The fantastic world of plant sexuality

Like humans, plants are born, grow, reproduce, and die. In an asexual or sexual way, naturally, with technical intervention or with the intervention from pollinating animals, Nature multiplies and plant sexuality is one of the essential tools for this to happen. Find out in in this article what lies behind the “magic” of plant reproduction.

In an ever moving world, we don’t always question the simplest things. Have you ever inquired about plants’ sexuality? How do trees reproduce even without human intervention?

Who has never spent long minutes admiring a garden, watching the details: a bee pollinating a flower; a bird dropping a seed it carried in its beak for kilometres; or a gardener breaking the silence and pruning a tree? Even the seemingly most banal events, like a “butterfly effect”, play a role in the emergence of a new plant.

The sexuality of plants is far from linear, and can happen in a sexual way (the union of female and male gametes) or in an asexual way (vegetative propagation, the new plant is genetically equal to the initial organism). Nevertheless, there are “actors” in a supporting role this story that can play a fundamental role in it: pollinating agents – bees, other animals and even the wind –, and people planting new areas or reformulating existing ones.

Plant sexuality: asexual reproduction

We have a lot in common with plants but there is also a lot that separates us. With regard to plant sexuality, one of the biggest differences is that some species reproduce asexually. Known as vegetative or clonal propagation, asexual reproduction happens when one plant can generate another without the junction of female and male gametes.

Without the intervention of pollinators and human techniques, plants reproduce naturally, resulting in their “clones”; that is, plants exactly the same as the original, both genetically and morphologically. However, this may represent a disadvantage in evolutionary terms, as the existence of unfavourable characteristics in certain environments may affect the capacity of a species to grow.

The discovery of this possibility was truly revolutionary for the knowledge about plants and humans benefit from this ability to propagate plants with certain characteristics, namely to produce more resistant plants. This methodology allows greater control over the production of orchards, for example, betting on more productive trees which are more likely to resist pests and other types of diseases and better suited to a certain soil or climate – this resilience is, in fact, the main characteristic in the selection of individuals to propagate, both in agriculture and in the woods.

Asexual reproduction can happen naturally, for example, by:

• Apomixis: somewhat similar to sexual reproduction, since it also involves an embryo, although it is formed without gamete fusion. In these plants, there is no pollen fertilization and the split of a diploid cell (cell nucleus with two series of chromosomes) originates embryonic development.
  Some examples of plants that reproduce by apomixis: dandelions, blackberries and some grasses, such as the smooth-stemmed dog hair (Poa pratensis), in the image.
• Sprouting: The mother plant creates sprouts in itself. They can germinate in colonies – if they grow attached to the organism – or, at some point in the reproduction process, separate and result in a new plant.
  Some examples of plants that reproduce by budding: cherry trees and citrus trees, peach trees, apple trees, in the image, and walnut trees.
• Fragmentation: in trees, when the branches have buds (plant formation, ovoid or subglobose), these can detach, for example, due to the wind or the action of some animal, leading to their fragmentation. If, when they reach the soil, favourable conditions exist, they can result in a new plant.
  Some examples of plants that reproduce by fragmentation: the willow and the Kalanchoe daigremontiana, in the image

Plant sexuality: asexual reproduction

We have a lot in common with plants but there is also a lot that separates us. With regard to plant sexuality, one of the biggest differences is that some species reproduce asexually. Known as vegetative or clonal propagation, asexual reproduction happens when one plant can generate another without the junction of female and male gametes.

Without the intervention of pollinators and human techniques, plants reproduce naturally, resulting in their “clones”; that is, plants exactly the same as the original, both genetically and morphologically. However, this may represent a disadvantage in evolutionary terms, as the existence of unfavourable characteristics in certain environments may affect the capacity of a species to grow.

The discovery of this possibility was truly revolutionary for the knowledge about plants and humans benefit from this ability to propagate plants with certain characteristics, namely to produce more resistant plants. This methodology allows greater control over the production of orchards, for example, betting on more productive trees which are more likely to resist pests and other types of diseases and better suited to a certain soil or climate – this resilience is, in fact, the main characteristic in the selection of individuals to propagate, both in agriculture and in the woods.

In trees such as the laurel tree, flowers may be present on different plants (dioecious species), while in monoecious species such as the holm oak tree, flowers of different sexes may be found on the same tree. The fertilization process begins with pollination: the pollen generated in the male organ, more specifically in the anthers, reaches the gynoecium (female organ) and this fertilization results in the seeds from which other plants will be born.

Seed-producing plants can be of two types:

• Angiosperm group: the flowers that are at the origin of the reproductive process are considered true flowers and have petals. The eggs and future seeds are found inside closed ovaries that will give rise to the fruits, and this is the most common type of plant present worldwide. Examples: pear, apple, eucalyptus and oak.
• Groups of gymnosperms: they do not have true flowers, nor petals and, consequently, do not have closed ovaries, nor do they produce fruit. In any case, plants have sexual structures: pollen is produced and the process then takes place in the female structures, producing the seed. Examples: pine tree, cypress, sequoia and fir.

With regard to plant sexuality, this type of reproduction offers greater genetic diversity, unlike asexual plants, which are genetically the same as the parent plant. The junction of the gametes provides new characteristics and greater adaptability. This strategy is also explored by human action, with the installation of beehives, for example, to enhance pollination in forests and orchards.

Nature multiplies and renews itself and is constantly changing, evolving and adapting to the demanding needs that have been presented over time. Only the fittest can survive and endure in time, and this knowledge they “carry” in their roots helps human beings – and production using technology – when it comes to adapting plants to edaphoclimatic conditions (that is, soil and climate conditions) an to allow them to resist, increasingly, new pests and diseases. The selection of species through the environment and control over their reproduction is fundamental for good resource management and even for the survival of some species, which can thus respond to the exiting conditions in a given area.

This is a story that is written naturally, an evolution of millions of years that continues to be written every day, in the green landscapes that surround us, and which Man draws inspiration from.