The kingdom Plantae is in the domain of Eukarya, which means that all plants are eukaryotes with eukaryotic cells. Organisms within the kingdom Plantae are also defined and classified as having chlorophyll, having cellulose in their cell walls and not moving on their own accord.
However, the classifications don't stop there. Plants are further classified into subgroups based on their makeup and how they reproduce.
How they reproduce is divided into two general classes: seed bearing and non-seed bearing. The seed-bearing plants are then divided into angiosperms and gymnosperms.
The first split in plant classification is whether plants have vascular systems (a.k.a. vascular plants) and those that do not have vascular systems. From there, vascular plants are split into two groups based on their reproductive structures: seed plants and non-seed bearing plants.
Those that don't make seeds are plants like:
Seed plants are the other category that can be further broken down into what types of seeds they create and how those seeds are housed. The great majority of vascular plant species (about 94 percent) are what's known as angiosperms, which are flowering plants that house seeds in fruit or flowers.
The other group of seed bearing plants are called gymnosperms.
Gymnosperms are vascular land plants that use seeds as their reproductive structures with those seeds appearing as "bare" or "naked seeds." This means that unlike in flowering or fruiting angiosperms, the reproductive structures on gymnosperms are not encased in a protective ovary. They're literally "naked" and are usually found in cones.
Scientists have used the fossil record to create a timeline of the evolution of gymnosperms. They believe that seed ferns evolved first around 400 million years ago. It's from these seed ferns that gymnosperms arose.
The first evidence of gymnosperms arose during the middle Devonian Period in the Paleozoic Era around 390 million years ago. After the plants' initial evolution, the Permian Period brought drier conditions. This gave seed plants like the newly evolved gymnosperms an evolutionary edge over other non-seed bearing plants, which allowed them to rapidly spread and diversify.
While gymnosperms continued to dominate the Earth throughout the Mesozoic Era, angiosperms arose and quickly overtook gymnosperms as the dominant plants after the angiosperms evolved around 125 million years ago.
Most gymnosperm species have some or all of the following qualities (along with their lack of flowers/fruit):
The life cycle of a common gymnosperm, a conifer, is an example of a general gymnosperm life cycle. While this life cycle can be generalized to most gymnosperms, not all gymnosperms use cones. However, since a great majority do, that is the example most commonly used.
Sporophyte and gametophyte phases. Similar to other plants, gymnosperms reproduce via an alternation of generations. This means that there are two distinct phases that alternate: the spore-bearing phase (sporophyte) and the gamete-bearing phase (gametophyte). In gymnosperms, the sporophyte phase lasts longer; in other words, the plant is most often in the sporophyte phase.
Adult sporophyte plants that bear both the diploid male cones and the diploid female/ovulate cones on the same plant are referred to as monoecious plants. Some gymnosperms, however, make only one of those types of cones on each plant. Those are called dioecious plants.
Male/pollen cones are usually smaller than female/ovulate cones. Pollen cones are also usually lower to the ground than ovulate cones when they're on the same plant. Each of the cone types have sporophylls, which are leaves that contain spores. Male cones have microspores while female cones have megaspores.
To put it a bit more simply, cones and cells in the gametophyte phase grow and are displayed on a mature and fully formed sporophyte-phase plant.
Gamete creation. It's from those two spore types that haploid gametes are produced via meiosis. When this occurs, those gametes/cones that they are in, are in the gametophyte phase. During the male/female gametophyte phase, haploid gamete cells are produced by both cones to create sperm/pollen grains in the male cones from the microspores, and eggs in the ovulate cones from the megaspores.
Reproduction and fertilization. Gymnosperms are unique from angiosperms in their pollination process in that they depend almost solely on wind and other natural phenomena in order to disperse pollen and fertilize eggs. Sometimes insects can act as pollinators as well. While pollen is dispersed via wind, the eggs stay attached to the plant until fertilized.
When the pollen grains reach the appropriate ovulate cone, the female cone will often "close up." While the cone is closed, the pollen grains form pollen tubes that deliver the pollen/sperm directly to the egg cells to fertilize them.
Once fertilized, a diploid zygote is formed within that female cone's ovule. This then continues to develop into an embryo inside the ovule, which is also called the seed. Once this happens, the seeds are then dispersed via:
If the seed takes, germinates and grows, it will form a sporophyte plant, and the cycle and alternation of generations will continue.
Even though gymnosperms make up only 6 percent of all vascular plants, there are still over 1,000 species of gymnosperms worldwide. These species can be categorized into four general classes, known as divisions, of living gymnosperms:
Each group has specific characteristics along with the general characteristics that all living gymnosperms share.
Coniferophyta are known by the more common name of conifers. Coniferophyta are the most common form of living gymnosperms, amounting to 588 individual species. These gymnosperms are woody plants with needle-like leaves, are almost always evergreen and have cones bearing their seeds. Almost all conifers are trees.
They're considered to be "soft wood" plants, and most are monoecious, so both male/pollen cones and female/ovulate cones are on the same tree.
Within the conifer group of plants are specific conifers that are grouped together in different genera. The largest is the genus Pinus, which consists of pines. There are 232 species within the Pinus genus including pine trees such as the red pine, bristlecone pine, white pine and so on. Other conifers include larch trees, which are in the genus Larix; spruce trees, which are in the genus Picea; and fir trees, which are in the genus Abies.
Podocarps are the next largest conifer group with 147 species of mainly tropical trees. The cypress group has 141 species that are known for their very scale-like foliage and scaly cones. The rest of the conifers are varied and different, including plants like:
While some plants in the Pinus genus are found in tropical and desert climates, the majority are found in temperate and cold and forest-heavy environments like the taiga biome and temperate forests.
Cycadophyta are also known more commonly as cycads. Unlike the Pinus plants, cycads are mostly found in tropical forests and subtropical regions.
They're almost always evergreen, of a low stature and have featherlike leaves. While many look very similar to palm trees, they aren't actually related related to palms. They are dioecious cone-bearing plants, which means they produce either male/pollen cones or female cones (not both).
While there are 10 genera and around 355 species of cycads currently known to be existing today, some of the most well known examples are:
Millions of years ago, Ginkgophyta were the dominant non-flowering plant species on Earth. However, all species except one have now gone extinct. The only surviving species in the Ginkgophyta plant division is the ginkgo biloba tree, which is also known as the maidenhair tree.
These trees are native only to China, but they have now been planted and cultivated around the world. They are some of the most durable trees currently existing. They're fire-resistant, pest-resistant and disease-resistant. It's no wonder they live for thousands of years!
Ginkgos are dioecious, meaning they produce either male/pollen cones or female cones, not both. Their leaves are distinctive bi- or multi-lobed and fan-like.
Besides ginkgos, Gnetophyta is the next smallest/least diverse of the gymnosperms. With 96 species of this kind, it can be further subdivided into three genera:
Ephedra. Ephedra are almost all shrubs or shrublike plants, and they're found in deserts or in the high mountains. These plants have small, scale-like leaves. The small size of the scale-like leaves is thought to be an adaptation to the dry environment that helps with water retention.
Unlike many of the other genera of gymnosperms, these plants can be either monoecious or dioecious. They've been used throughout history as herbal medicines and to make the drug ephedrine. Here are a few examples of common species:
Gnetum. Gnetum can be small shrubs/trees, similar to Ephedra, but they are mostly woody vinelike plants that exist by climbing on other trees/plants. They're mainly found in tropical rainforests and other tropical climates; they are native to Africa, South America and parts of Asia.
They have flat, large leaves and are monoecious (both male/pollen cones and female cones are on the same plant). Many people mistake these plants for angiosperms since they appear to have flowers. However, these "flowers" are actually just cones that appear to be flowers.
Some of the most common species are:
Welwitschia. Lastly is the genus Welwitschia. The last of the living gymnosperms in the Welwitschia genus is the species Welwitschia mirabilis.
This species is only found in the Namib Desert in Africa. Adult plants consist of two leaves that exist and grow from the beginning of their life until their end; they don't fall off, shed or replace themselves. They simply continue to grow as the plant does.
Living in the desert, it's adapted to the dry and hot environment to survive well in high heat and little water. The leaves are leathery and torn in appearance. Like ginkgoes, these plants are durable and can live to be over 1,500 years old. Similar to the related Gnetum, the Welwitschia cones appear to be flowerlike with the male/pollen cones a salmon pink color and the female cones a blue-green color.
Another unique feature for these gymnosperms is that pollination relies heavily on insects instead of depending on wind like most other types of gymnosperms. The flowerlike cones and nectar produced by the pollen cones help to attract insects for pollination. Welwitschia is the most unique of the gymnosperms because it has many varied characteristics, a one-of-a-kind growth pattern pattern, and interesting intersections and shared traits with angiosperms.
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