Plants have the amazing ability to multiply themself into hundreds and thousands once the condition is favored. In the process of spreading the progeny from the parent plant, every plant cell literally has the potential to develop into a new plant. As rooted and sessile organisms, in order to expand their territories and occupy more land, plants must catch every opportunity that spreads their offsprings. Anything that moves around them could serve as transportation vehicles, the wind, the flowing water, the insects, other animals, and humans. As a result, extensively creative and diversified strategies for reproduction are observed in the plant world, in which they dressed up as the best passengers that suitable for boarding onto the vehicles. And thanks to their abundance and supreme ability to multiply, in which other lives including humans are supported and thrived.
There are mainly two types of reproduction, the first is the more genetically conservative through the asexual method, and the other is the sexual reproduction which introduces variation through genetic recombination. In asexual reproduction, the new plant arises from a segment of the mother plant or a specialized reproductive structure without the fusion of gametes. Whereas sexual production occurs when there is the fusion of gametes, male gamete from pollen, and the female gamete from the ovules, also known as fertilization from the sexual reproductive organs of the same or different plants. Sexual reproduction is also characterized by meiosis that the embryo received half of its genetic contents or information from each parent. It’s important for plants to have the ability to reproduce in two different ways. Not just to add up the copies of themselves as the base but also to gain genetic diversity and resilience into the ever-changing environments. Asexual reproduction is more self-sufficient, whereas sexual reproduction is strongly dependant on environmental factors such as temperature, salinity, nutrients, day length (total light received per day), and the presence of pollinators.
There are several reproductive stages. First, gametophyte, a haploid (half set of genetic contents) of the life cycle of plants which denoted as “n”, during which gametes are produced through mitosis. It arises from a haploid spore produced by meiosis from a diploid sporophyte. Second, sporophyte, the spore-reproducing diploid generation, which denoted as “2n” in the life cycle of plants. Third, alternation of generation. It is an alternate development of two types of individuals in the life cycle of an organism. Usually, one type reproduces asexually, and the other type reproduces sexually. The third term is restricted to the organisms with a haploid generation (n), alternating with diploid generation (2n). For instance, a haploid phase, during which gametes (n) are produced by mitosis (gametophyte phase), alternates with a spore-producing diploid (2n) (sporophyte) phase.
The most common method of reproduction in algae, which is the primitive plants, is by binary fission, or multiple fissions through any vegetative part of the thallus to develop into new individuals that are identical to the parent cell. It does not involve any spore formation and there is no alternation of generations. It’s also known as vegetative reproduction via mitosis or by segmentation. Some large algae developed the ability to reproduce by spores that germinate into a new organism in the presence of water as the media. This is asexual reproduction which involves the formation of certain types of spores but without any sexual fusion. Each spore germinates into a new plant. In this method, there is no alternation of generations. Monospores characterized as walled, non-flagellate, and spherical cells are observed on some red algae; aplanospores that are non-motile spores are found from some green algae; zoospores that lack true cell walls and having one or more flagella is also one of the asexual propagation of algae. The advantage of having flagella is to allow the zoospores to swim to a favorable environment, whereas both monospores and aplanospores are relying on the water as the transporting media.
For lower plants such as mosses, liverworts, and hornworts, the gametophyte is the dominant and conspicuous generation. The reproductive mechanism of moss is similar to that of fern. The only difference is that there are male and female gametophytes (n) in the moss reproductive cycle and the fusion of the gametes is required to produce sporophytes (2n). Moss is highly regenerative in which it can be regenerated through the splitting of the crown or some mosses can be propagated by grinding the moss onto a substrate.