Asterales

Asterales is a large order of flowering plants known as dicotyledonous plants. This group is very important because it contains the massive Asteraceae family. Asteraceae is famous for its composite flowers, which are made of many tiny florets. These florets work together to look like a single flower with many petals. While many plants have separate petals, Asterales often use this combined structure. This order is cosmopolitan, meaning these plants live all over the world. You can find them in hot deserts and even in very cold, frigid zones.

These plants share specific biological traits called synapomorphies. One major trait is how they store energy. Instead of using starch, they use a nutrient storage molecule called inulin. Another unique feature involves their stamen morphology, which is the shape of their pollen-producing parts. The stamens are usually found around the style, which is the part of the flower that receives pollen. They may be bunched together or fused into a single tube. This shape likely helps with a specific type of pollination. In this process, pollen is collected and stored along the length of the pistil, acting like a brush or plunger.

There are 11 different families within the Asterales order. The Asteraceae is the largest family, containing about 25,000 different species. The second largest family is the Campanulaceae, also known as bellflowers, which has about 2,000 species. The other nine families are much smaller, with fewer than 1,500 species combined. Most of these smaller families are found in Australia or South America. However, the two largest families are cosmopolitan and appear in many places. Many species of these large families are especially common in the Northern Hemisphere.

Scientists have used different systems to classify these plants over the years. The name Asterales has been used since at least 1926 in the Hutchinson system. In that older system, the order only contained five families. The Cronquist system previously listed Asteraceae as the only family in the group. Modern systems, such as APG II and APG III, have expanded the order to include 11 families. Another scientist, Rolf Dahlgren, placed the Asterales in a group called the superorder Asteriflorae. These changing systems help scientists better understand how plants are related.

The history of Asterales goes back millions of years. They are part of the angiosperms, or flowering plants, which appeared about 140 million years ago. The Asterales likely originated during the Cretaceous period. This was a time between 145 and 66 million years ago. They may have first appeared on the supercontinent Gondwana. This landmass eventually broke apart to form Australia, South America, Africa, India, and Antarctica. Because many families are found in the Southern Hemisphere, scientists believe the group had a southern origin.

Finding exact dates for the origin of Asterales is difficult because fossils are rare. Some estimates suggest the order began between 116 and 82 million years ago. Molecular clock calculations suggest the lineage split from other plants about 112 or 94 million years ago. We do have some very old evidence, though. Scientists have found Oligocene pollen from about 29 million years ago. They have also found seeds from the Oligocene and Miocene periods. These fossils belong to families like Menyanthaceae and Campanulaceae.

Asterales are very useful to humans in many ways. Many species are grown as food, such as lettuce, chicory, and the sunflower. Other plants in this order are used as spices or in traditional medicines. For example, the genus Chrysanthemum provides pyrethrum. This is a natural insecticide that has a minimal impact on the environment. Another plant, wormwood, is used to flavor a bitter European liquor called absinthe. These plants show how closely connected the natural world is to our daily lives.