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Jose Gamarra

Jose Gamarra standing

Galapagos Tortoise Expert

The Successful Child of the Galapagos

The Scalesia is the counterpart of Darwin’s finches in the plant world. Just like the Darwin’s finches, it is composed of 15 different species that are spread all throughout the Galapagos Archipelago. The Scalesia is one of the seven endemic plants genera to the Galapagos islands. It is found in the five biggest islands: San Cristobal, Santa Cruz, Santiago Isabela, Fernandina, and Floreana.

Photo of Scalesia.  Galapagos Islands.

The Scalesia shares the same “blood” as the daisies. It is part of the Asteraceae family, just like the daisies, lettuces, marigolds, and chamomiles. Indeed, the Scalesia shares a unique blood line since the name Asteraceae comes from the type genus Aster, meaning star, which refers to the star-like form of the flower. Moreover, the Asteraceae family can be found in North America, South America, Europe, Asia, Australia, Oceania, and the Galapagos. The Galapagos was recently colonized around two million years ago by the fearsome Scalesia warrior.

The lineage of the Scalesia is a toddler in the eyes of evolution. Schilling et al. suggest that Scalesia diverged from the sister taxon Pappobolus (a mainland brush) approximately 1.9- 6.2 million years ago[1]. The lineage was recently born or, to be more accurate, diverged from its mother, Heliantheae. Moreover, the time of “birth” of the Scalesia ruled out the fact that it might have divided in the mainland since the Galapagos formed 5-10 millions of years ago, and there is no species of Scalesia in the mainland. However, this is not certain because Scalesia could have disappeared from South America a long time ago, and migrated to the Galapagos. Knowing the time of the Scalesia diversification by using its “family tree” is intriguing to the science world since it put us one step forward in determining its “true place of origin.” Getting close to the answer is important for it can be lead to new methods of research never used before. This would be a breakthrough in science since these new methods can be applied to other species in the Galapagos.

Understanding a family tree is just like understanding the relationship of the Scalesia and the Asteraceae family. A family tree can trace events back in time so the new generations can reflect from their ancestors.  In the case of the Scalesia, its “family tree” traces changes in time such as genetic relation, and physical and genetic adaptations that made the Scalesia adapt to the Galapagos successfully. Just like one would use a normal family tree to trace back the history of one’s family, one can utilize the Asteracea family tree to trace back the genetic evolution of the Scalesia in the Galapagos by using the DNA of the Scalesia to compare it with other species in the Asteracea family.

The Scalesia is like a spoiled princess that can do anything it pleases to get what it wants. The Scalesia wants to succeed in various habitats so it is capable of growing as either a shrub or a tree to match the conditions of each ecosystem. Thus, there are only three tree-like species of Scalesia—S. pedunculata, S. cordata, and S. microcephala. The rest only grow as shrubs in the Galapagos. Each of the species adapted to different ecosystems across different islands; just like invasive species, they can survive in different habitats. As a result, they can interact differently in each ecosystem, or occupy different niches. All these circumstances are part of a process known as adaptive radiation since every edge of the Galapagos screams out evolution in process.

Every species of Scalesia has a similar stem structure, and acquire unique kinds of flowers and leaves. They have soft bark and a sponge-like structured stem that transports water and nutrients to every part of the organism. With daisy-like flowers, the Scalesia is often referred to as the “daisy tree” in Spanish. However, the most noticeable aspect of the Scalesia is its different types of leaves. Just like the finches’ beak size, the leaves come in different shapes, sizes, and forms that are unique to each individual species and environment.

The most famous and widespread species is Scalesia pedunculata, which can be found in humid and windy areas of Santa Cruz, San Cristobal, Santiago, and Floreana. Scalesia pedunculata is one of the largest growing Scalesia species. This species can grow to a height of 15 to 20 meters tall in just a few years.  It is difficult to miss this species because it covers most of the highland regions in the Galapagos. They are the most talked-about plant species by tour guides.

The Scalesia has a strange lifestyle. Most of the species are found within arid habitat and transition areas that link two different habitats together. S. pedunculata, S. cordata, and S. microcephala occur in dense forests as the dominant plant species. These species usually grow in groups of individual that are the same height and age. They all reach maturity after 15 years. El Nino, droughts, and floods can cause entire forests of Scalesia to collapse. However, they reproduce at the same rate, allowing the new generation of seedlings to regrow. In other words, they live together and die together. They are worse than the three musketeers.

Various species of Scalesia can control their reproduction based biotic and abiotic conditions from the environment. They have various reproductive characteristics that enhance their survival on a certain island. Nielson et al. suggest that in the case of S. affinis, if needed, sexual reproduction was favored more than asexual reproduction[2]. In favored conditions, such as persisting rainfall and proximity of individuals to each other, S. affinis prefers to reproduce sexually.  Genetic variation in a population is necessary to ensure that the species is capable to survive drastic changes in its environment. However, in unfavored conditions, such as droughts or the introduction of a plant to its environment, the species prefers to reproduce asexually since it ensures the spreading of the species by increasing the population size of the fittest individuals. The Scalesia can be a dad and a mom at the same time—just when the Scalesia needs it.

The Scalesia is a capable plant that can survive by itself. Nielson et al. suggest that Scalesia is a great example of Baker’s law—a theory about self-compatible plants having a selective advantage in island colonization as they do not require the introduction of other plants to survive [2],[3]. The Scalesia is found in different habitats by using similar or different mechanisms of survival within themselves. For example, plants reject pollen particles that come from the same plant when conditions are favored. 

Different species of Scalesia are successful in their own environment only. Schmidt and Skowe suggest that different species of Scalesia interact with certain soil fungi that produce nitrogen [4]. Every species has a different type of roots because certain species of Scalesia can grow optimally or not grow at all in certain clades of fungi. Different forms of roots are capable of maximizing the absorption of nitrogen from a certain soil fungi. Therefore, two or more species of Scalesia cannot compete in the same environment because each environment favors one or more species over the others. An environment favors a relationship where organisms are capable to thrive together. This is a great evidence of adaptive radiation because the Scalesia was able to occupy certain environments by interacting with organisms differently, and adapting to those interactions. It needed to change certain aspects of its physical shape in order to be successful in such an environment.

The Scalesia is a great example of evolution in the plant world. It was capable of diverging and adapting to the Galapagos in a short time, compared to the origin of the Galapagos archipelago, successfully. It is found in different habitats throughout the whole archipelago since every species adapted different physical characteristics based on the conditions given by a certain ecosystem. The conservation of Scalesia depends on the conservation of terrestrial organism since the Scalesia’s survival is mostly based on symbiotic relationships with soil fungi. Thus, the conservation of the Galapagos’ terrestrial ecosystems is pivotal since it is beneficial to the Scalesia and the role it plays in its various habitats. Each species of Scalesia is attached to the life on its island, which makes them more vulnerable to drastic changes. Therefore, it is important to conserve the Scalesia because it brings soil composition stability, and is vital for the survival of other organisms. 

[1] Edward E. Schilling, Jose L. Panero, Uno H. Eliasson (1994). Evidence from Chloroplast DNA Restriction Site Analysis on the Relationships of Scalesia. American Journal of Botany, 81. 2, 248- 254.

[2] Lene Rostgaard Nielson, Hans R. Siegismund, Marriane Phillip (2003). Partial self- incompatiblity in the polyploid endemic species  Scalesia Affinis  (Asterecae) in the Galapagos: remnants of a self incompatility system? Botanical Journal of the Linnean Society, 93- 101.

[3] Herbert G. Baker (1967). Support for Baker's Law-As a Rule. Evolution 21.4, 853- 856.

[4] Steve K. Schmidt, Kate M. Skowe (1986). Michorrizal Fungi on the Galapagos Islands. Biotropica 18.3, 236- 240.