Plants may not seem like the most interesting things around, but they are definitely useful. In this lesson, we will explore the basic classification of plants and the unique characteristics of each group.
Overview of Plants
We rely on plants for more than most people think. Not only do they provide a good source of food, but they also provide us with the oxygen we breathe and many of the vitamins and minerals our bodies require. Even if you do not love fruits and vegetables, the other foods you may eat – such as chicken, steak or even seafood – rely on plants to get their nutrients.
In this lesson, we will look at the different groups of plants. Before we do that, let’s review what a plant actually is.Plants are organisms that are photosynthetic, are eukaryotic and have cell walls. Part of this definition may make sense, but let’s look at it piece-by-piece in order to fully understand what defines a plant.Photosynthesis is the process by which autotrophs convert light energy into chemical energy. This is done when plants use energy from the sun, as well as other reactants such as carbon dioxide and water, to make sugar, most commonly glucose.
The balanced reaction for photosynthesis is 6CO2 + 6H2O + light energy -> C6H12O6 + 6O2, which is read as ‘carbon dioxide plus water plus light energy yields glucose plus oxygen.’ Plants store glucose as food and release the oxygen, which is then used by organisms such as humans.Eukaryotic means a cell with a nucleus and membrane-bound organelles. If you have learned about cells before, you may recall hearing about prokaryotic versus eukaryotic cells. Remember that prokaryotic cells do not have a nucleus or membrane-bound organelles. Eukaryotic cells are those that you generally think of because they are the cells that are in your body. These same cells are found in plants.
One key difference between the cells in your body and the cells in plants is the third part of the definition of plants: cell walls. A cell wall is a rigid layer around a cell.
Now that we have the definition of plants down, let’s look at how plants are classified. The first division of plants is seen in vascular tissue, or tissue used to transport water and nutrients throughout a plant.
Think of vascular tissue as the water lines in a city. These lines bring water to your home much like the vascular tissue of plants brings water to different parts of the plant. There are two types of vascular tissue: xylem and phloem. Xylem transports water and dissolved minerals, while phloem transports food. The easiest way to remember which vascular tissue is which is that ‘phloem’ and ‘food’ both start with the same sound.Plants that do not have xylem and phloem are considered nonvascular.
These plants are small, simple and less advanced than most plants that you may think of. Mosses, liverworts and hornworts are the three main groups of nonvascular plants. They are all small because there is no transport system to move required food and nutrients around in the plant. Also, these nonvascular plants do not have roots but instead have rhizoids, which are little hairs that help anchor the plant.
We will look at nonvascular plants a bit more in later lessons.Vascular plants have xylem and phloem and are probably what you think of when you think of plants. Common examples are trees, grasses and shrubs. Because of the vascular tissue, these plants can grow to be incredibly large as nutrients and water are moved from the roots to the leaves and anywhere else in the plant.
We will now look at types of vascular plants in greater detail.
Gymnosperm vs. Angiosperm
There are several ways to classify vascular plants.
The first grouping is based on the presence or absence of flowers. Gymnosperms were the first plants with seeds. They are vascular plants and do not produce flowers. However, the seed is beneficial because it provides protection and food for the plant embryo. Examples of gymnosperms include conifers – or evergreens – and ginkgoes.Angiosperms are plants with flowers.
They are more advanced than gymnosperms because of the presence of flowers. The flower is useful because it attracts organisms such as bees, bats and beetles to pollinate the flower, allowing the seed to be fertilized. Examples of angiosperms include roses, apple trees and magnolias. Just like there were different types of vascular plants, there are also different types of angiosperms.
Let’s look at these two subgroups next.
Monocot vs. Dicot
There are two categories of flowering plants based on the number of seed leaves.
Before we can look at these two groups, we first need to understand what a seed leaf is. The term that scientists use is cotyledon. This seed leaf is found in the seed and is the first leaf to grow on the new plant. We can see what a cotyledon looks like in this picture.
Angiosperms are categorized based on the number of cotyledons present. A flowering plant is either considered to be a monocot or a dicot. Let’s first look at monocots. Monocot is short for ‘monocotyledon,’ meaning ‘one seed leaf.’ These plants are simple flowering plants such as grasses, corn and palm trees.
Their flower petals are always in groups of three and their leaves are long. We can see these three distinctive characteristics in the picture below. You can note the single seed leaf, the three flower petals and the long leaves.
The other type of angiosperm is a dicot, which is short for ‘dicotyledon,’ meaning ‘two seed leaves.’ These plants are what you generally think of when you think of flowering plants. Examples of dicots include roses, sunflowers, cacti and apple trees.
Their flower petals are always in groups of four or five, and they have complex leaves with veins. We can see these three distinctive characteristics in the picture below. You can note the two seed leaves, the four or five flower petals and the complex leaves.
Plants are all around us, but we often overlook them. Plants are unique and important because they can create chemical energy from light energy through the process of photosynthesis. They have eukaryotic cells with cell walls made of cellulose.
We looked at several groups of plants, so let’s review all of these. We first looked at plants based on vascular tissue. Plants that have xylem – water-carrying tubes – and phloem – food-carrying tubes – are called vascular and are what you generally think of when you think of plants. Plants that do not have this transport system are called nonvascular and are small, simple plants such as mosses.We then looked at types of vascular plants based on the presence or absence of flowers. Gymnosperms are plants that have seeds but no flowers.
Examples of these are pine trees or conifers. More complex vascular plants do have flowers and are called angiosperms. We broke this group into two subgroups based on the number of cotyledon, or seed leaves. Monocots have only one seed leaf, flower petals in threes and long leaves.
Dicots have two seed leaves, flower petals in fours or fives and complex leaves with veins.Regardless of the classification of a plant, remember that all plants are vital to our survival because of the food and oxygen that they provide.
After this lesson, you will be able to explain how to classify plants into vascular versus nonvascular plants and monocots versus dicots.