Today on HerbSpeak, we are going to discuss the birds and the bees, as well as a whole bunch of other fascinating methods of plant reproduction.
There are such an interesting variety of plants out there, and each one has their own unique way of reproducing with themselves or other plants around them.
Some can produce offspring without any help from another organism, dividing asexually, while others reproduce with the help of a pollinator, bringing pollen to a female ovary of another fruit – and yet others take a page out of the mushroom’s book and produce spores.
What is Plant Reproduction?
Because plants are a living organism, their goal is ultimately survival and reproduction, as with any other living organism. The goal of this reproduction process is to create a new generation of functional plants to carry on the genetic codes and continue to thrive with improved environmental response and function.
Plants may reproduce through sexual or asexual methods, and it can seem like each method is unique to each plant.
Fortunately, there is plenty of research that has been done on plant reproduction that helps us understand each process, as there is no one-size-fits-all method for the plant kingdom.
One common misconception is that for a plant to sexually reproduce, it must have a bright, large flower. While flowering plants (angiosperms) make up the bulk of the known plants on the planet, they may either reproduce sexually or asexually.
Angiosperms make up an estimated 300,000 of all plant life on the planet, out of an estimated 391,000 plants as of 2016, with thousands more discovered each year. (1)
We have counted the currently known, described and accepted number of plant species as ca 374,000, of which approximately 308,312 are vascular plants, with 295,383 flowering plants.
Contrary to popular belief, these flowering plants do not necessarily have bright, overt petals to display like we would normally think of flowers as having; grasses, for example may have the constituent parts necessary for them to be considered angiosperms without the showy petals, making it difficult to identify as a common “flowering” plant.
Gymnosperms are the second most common class of plant known in the world today, and they differ in that they do not protect their seeds within an ovary or fruit.
These plants still produce ovules within their cones, rather than inside an ovary, which can be pollinated to produce what is called a naked seed due to its lack of protection. The four main groups of gymnosperms include conifers, cycads, gnetophytes, and ginkgo.
This type of plant relies on other methods of reproduction, such as spore dispersal, rhizome propagation, or fragmentation.
Why is Understanding Plant Reproduction Important?
Understanding plant reproduction is critical in understanding how plants function from both an agricultural and ecological standpoint.
Not only does it help us better understand the world around us, but it can alert us to how we are affecting the environment, or to other problems in the environment that might be affecting the typical plant reproduction process.
How Do Plants Reproduce Sexually?
Sexual reproduction requires genetic material from two parent plants. These parent plants must have sex cells, called gametes, which represent the female and male parts.
When the female and male gamete mix, the plant becomes fertilized and produces offspring: the seed.
This is the most widely known method of pollination, and likely what you think of when you imagine the birds and the bees talk in any literal sense. This is the method of pollination where the pollen is transferred between the anther and stigma of different flowers.
The cross-pollination process may take place on different flowers on the same plant, or on a different plant entirely.
This is a less widely known method of pollination, but it is quite common. This happens when the pollen transfer occurs between the anther and stigma of the same flower on the same plant. This self-pollination might be considered asexual in other species, but it is common in both plants and insects.
This self-pollination process may take plant on the same flower of the same plant only.
How Do Plants Reproduce Asexually?
There are many plants which reproduce asexually, meaning no flowers are required for fertilization. These plants are often capable of self-reproduction. Fortunately, because asexual reproduction does not require another plant, this speeds up the process and allows the plant to propagate itself widely.
When a plant buds, it grows a small bud through targeted cell division. These are commonly referred to as the buds or “eyes” and may grow into plants which are clones of the original plant.
For example, ginger, onion, dahlias, potatoes, and many other plants grow from the buds that form on the surface of the plant. These eyes can sprout under favorable conditions, producing leafy shoots and growing into a new plant.
Vegetative reproduction is an asexual method of reproduction performed a multitude of ways depending on the plant. For example, fragmentation is a form of vegetative reproduction that occurs when a frond, leaf, or root touches the ground and begins growing a new plant from the contact with the soil, or when roots extend and begin creating new plants underground.
Another example of fragmentation performed by liverworts and mosses are tissue buds called Gemma which disperse through rainwater and form new plants wherever they land.
There is a litany of terminology in vegetative reproduction that depends highly on the anatomy of the specific plant discussed.
Sporogenesis Highlight: Plants That Produce Spores
Sporogenesis is perhaps one of the most fascinating methods of plant reproduction. There are many plants that we all know and love which utilize spore dispersal as their only or primary form of propagation, much like fungi, which belong to their own kingdom of life on the planet, separate from plants and animals.
Spore plants are considered one of the oldest types of plants in history and belong to a class of plants called bryophytes and pteridophytes.
The spores produced on the underside of these plants’ fronds allow the plant to reproduce, spreading the species far and wide through wind or animal dispersal. After the spores have landed is when the fertilization process begins, rather than before dispersal like in angiosperms.
Now, spore-producing plants are not necessarily different from asexual or sexual plants. They still must interact either sexually or asexually to produce a new plant. (2) They simply have a unique way of handling the process.
Both male sporocytes (microsporocytes) and female sporocytes (megasporocytes) will then undergo meiosis to give rise to the microspores and megaspores, in the male and female organs, respectively.
Liverworts, hornworts, and mosses are all considered bryophytes, which are nonvascular plants. Clubmosses, spikemosses, horsetails, quillworts, and ferns, on the other hand, are considered pteridophytes, which are vascular plants. These plants reproduce both sexually and vegetatively.
In fact, if you have ever owned a fern or observed one in the right season in nature, then you know that these plants reproduce via spores on the underside of their fronds. These spores release and catch on the wind, dispersing to other areas.
In bryophytes, sexual reproduction requires the male and female plant to interact without the use of pollen. Luckily, this plant has motile sperm and lives in environments that are moist most of the time. Bryophyte sperm must swim from the antheridium – the male sex organ – to the archegonia – the female sex organ – through the moist environment these plants live in.
Algae is a separate class of organisms, which also reproduce via spores or cell division. Larger species of algae can reproduce with spores, while smaller species tend to reproduce by cell division or fragmentation. Algae may reproduce either sexually or asexually depending on the species. Most methods of algae reproduction rely on spores – which can either be motile or nonmotile – traveling on water currents to reach a compatible match.
- Maarten J.M Christenhusz, The Number of Known Plant Species in the World and Its Annual Increase, https://www.biotaxa.org/Phytotaxa/article/view/phytotaxa.261.3.1
- Li Yuan, Spore Formation in Plants: Sporocyteless and More, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4650592/