The flowering of aloes

This blackboard is part of the project “The Nomad Blackboard” and visually explains data about aloes.

The genus Aloe originates from southern and eastern Africa, but today it grows almost everywhere, especially in the Mediterranean and Asia. The most famous species of this genus is probably Aloe vera.

The flowers come in a wide variety of sizes, shapes, and colors. Larger species tend to have big, brightly colored flowers, while smaller species tend to display fewer flowers, but also colorful ones. Aloes start blooming at the beginning of spring when the plant is at least 3 years old. At the Marimurtra Botanical Garden, you can admire different aloe species with flowers ranging from red to orange, passing through pink and yellow. For example, you can see Aloe marlothii drawn on the blackboard with its vibrant orange and yellow flowers.

The most interesting thing about aloes is how they are pollinated. The mechanism is not the same for all species: some are pollinated by birds, others by insects, and others by a combination of both. Additionally, the species Aloe peglerae is pollinated, among others, by small mammals, such as the Namaqua rock mouse (Micaelamys namaquensis). Although some aloe species displayed at Marimurtra are pollinated by birds, this does not occur here in the Garden. Aloe marlothii, for example, originates from South Africa, where it is pollinated by different bird species, such as the white-bellied sunbird (Cinnyris talatala). Since the natural habitat of this bird is in southern and central Africa, this pollination does not take place here in Catalonia. However, unusually, some native and migratory bird species, such as the Long-tailed Tit (Aegithalos caudatus), have been observed sporadically pollinating aloes and/or other exotic plants in the Garden. This is not a natural event but rather a consequence of having plants from many different regions of the world.

The color of the flower is one of the main factors that determine which pollinators select a particular plant. While bees tend to be attracted to scented yellow and white flowers with little nectar, birds more often choose orange, yellow, or red flowers with no scent but with more nectar. Interestingly, the red coloration makes them easily perceptible and signals them as a high-energy source.

But why do some plants, like aloes, bloom at the beginning of the year, like the one you can see right now in the Garden? The key concept here is vernalization. This prevents plants from blooming in late autumn, a period often less optimal for this event. Vernalization describes the process of adequate exposure to cold (0-10°C for at least one month) followed by exposure to higher temperatures, which triggers flowering in certain plants.

Exposure to cold induces temperature adaptation responses in plants. It is believed that genetic processes are involved in vernalization. For example, in some plants, certain “flowering suppressor” proteins appear to be inhibited during the flowering process. Besides temperature, other factors such as day length and plant hormones also influence flowering.

Moreover, aloes can reproduce in two ways: sexually and asexually. The sexual reproduction method involves pollination, where pollen from the male part of a flower (stamen) is transferred to the female part (pistil). This process enables fertilization and leads to fruit formation and, ultimately, seed production. These seeds can later grow into new aloe plants, containing a mix of genetic material from both parent flowers. However, aloes also reproduce asexually through the growth of offshoots that sprout around the base of the mother plant. These shoots can be separated and replanted to grow, and they are genetically identical plants (clones). In some aloe species, up to 25 of these clones can grow in a year, making this an efficient reproduction method!

In summary, with their unique pollination process and their ability to bloom in early spring and alternatively in autumn-winter, aloes exemplify nature’s resilience and the beauty of seasonal transitions. Their flowers bring vibrant and beautiful colors to the Garden during a time when it often lacks hues.