Learning about the many types of vascular plants is more important than you may think.
For instance, fiddlehead ferns all look alike to the untrained eye, but distinctive characteristics set apart a tasty ostrich fern from a bracken fern believed to contain carcinogens. Vascular plants have common – and in some cases peculiar – adaptations that provide an evolutionary advantage.
Definition of Vascular Plants
Vascular plants are “tube plants” called tracheophytes. Vascular tissue in plants is comprised of xylem, which are tubes involved in water transport, and phloem, which are tubular cells that distribute food to plant cells. Other defining characteristics include stems, roots and leaves.
Vascular plants are more complex than ancestral nonvascular plants. Vascular plants have a type of internal “plumbing” that transports products of photosynthesis, water, nutrients and gases. All types of vascular plants are terrestrial (land) plants not found in freshwater or saltwater biomes.
Vascular plants are also defined as eukaryotes, meaning they have a membrane-bound nucleus, which sets them apart from the prokaryotic bacteria and archaea. Vascular plants have photosynthetic pigments and cellulose to support cell walls. Like all plants, they are place-bound; they cannot flee when hungry herbivores come along looking for a meal.
How Are Vascular Plants Classified?
For centuries, scholars have used plant taxonomy, or classification systems, to identify, define and group plants. In ancient Greece, Aristotle’s method of classification was based on the complexity of organisms.
Humans were placed at the top of the “Great Chain of Being” just below angels and deities. Animals came next, and plants were relegated to lower links of the chain.
In the 18th century, Swedish botanist Carl Linnaeus recognized that a universal method of classification was needed for scientific study of plants and animals in the natural world. Linnaeus assigned each species a Latin binomial species and genus name.
He also grouped living organisms by kingdoms and orders. Vascular and nonvascular plants represent two large subgroups within the plant kingdom.
Vascular vs. Nonvascular Plants
Complex plants and animals need a vascular system to live. For instance, the vascular system of the human body includes arteries, veins and capillaries involved in metabolism and respiration. It took small primitive plants millions of years to develop vascular tissue and a vascular system.
Because ancient plants did not have a vascular system, their range was limited. Plants slowly evolved vascular tissue, phloem and xylem. Vascular plants are more prevalent today than nonvascular plants because vascularity offers an evolutionary advantage.
Evolution of Vascular Plants
The first fossil record of vascular plants dates back to a sporophyte called Cooksonia that lived about 425 million years ago during the Silurian Period. Because Cooksonia is extinct, studying the plant’s characteristics is limited to fossil record interpretations. Cooksonia had stems but no leaves or roots, although some species are believed to have developed vascular tissue for water transport.
Primitive nonvascular plants called bryophytes adapted to being land plants in areas where there was sufficient moisture. Plants such as liverworts and hornworts lack actual roots, leaves, stems, flowers or seeds.
For instance, whisk ferns are not true ferns because they merely have a leafless, photosynthetic stem that branches into sporangia for reproduction. Seedless vascular plants such as club mosses and horsetails came next in the Devonian Period.
Molecular data and fossil records show that seed-bearing gymnosperms such as pines, spruce and ginkgoes evolved millions of years before angiosperms like broad-leaf trees; the exact time span is debated.
Gymnosperms do not have flowers or bear fruit; seeds form on leaf surfaces or scales inside pine cones. By contrast, angiosperms have flowers and seeds enclosed in ovaries.
Characteristic Parts of Vascular Plants
Characteristic parts of vascular plants include roots, stems, leaves and vascular tissue (xylem and phloem). These highly specialized parts play a critical role in plant survival. The appearance of these structures in seed plants differs greatly by species and niche.
Roots: These reach from the stem of the plant into the ground in search of water and nutrients. They absorb and transport water, food and minerals via vascular tissues. Roots also keep plants stable and securely anchored against blowing winds that can topple trees.
Root systems are diverse and adapted to soil composition and moisture content. Taproots extend deep into the ground to reach water. Shallow root systems are better for areas where nutrients are concentrated in the upper layer of the soil. A few plants like epiphyte orchids grow on other plants and use air roots to absorb atmospheric water and nitrogen.
Xylem tissue: This has hollow tubes that transport water, nutrients and minerals. Movement occurs in one direction from the roots to the stem, leaves and all other parts of the plant. Xylem has rigid cell walls. Xylem can be preserved in the fossil record, which aids in identification of extinct plant species.
Phloem tissue: This transports the products of photosynthesis throughout plant cells. Leaves have cells with chloroplasts that use the sun's energy to make high-energy sugar molecules that are used for cell metabolism or stored as starch. Vascular plants make up the base of the energy pyramid. Sugar molecules in water are transported in both directions to distribute food as needed.
Leaves: These contain photosynthetic pigments that harness the sun’s energy. Broad leaves have a wide surface area for maximum exposure to sunlight. However, thin, narrow leaves covered with a waxy cuticle (a waxy outer layer) are more advantageous in arid areas where water loss is a problem during transpiration. Some leaf structures and stems have spines and thorns to warn off animals.
Leaves of a plant can be classified as microphylls or megaphylls. For instance, a pine needle or blade of grass is a single strand of vascular tissue called a microphyll. By contrast, megaphylls are leaves with branching veins or vascularity within the leaf. Examples include deciduous trees and leafy flowering plants.
Types of Vascular Plants With Examples
Vascular plants are grouped according to how they reproduce. Specifically, the various types of vascular plants are classified by whether they produce spores or seeds to make new plants. Vascular plants that reproduce by seed evolved highly specialized tissue that helped them spread across the land.
Spore producers: Vascular plants can reproduce by spores just as many nonvascular plants do. However, their vascularity makes them visibly different from more primitive spore-producing plants that lack that vascular tissue. Examples of vascular spore producers include ferns, horsetails and club mosses.
Seed producers: Vascular plants that reproduce by seed are further divided into the gymnosperms and angiosperms. Gymnosperms such as pine trees, fir, yew and cedars produce so-called “naked” seeds that are not enclosed in an ovary. The majority of flowering, fruit-bearing plants and trees are now angiosperms.
Examples of vascular seed producers include legumes, fruits, flowers, shrubs, fruit trees and maple trees.
Characteristics of Spore Producers
Vascular spore producers like horsetails reproduce through alteration of generations in their life cycle. During the diploid sporophyte stage, spores form on the underside of the spore-producing plant. The sporophyte plant releases spores that will become gametophytes if they land on a moist surface.
Gametophytes are small reproductive plants with male and female structures that produce haploid sperm that swim to the haploid egg in the female structure of the plant. Fertilization results in a diploid embryo that grows into a new diploid plant. Gametophytes typically grow close together, enabling cross-fertilization.
Reproductive cell division occurs by meiosis in a sporophyte, resulting in haploid spores that contain half as much genetic material at the parent plant. The spores divide by mitosis and mature into gametophytes, which are tiny plants that produce haploid egg and sperm by mitosis. When gametes unite, they form diploid zygotes that grow into sporophytes via mitosis.
For example, the dominant stage of life of the tropical fern – that big, beautiful plant that thrives in warm, wet places – is the diploid sporophyte. Ferns reproduce by forming unicellular haploid spores via meiosis on the underside of fronds. The wind widely disperses the lightweight spores.
Spores divide by mitosis, forming separate living plants called gametophytes that produce male and female gametes that merge and become tiny diploid zygotes that can grow into massive ferns by mitosis.
Characteristics of Vascular Seed Producers
Seed-producing vascular plants, a category that includes 80 percent of all plants on Earth, produce flowers and seeds with a protective covering. Many sexual and asexual reproductive strategies are possible. Pollinators can include wind, insects, birds and bats that transfer pollen grains from the anther (the male structure) of a flower to a stigma (the female structure).
In flowering plants, the gametophyte generation is a short-lived stage that takes place within the plant’s flowers. Plants can self-pollinate or cross-pollinate with other plants. Cross-pollination increases variation in the plant population. Pollen grains move through the pollen tube to the ovary where fertilization occurs, and a seed develops that may be encapsulated in a fruit.
For example, orchids, daisies and beans are the largest families of angiosperms. The seeds of many angiosperms grow within a protective, nourishing fruit or pulp. Pumpkins are edible fruit with delicious pulp and seeds, for instance.
Advantages of Plant Vascularity
Tracheophytes (vascular plants) are well-suited for the terrestrial environment unlike their ancestral marine cousins that could not live outside water. Vascular plant tissues offered evolutionary advantages over nonvascular land plants.
A vascular system gave rise to rich species diversification because vascular plants could adapt to fit changing environmental conditions. In fact, there are approximately 352,000 species of angiosperms of varying shapes and sizes covering the Earth.
Nonvascular plants typically grow close to the ground to access nutrients. Vascularity allows plants and trees to grow much taller because the vascular system provides a transport mechanism for actively distributing food, water and minerals throughout the plant body. Vascular tissue and a root system provide stability and a fortified structure that supports unparalleled height under optimal growing conditions.
Cacti have adaptive vascular systems to efficiently retain water and hydrate living cells of the plant. Huge trees in the rainforest are propped up by buttress roots at the base of their trunk that can grow to 15 feet. In addition to providing structural support, buttress roots increase surface area for absorbing nutrients.
Ecosystem Benefits of Vascularity
Vascular plants play a pivotal role in maintaining ecological balance. Life on Earth depends on plants to provide food and habitat. Plants sustain life by acting as carbon dioxide sinks and by releasing oxygen into the water and air. Conversely, deforestation and increased levels of pollution affect global climate, leading to loss of habitat and species extinction.
Fossil records suggest that redwoods – descended from conifers – have existed as a species since dinosaurs ruled the Earth during the Jurassic Period. The New York Post reported in January 2019 that, to mitigate the effects of greenhouse gases, an environmental group based in San Francisco planted redwood saplings cloned from ancient redwood stumps found in America that grew to 400 feet tall. According to the Post, these mature redwoods could remove over 250 tons of carbon dioxide.
- George Washington University: Trachelophytes – Vascular Plants
- University of California Museum of Paleontology: Carl Linnaeus (1707-1778)
- CK-12: Evolution of Vascular Plants – Advanced
- U.S. Forest Service: Fern Reproduction
- Cal Tech: Buttress Roots
- The New York Post: Cloned Ancient Redwood Trees Could Be the Key to Fighting Climate Change
- The Plant List: The Angiosperms (Flowering Plants)
- CK-12: Taxonomic Categories
- Alaska Plant Materials Center: Fiddlehead Ferns