Angiosperm Phylogeny Group facts for kids

Evolution of flowering plants according to the Angiosperm Phylogeny Group (2013)

The Angiosperm Phylogeny Group (APG) is a group of plant scientists from around the world. They work together to create a shared way of classifying flowering plants. This classification uses new information about how plants are related. This information comes from studying their genetic history.

Since 1998, the APG has released four main versions of their classification system. These were published in 1998, 2003, 2009, and 2016. The group wanted to fix older classification systems. These older systems did not group plants based on their true family trees. They often didn't include all the descendants of a common ancestor.

The APG's ideas are becoming very important. Many large plant collections, called herbaria, are now organizing their plants using the latest APG system.

Understanding Flowering Plant Classification

In the past, one scientist or a small group usually created plant classification systems. This led to many different systems around the world. For example, the Engler system was popular in Europe. The Bentham & Hooker system was used in Britain.

Before scientists had genetic evidence, flowering plants were classified in other ways. They looked at the plant's morphology (its physical shape, especially its flowers). They also studied its biochemistry (the chemicals inside the plant).

After the 1980s, new genetic evidence became available. Scientists used phylogenetic methods to study this evidence. This new information confirmed some old ideas about plant relationships. But it also completely changed many others. This rapid increase in knowledge caused many proposed changes. It made classification less stable for a while.

A big study in 1993 used genetic information from 5,000 flowering plants. This study led to some surprising results. For example, it showed that "dicotyledons" were not a single, distinct group. At first, scientists were careful about creating a whole new system based on just one study. However, later research continued to support these new findings.

Many scientists worked together on these studies. Instead of naming every person, they decided to call the new classification the Angiosperm Phylogeny Group classification, or APG. The first APG paper came out in 1998. It got a lot of attention. The goal was to create a widely accepted and more stable way to classify flowering plants.

As of 2016, the APG has published three updates: APG II (2003), APG III (2009), and APG IV (2016). Each new version replaced the older one. Many researchers have been involved in writing and contributing to these papers.

Classifications are like snapshots in time. They show what we know based on current research. Scientists, including APG members, keep publishing new ideas. So, classifications can change, even if it's sometimes inconvenient. However, the APG publications are now seen as a very reliable source. Here are some examples of their influence:

• Major herbaria, like Kew, are changing how they arrange their plant collections. They now follow the APG system.
• The important World Checklist of Selected Plant Families is being updated to the APG III system.
• In the US, a large photographic survey of plants uses the APG II system.
• In the UK, the standard guide to British plants (by Stace) now uses the APG III system.

Main Ideas of the APG System

The APG set out its main ideas for classification in its first paper in 1998. These ideas have stayed the same in all later updates. Here are the key principles:

• The traditional Linnean system of orders and families should be kept. The family is seen as very important for classifying flowering plants.
• Groups should be monophyletic. This means they must include all the descendants of a common ancestor. Older systems were rejected because they didn't follow this rule.
• The APG prefers to define groups like orders and families broadly. They believe a smaller number of larger orders is more useful. They try to avoid families with only one genus or orders with only one family. This is done as long as it doesn't break the rule of monophyly.
• Above orders and families, the term clades is used more freely. A clade is a group of organisms that includes an ancestor and all its descendants. The authors say it's not necessary to name every clade. But scientists need to agree on names for some clades, especially orders and families. This helps them communicate and discuss plants.

APG I (1998): The First Step

The first APG paper in 1998 was a big deal. It was the first time a large group of organisms was classified mainly using genetic features. The paper explained that existing classifications were "outdated." This was because they were not phylogenetic. They were not based on strictly monophyletic groups.

The APG I system proposed 40 orders of flowering plants. This was much fewer than the 232 orders in Takhtajan's 1997 classification. In 1998, only a few families had been studied in detail. The main goal was to agree on the names of higher orders. This agreement was relatively easy to reach.

Other features of the APG I classification included:

• Formal scientific names were not used above the order level. Instead, named clades were used. For example, eudicots and monocots were not given a formal rank.
• Many plant groups whose classification was unclear now found a place. However, 25 families still had an "uncertain position."
• The system offered alternative classifications for some groups. For example, the Fumariaceae family could be seen as separate or as part of Papaveraceae.

A major outcome was the change to the traditional division of flowering plants into two groups: monocots and dicots. Monocots were recognized as a true clade. But dicots were not. Many former dicots were placed in separate groups. These groups were seen as more "basal" (older) than both monocots and the remaining dicots (called eudicots).

APG II (2003): Focusing on Families

As the overall relationships between flowering plant groups became clearer, the APG focused on the family level. This included families that were known to be difficult to classify. The second APG paper in 2003 updated the 1998 classification. Changes were made only when there was "substantial new evidence."

The APG II system continued to group plants broadly. For example, it tried to place small families with only one genus into a larger group. The authors generally accepted the views of specialists. But they noted that specialists often prefer to "split" groups that look too different.

APG II also continued to use "bracketed" taxa. This allowed scientists to choose between a large family or several smaller ones. For example, the large family Asparagaceae included seven "bracketed" families. These could be seen as part of Asparagaceae or as separate families.

Some main changes in APG II were:

• New orders were proposed, especially for the "basal clades" that were just families before.
• Many previously unplaced families were now located within the system.
• Several major families were reorganized.

In 2007, a paper was published that listed the APG II families in a linear order. This was useful for organizing plant specimens in herbaria.

APG III (2009): Fewer Families, More Clarity

The third APG paper updated the 2003 system. The main structure of the system stayed the same. However, the number of previously unplaced families and genera was greatly reduced. This meant recognizing new orders and families. The number of orders increased from 45 to 59. Only 10 families were not placed in an order. Only two of these (Apodanthaceae and Cynomoriaceae) were left completely outside the classification.

A major change in APG III was ending the use of "bracketed" families. Instead, they favored larger, more inclusive families. As a result, the APG III system had only 415 families, down from 457 in APG II. For example, the agave family (Agavaceae) and the hyacinth family (Hyacinthaceae) were no longer seen as separate. They became part of the broader asparagus family (Asparagaceae).

The authors hoped this classification would not need many more changes. They said that alternative classifications, like in APG I and II, could cause confusion. Major herbaria rearranging their collections agreed to use the more inclusive families. This approach is now widely used in plant collections.

Two related papers were published at the same time. One gave a linear order for APG III families. The other gave, for the first time, formal taxonomic ranks for families in APG III. Before, only informal clade names were used above the order level.

APG IV (2016): Latest Updates

Developing the fourth version involved some debate. Reaching a consensus was harder than before. Scientists made more progress by using large amounts of genetic information. This included genes from different parts of plant cells.

The fourth version was finally published in 2016. It came from an international meeting and an online survey of botanists. The main structure of the system remains the same. But several new orders are included, such as Boraginales and Dilleniales. Some new families are recognized, like Kewaceae and Macarthuriaceae. Also, some previously separate families are now grouped together. For example, Aristolochiaceae now includes Lactoridaceae and Hydnoraceae.

Due to naming rules, the family name Asphodelaceae is used instead of Xanthorrhoeaceae. And Francoaceae is used instead of Melianthaceae. This brings the total number of orders to 64 and families to 416 in the APG system. APG IV also uses a linear approach for ordering families.

Keeping Up with Updates

Peter Stevens, one of the authors of all four APG papers, runs a website called the Angiosperm Phylogeny Website (APWeb). It's hosted by the Missouri Botanical Garden. This website has been updated regularly since 2001. It's a great place to find the latest research on flowering plant relationships that follows the APG approach. Other helpful resources include the Angiosperm Phylogeny Poster and The Flowering Plants Handbook.

Members of the APG

a = listed as an author; c = listed as a contributor

See also

In Spanish: Grupo para la filogenia de las angiospermas para niños