladogram, which was drawn in 2011, with a few differences.

Nyffler and Eggli Classification

Nyffler and Eggli placed cacti genera into subfamilies and tribes in a categorized table, which can be viewed here. It’s a concise list of all tribes, subfamilies and genera in their systematic order, alongside older tribe names classified by the ICSG.

Conclusion

In summary, the types of cactus: taxonomy and classification are complex and rapidly evolving. As more studies come to the surface, more changes are made to the taxonomic details of cactus categories.

Each cactus species is categorized based on distinctive qualities. We can better appreciate and comprehend these intriguing plants if we have a better understanding of the taxonomy of the Cactaceae family.

References:

  • https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/
  • https://en.wikipedia.org/wiki/Cactus/

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