Rising from the ashes: The “Phoenix plants” that flower the next day after burning

Imagine that you are going on a hike for two days through the savannas of the Cerrado in Central Brazil. On the first day, you see a fire consuming all the plants in the landscape, with flames several meters high. You are not that shocked since you were already told that wildfires are part of the natural dynamics of this ecosystem. The next day, you make your way back and went through the same path as before. Naturally, you expect to find a desolate landscape completely covered in ashes, but instead, you see several plants starting to flower! This may sound like the Greek and Egyptian myth of the Phoenix bird that is reborn from its ashes, but in this case, it’s a plant, and it’s in Brazil, and it’s true!

Such an unexpected encounter with speedy-blooming species occurred with Dr. Natashi A. L. Pilon (@natashipilon on Twitter) and her research team. She gave an interview for Botany One and told us that as a biologist, she always liked to go to recently burned areas to see how plants and animals responded to fire events. However, this time she went to the field the next day after a controlled fire, a common practice in fire-prone ecosystems like the Cerrado. To her surprise, she found not one but two sedge species starting to release inflorescences in less than 24 hours: Rhynchospora confusa and Rhynchospora terminalis (both from the Cyperaceae family). Interestingly, such rapid blooming was already known for Bulbostylis paradoxa, another Cerrado species from the same family. This finding is of great importance because it suggests that such speedy blooming is not uncommon in this ecosystem.

Pilon has been working in the Cerrado region for several years and had never been able to identify the species that were always in the vegetative form until fire revealed the flowers! Finding individuals of these species flowering without the stimulus of fire is rare. In fact, although they can be found in a large part of the Cerrado, there are few herbarium samples with flowers and most of these have fire scars, implying that finding these species flowering is more likely after a fire. This suggests that individuals can go without blooming for several years, just waiting for their moment to burn! But after all, what is the advantage of flowering so quickly? Pilon and her collaborators suggest that the benefits might be related to a better exploration of the resources associated with post-fire conditions. For instance, being the first flowers to appear in burned areas allows these plants to monopolize pollinators. Likewise, the seeds produced and dispersed will have more space, light, and nutrients to grow.

Fire does not kill these plants because they have specific resistance mechanisms. Rhynchospora confusa and Bulbostylis paradoxa have a well-developed aboveground caudex, a type of stem whose leaf sheaths remain and protect the buds. On the other hand, Rhynchospora terminalis have a resistant belowground rhizome protected by dead sheaths. What remains a mystery is the physiological mechanism that triggers such fast responses. Are the flower buds already there and only grow after a fire, or do plants produce them from scratch? Which hormones are involved in the process?

We are already in the 2020s, and a question remains: why has nobody noticed this during the several previous decades of research? Pilon advocates that the herbaceous flora and the Cerrado open formations are still neglected and most of the research has been conducted with woody species. However, open formations have a fundamental role in the ecosystem functioning, bearing a unique biodiversity that is important for the conservation of the Cerrado biome as a whole, and with many fascinating stories that are new to science. According to Pilon, it is likely that there are other species with such behavior in the Cerrado. When asked if this one-day speedy blooming occurs in other plants of the world, Pilon said that although it has not been reported yet, it is possible that this phenomenon also occurs in different fire-prone ecosystems since many plants have similar morphologies to the Brazilian ones, especially some Cyperaceae.

Post-fire massive flowering is not uncommon in fire-prone ecosystems and has been reported for hundreds of Cerrado species. So, what is so unique in these “Phoenix plants” that quickly bloom after less than 24 hours? Besides being just amazing, they open new avenues of research and show an extreme case of adaptation. Due to fragmentation and habitat loss in the Cerrado, natural fires caused by lightning have become uncommon. Therefore, these plants may suffer local extinction without fire due to demographic problems and the increased density of woody plants. This is why Pilon suggests that controlled fire is important for maintaining biodiversity. Since fire has been present in the Cerrado for thousands of years, this has led species to adapt their life histories to this recurrent and natural phenomenon. As Pilon wisely says: “Fire is not a disturbance, but a natural part of the system”. The research results of Pilon and her team show how a botanist’s curiosity can yield fascinating stories about how ecosystems function and how this knowledge can help us to conserve them.

READ THE ARTICLE:

Pilon, N. A., Freire, C. T., Oliveira‐Alves, M. J., & Oliveira, R. S. (2023). Speedy blooming in Cerrado after fire is not uncommon: New records of Cyperaceae species flowering 24 h after burning. Austral Ecology. https://doi.org/10.1111/aec.13326

João C. F. Cardoso is a Brazilian ecologist. His research focuses on the interactions between plants and animals and between plants and the environment, especially in the Brazilian Cerrado savanna. Specialized in pollination, he is passionate about the history and natural history of plants and loves rare and specialized interactions.