What are Angiosperms?
Angiosperm are flowering plants that are classified based on characteristics that include (but are not limited to) cotyledon structure, pollen grains, as well as flower and vascular tissue arrangement. Angiosperms are the dominant form of plant life in most terrestrial ecosystems, comprising about 90 percent of all plant species. Most crops and ornamental plants are angiosperms. Their success comes from two innovative structures that protect reproduction from variability in the environment: the flower and the fruit.
Due to the presence of flowers and enclosed seeds, they are called the phanerogams. Scientifically speaking, in these plants, the seeds are enclosed, with the ovules present in a hollow ovary.
The angiosperm life cycle is dominated by the sporophyte stage. Double fertilization is an event unique to angiosperms. One sperm in the pollen fertilizes the egg, forming a diploid zygote, while the other combines with the two polar nuclei, forming a triploid cell that develops into a food storage tissue called the endosperm.
Angiosperms are classified in a single phylum: the Anthophyta. Modern angiosperms appear to be a monophyletic group, which means that they originated from a single ancestor.
Flowering plants are divided into two major groups according to the structure of the cotyledons and pollen grains, among others. Monocots include grasses and lilies while eudicots or dicots form a polyphyletic group. However, many species exhibit characteristics that belong to either group; as such, the classification of a plant as a monocot or a eudicot is not always clearly evident.
Basal angiosperms are a group of plants that are believed to have branched off before the separation into monocots and eudicots because they exhibit traits from both groups. They are categorized separately in many classification schemes. The Magnoliidae (magnolia trees, laurels, and water lilies) and the Piperaceae (peppers) belong to the basal angiosperm group.
What are Gymnosperms?
Gymnosperms are flowerless plants that produce cones and seeds. The term gymnosperm literally means “naked seed,” as gymnosperm seeds are not encased within an ovary. Rather, they sit exposed on the surface of leaf-like structures called bracts.
Gymnosperms are vascular plants of the subkingdom Embyophyta and include conifers, cycads, ginkgoes, and gnetophytes. Some of the most recognizable examples of these woody shrubs and trees include pines, spruces, firs, and ginkgoes. Gymnosperms are abundant in temperate forest and boreal forest biomes with species that can tolerate moist or dry conditions.
Unlike angiosperms, gymnosperms do not produce flowers or fruit. They are believed to be the first vascular plants to inhabit land appearing in the Triassic Period around 245-208 million years ago. The development of a vascular system capable of transporting water throughout the plant enabled gymnosperm land colonization.
In the gymnosperm life cycle, plants alternate between a sexual phase and an asexual phase. This type of life cycle is known as alternation of generations. Gamete production occurs in the sexual phase or gametophyte generation of the cycle. Spores are produced in the asexual phase or sporophyte generation. Unlike in non-vascular plants, the dominant phase of the plant life cycle for vascular plants is the sporophtye generation.
Today, there are over one thousand species of gymnosperms belonging to four main divisions: Coniferophyta, Cycadophyta, Ginkgophyta and Gnetophya.
- Conifers are the dominant plant of the gymnosperms, having needle-like leaves and living in areas where the weather is cold and dry.
- Cycads live in warm climates, have large, compound leaves, and are unusual in that they are pollinated by beetles rather than wind.
- Gingko biloba is the only remaining species of the Gingkophyta and is usually resistant to pollution.
- Gnetophytes are the gymnosperms believed to be most closely related to the angiosperms because of the presence of vessel elements within their stems.
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Angiosperms vs Gymnosperms
| Elements of Comparison | Gymnosperms | Angiosperms |
| Meaning | Gymnosperms are seed producing, non-flowering plants whose seeds are exposed and not enclosed in an ovule. | Angiosperms are seed-producing, flowering plants whose seeds are enclosed within an ovary. |
| Examples | Examples of gymnosperms include pine, conifers, cycads, Gnetophytes, Ginko, spruce, cactus, fir. | Examples of angiosperms include roses, peas, grains, lettuce, lilies, daffodils, sunflowers, maples, orchids. |
| Process of pollination | Mainly rely on the wind for the process of pollination. | Mainly rely on the insects for the process of pollination. |
| Root system | Many of gymnosperms possess taproot system. | Angiosperm plants possess not only taproot but also various roots and stem modification. |
| Type of Branches | Possess two types of branches i.e long shoots and dwarf shoots collectively referred to as spur. | Possesses only one type of branches. |
| Endosperm | E`ndosperm is derived from female gamytophyte and therefore, a haploid is formed. | Endosperm is derived from fertilization of sperm nucleus with two polar nuclei and therefore a triploid is formed. |
| Stomata | Possess true stomata. | Possess sunken stomata |
| Flowers | Do not possess flowers instead they possess cones. | Possess flowers. |
| Vessels | Majority of gymnosperms lack vessels for conducting water except for the phylum gnetophyta which has vessels. | Angiosperms on the other hand, have vessels for conducting water. |
| Companion Cell | Lack companion cells in phloem tissue. | Have companion cells in phloem tissue. |
| Fertilization | One fertilization occurs in the ovules and result in formation of a zygote (2n). | Double fertilization occurs and results in formation of zygote (2n) and endosperm (3n). |
| Leaves | The leaves of gymnosperms are cone bearing or needle like. | The leaves of angiosperms are flat. |
| Gametophyte structures | The male and female gametophyte structures are present on separate male and female cones in gymnosperms. | The male and female gametophyte structures in angiosperms are part of the flower. |
| Life cycle | The life cycle of gymnosperms is characterized by alternation of generations. | Angiosperms life cycle is dominated by the sporophyte generation. |
| Alternative Name | The gymnosperms are known as softwood as they have the ability to last during the winter. | The angiosperms are known as hardwood and usually change color during summer a die. |
| Mature Pollen | Mature pollen grains consist of three cells, that is, one tube cell and two sperm cells. | Has a mature pollen grain consisting of two sperm nuclei. |
| Nuclei | Mature gametophyte contains 2-3 archegonia which contain large egg nucleus. | Embryo sac of a mature megagametophyte consists of 7 cells, with a total of 8 nuclei. |
| Archegonia | Archegonia are present in the mature gametophyte. | There are no archegonia in mature megagametophyte. |
Also Read: Difference Between Evergreen And Deciduous Trees
Key Points
- Gymnosperms are older than angiosperms on the evolutionary scale. They are found far earlier in the fossil record than angiosperms.
- Gymnosperms produce both male and female cones, each making the gametes needed for fertilization; this makes them heterosporous.
- Megaspores made in cones develop into the female gametophytes inside the ovules of gymnosperms, while pollen grains develop from cones that produce microspores.
- The term “gymnosperm” literally means “naked seed.” This is because the seeds produced by gymnosperms are not encased in an ovary. Instead, gymnosperm seeds sit exposed on the surface of leaf-like structures called bracts.
- With the exception of extreme habitats, angiosperms populate every land biome and aquatic community. They are a major food source for animals and humans, and are a major economic source for the production of various commercial products.
- Two types of angiosperms are woody and herbaceous plants. Woody plants include trees and some shrubs. Herbaceous plants include beans and corn.
- Gymnosperms are often found in temperate forest and boreal forest biomes.