All plants have systems to help them survive in their environment. But, these systems can vary quite a bit, depending on whether the plants are vascular or nonvascular. One of the biggest differences between these types of plants is that vascular plants have more complex systems.
Vascular plants grow taller than their nonvascular companions because they have complicated systems that enable them to absorb more water and nutrients from their environment than nonvascular plants, therefore encouraging their growth.
In this article, I’ll explore why vascular plants grow taller than nonvascular plants and what you need to know about the differences between these plants that affect their growth. Keep reading to learn more about why vascular plants grow taller than nonvascular plants.
Why Plants With Vascular Tissue Grow Taller
Vascular plants are a large group of plants you’ve seen in various places worldwide and probably in your garden too. That’s because approximately 80% of plants are vascular.
Examples of vascular plants include:
These plants have vascular tissues that transport fluid throughout them. To achieve this, they’re equipped with two types of tissues that enable the plants to grow tall without drying out, giving them a distinct advantage over nonvascular plants.
The two vascular tissues found in vascular plants are xylem and phloem:
Xylem is a tissue that transports water and dissolved minerals from the roots of the plant all the way up to its stems and leaves. It has thick, impenetrable walls that are waterproof and strong.
Xylem is mainly made out of a protein called lignin and dead cells. These ensure water and nutrients from the plant’s roots can be transported to the leaves.
Here’s how water moves through the plant via the xylem:
- Water gets absorbed by the plant’s roots.
- It moves into the xylem and produces upward pressure.
- Once the water reaches the plant’s leaves, water is used by the plant and evaporates through the stomata or pores.
- These pores transpire and push upward on the column of water in the xylem.
- The water moves up through the xylem via the processes of adhesion when water molecules cling to the xylem and cohesion when the molecules are drawn to each other.
Phloem is a plant tissue that transports food from the plant’s photosynthetic cells to other parts of the plant where they can be stored and used for growth. They basically transport food that’s been synthesized by the plant leaves down through the stem.
Phloem comprises specialized cells called sieve elements, phloem fibers, and phloem parenchyma cells.
- Sieve elements or tubes: These are columns of cells that have perforations in their walls. They provide the main channels for food to move throughout the plant.
- Phloem fibers: These are long cells that provide strength to the phloem tissues.
- Phloem parenchyma: These are also known as transfer cells and function to transport food.
The xylem and phloem tissues make up a complicated structure known as the vascular bundle. This is one of the first true structural support systems found in plants, and it enabled roots, leaves, and stems to form.
Vascular vs. Nonvascular Plants: Growth Differences
Nonvascular plants include types of moss, liverworts, and hornworts. Besides their lack of complex plant tissues and vascular bundles, they have important differences compared to vascular plants, which affect their growth.
Plants Need Specialized Tissue for Growth
Vascular plants have specialized stems, roots, and leaves, as well as a lignified xylem. Lignin is the material in the plants’ walls that makes them durable and waterproof, enabling the transportation of water and nutrients to various parts of the plant. By comparison, nonvascular plants don’t have any specialized tissues or any lignified xylem.
Vascular plants have two main organ systems that nonvascular plants lack:
A shoot system is made up of leaves, stems, and the plant’s reproductive parts – its fruits and flowers. This system grows above the ground to absorb UV light and use it for photosynthesis for the plant to grow.
A root system supports the plant and works to absorb nutrients and water underground. While most roots are located underground, some plants have roots that sprout out of the ground, known as adventitious roots.
Thick Cuticles Are Necessary for Sufficient Moisture
Vascular plants have cuticles, which are waxy layers or films that cover their leaves and prevent them from drying out. Cuticles, therefore, decrease water loss from the leaf surface.
By comparison, nonvascular plants don’t have special tissues to prevent water loss. This is why they cannot survive in many environments.
Some nonvascular plants do have cuticles, but they’re thin. As a result of a lack of thick cuticles, nonvascular plants are forced to remain close to the ground to ensure that they can get enough water from their environment.
Water And Nutrient Distribution Determines Height
Vascular plants are built with vascular systems, while nonvascular plants aren’t. This system is a network of tissues that connect all organs and transport water, nutrients, minerals, and organic molecules throughout the body of the plant.
Without such a complex system of tissues, nonvascular plants can’t ensure that their water and nutrients can be transported to all the parts of the plants. This keeps them shorter than vascular plants.
A Lack of Roots, Leaves, or Stems Makes Plants Shorter
As a result of their complex vascular systems, vascular plants grow roots, leaves, and stems. By comparison, nonvascular plants don’t have roots, leaves, or stems.
Here’s what nonvascular plants have instead:
- Leafy structures that aren’t proper leaves: They have what’s known as phyllids that look like leaves but only consist of a single sheet of cells, and absorb water.
- Hairy rhizoids instead of roots: These support the plant but don’t absorb water.
- Structures instead of stems: Some nonvascular plants have central structures that are a bit like stems, such as in the case of moss.
Simpler Water Diffusion Systems Make Plants Grow Shorter
Vascular plants are homoiohydric, which means that they can draw water from their environment via their root system, and they can regulate their water concentration. In comparison, nonvascular plants are poikilohydric, which means they don’t have systems to protect the plants against desiccation.
As a result of pulling water from their environment, vascular plants are capable of living in many different types of environments. In comparison, a lack of essential tissues and roots that can draw water from the soil means that nonvascular plants can only grow in shady and damp environments. Although the plants need water to complete their life cycles, their lack of vascular tissues means that they can’t regulate their water requirements.
Earlier in this article, we looked at how vascular plants are able to draw water from their environment, but nonvascular plants do this in a very different way. Nonvascular plants don’t have any channels that carry minerals and water. Instead, they have leaflike scales that absorb minerals and water.
Since they don’t transport food and water through the body of the plant, as in the case of vascular systems, nonvascular plants can’t grow very tall. They need to have direct contact with water in order to survive.
Although nonvascular plants have rhizoids instead of roots, these are simple structures that are essentially root-like hairs. They absorb water from the ground, then move it through the plant via diffusion and active transport.
Diffusion is when water is moved away from an area in which it’s highly concentrated, transporting it to cells that are empty and need it. This process requires no energy.
Active transport does require energy. It’s used by plants when they have to concentrate a substance in one place. It makes use of carrier protein molecules that carry the water or food from one side of the plant’s cell membrane to another that requires it.
Both of these methods are simple instead of advanced, which means that nonvascular plants need to remain in humid, wet environments in order to survive.
Evolution of Vascular Systems in Plants
Since they had a small size and lacked specialized systems, nonvascular plants were the first plants to exist. The first nonvascular plants that evolved were liverworts, after which hornworts and mosses came about.
Vascular plants developed from nonvascular plants. Over time, vascular plants gained their advanced plant systems. This system has enabled them to grow larger and adapt to a variety of environments.
Vascular plants and nonvascular plants are quite different. One of the biggest differences is that vascular plants grow larger than nonvascular plants, largely due to having far more complex systems
Some of the reasons why vascular plants grow larger than nonvascular plants are:
- Having xylem and phloem tissue which transport minerals and water throughout the plant
- Having thick cuticles that prevent desiccation
- Growing stems, roots, and leaves that work together to keep the plant healthy
- Being homoiohydric, which means they can draw water from their environment