My Science School

For a long time, scientists have assumed that plants became more complex as seeds and flowers made their way. A new study has revealed that this actually happened in two bursts with a long period stasis in between.

The study, led by researchers at Stanford University, reveals that evolution in land plants didn't take place gradually over hundreds of millions of years. Instead, land plants had two dramatic bursts nearly 250 million years apart. After the first one occurred early in plant history and gave rise to the development of seeds, there was a long lull in between before the second burst, which saw the diversification of flowering plants.

The difference in complexity between flowering plants and non-flowering plants is so stark that botanists have long focussed on characteristics within these groups and studying their evolution separately. This is because flowers are more diverse and intricate than anything else in plants.

A flowery problem

To overcome these differences, the researchers in this study designed a system that classified the number of different parts in the plants reproductive structures. This was done based on observation alone and then each species was scored based on how many types of parts it has and the degree to which it exhibited clustering. The researchers were able to categorise 1.300 land species from about 420 million years ago until the present.

250-million-year hiatus

Based on this technique, the researchers were able to show that land plants first diversified about 420 million to 360 million years ago with the onset of early seed plants. And even though insect pollination and animal seed dispersal might have appeared as early as 300 million years ago, it was only about 100 million years ago that the complexity of flowering plants came about The unique nature of flowering plants meant that the second burst of evolution was much more dramatic than the first.

Thus, by using a simple but novel metric, plants were classified based on the arrangement and number of parts in their reproductive system. Once that was achieved, the researchers were able to show that between the initial evolution of seeds and the total change that happened with flowering plants, there was a period of stasis that extended for nearly 250 million years when there was hardly any change. These findings were published in Science in September 2021 and offer insights into the timing and magnitude of these changes.

Picture Credit : Google

Plants, animals and even microbes that live on coral reefs have evolved a rich variety of defense strategies to protect themselves from predators. Some have physical defenses like spines and camouflage. Others have specialized behaviors – like a squid expelling ink – that allow them to escape. Soft-bodied or immobile organisms, like sponges, algae and sea squirts, often defend themselves with noxious chemicals that taste bad or are toxic.

Some animals that can’t manufacture their own chemical weapons feed on toxic organisms and steal their chemical defenses, having evolved resistance to them. One animal that does this is a sea slug that lives on the reefs surrounding Hawaii and dines on toxic Bryopsis algae. Marine scientists suspected the toxin is made by a bacterium that lives within the alga but have only just discovered the species responsible and teased apart the complex relationship between slug, seaweed and microbe.

Ultimately, noxious chemicals allow predators and prey to coexist on coral reefs, increasing their diversity. This is important because diverse ecosystems are more stable and resilient. A greater understanding of the drivers of diversity will aid in reef management and conservation.

As marine scientists, we too study chemical defenses in the ocean. Our laboratory group at the Georgia Institute of Technology explores how marine organisms use chemical signaling to solve critical problems of competition, disease, predation and reproduction. That’s why we were particularly excited by the discovery of this new bacterial species.

The discovery of a symbiosis between a bacterium and a seaweed to produce a chemical defense is noteworthy. There are many examples of bacteria living inside the cells of invertebrate animals (like sponges) and manufacturing toxic chemicals, but a partnership involving a bacterium living in the cells of a marine seaweed to produce a toxin is unusual.

The finding adds a new dimension to our understanding of the types of ecological relationships that produce the chemicals shaping coral reef ecosystems.

Credit : The Conversation 

Picture Credit : Google

Poison ivy is a common poisonous plant that causes an itchy skin rash. Other rash-inducing poisonous plants include poison oak and poison sumac. These plants produce an oily sap called urushiol that brings on an irritating, itchy allergic reaction. When you touch a poisonous plant or an object that’s been in contact with a plant, you develop an itchy rash. This rash is a form of allergic contact dermatitis.

Poison ivy is most known for its leaves. Each leaf has three leaflets. A popular saying is, “Leaves of three, let them be.” Poison ivy grows as a shrub and a vine. Its summer-green leaves turn reddish in the spring and yellow, orange or red in the fall. A poison ivy shrub may have white berries.

The leaves have three leaflets like poison ivy, but with rounded tips. The leaves’ undersides are fuzzy and lighter in color than the top. Poison oak grows as a shrub. It’s most common in the western United States. The shrub sometimes has white or yellow berries.

Poison sumac is tall shrub or small tree has drooping clusters of green berries. (Nonpoisonous sumacs have red, upright berries. Contact with nonpoisonous sumacs won’t cause an allergic rash.) Each leaf has clusters of seven to 13 smooth leaflets arranged in pairs. Poison sumac thrives in wet, swampy regions.

Credit : Cleveland Clinic

Picture Credit : Google