Flowering plants, or angiosperms, now dominate the plant world, comprising 80% of land plants. Through a downsizing process, angiosperms have compact genomes, allowing for more cells, including important carbon dioxide-exchanging stomata. This enables more efficient photosynthesis and increased food production. When assessing angiosperms vs gymnosperms, angiosperms facilitate greater carbon dioxide-oxygen exchange. The downsizing that angiosperms underwent in their evolution has given them an advantage in nature and with their ecological significance.
If we went back 40 million years - to the Cretaceous Period - and took a look around at the type of plants that were most common, you would see a lot of needle-covered plants. Plants like pine trees, which are part of a group of plants that scientists call gymnosperms. During this period, needle-type plants were the most abundant type of plants on Earth. There were just a few flowering plants - or angiosperms - that were showing up at this time.
Jumping back in our time machine and returning to the present day, we see that those few flowering plants have taken over the planet – at least as far as plants go. Flowering plants are everywhere. They now make up 80% of all plants you see on land.
Where did all those flowering plants come from and how have they come to dominate the plant world?
It turns out that the answer is tied up in the cells for these two types of plants, gymnosperms and angiosperms, and their genomes. A genome is the set of DNA that holds the instructions for a living thing. That DNA is found in most of the cells in an organism.
Our modern day angiosperms have gone through a downsizing process to make their genomes more compact. This allows the plant to pack more cells into a smaller space, including some important cells called stomata. This word comes from the Greek for ‘mouth’, which makes sense. These cells are where plants pull in carbon dioxide and expel oxygen and water in a process called photosynthesis. This exchange of gasses is the opposite of what animals do when they breathe in O2 and expel CO2.
Okay, so if more cells can pack into a plant, what does that do? Well, it allows the plant to have more stomata and veins than needle-type plants. And that makes them much better at photosynthesis.. The more stomata, the more efficient and successful the plant, because it can exchange more carbon dioxide with oxygen and water. The plant can make more food in the form of sugars and with more veins it can transport more materials throughout the plant.
This turns out to be an example where downsizing has been a huge benefit. It benefits the angiosperm plants that have taken over the plant world. It also benefits animals, because these plants exchange more carbon dioxide for oxygen than the gymnosperm plants.
