Guest Blog Post: Researchers split the birdcatcher trees (genus Pisonia) into three

Large Cabbage trees (Pisonia grandis) dominate the landscape of a small island in the Pacific Ocean
Photo by Jean-Yves Meyer (Délégation à la Recherche de Polynésie Française, Tahiti, French Polynesia)

Guest blog post by Marcos Caraballo


The birdcatcher trees – genus Pisonia – are infamous for trapping birds with their super-sticky seed pods that would frequently entangle the body of the ‘victim’. Left flightless, the poor feathered creatures eventually die either from starvation or fatigue, or predators. Similarly notorious are the birdcatcher trees for botanists, who have been baffled by their complicated classification for the last three centuries. 

Here’s why myself and graduate student Elson Felipe Rossetto of the Universidade Estadual de Londrina (Brazil) decided to take up the untangling of this issue with our recent taxonomic studies. You can find our research paper published in the open-access scholarly journal PhytoKeys.

Ripe fruits (anthocarps) of the Birdlime tree (Ceodes umbellifera)
Photo by Ching-I Peng [deceased]

We reestablished two genera: Ceodes and Rockia, where both had been previously merged under the name of Pisonia. Now, as a result, there are three distinct lineages of birdcatcher trees from the islands of the Pacific and Indian Oceans: Ceodes, Pisonia, and Rockia.

“Previous molecular studies on Pisonia species from around the world showed that species were clustered into three major groups, and here we assign names for each of them. With this new classification, a large number of the species known as Pisonia will be henceforth named Ceodes. This includes the Parapara (Ceodes brunoniana) and the Birdlime (Ceodes umbellifera) trees, both native to many islands, including Hawaii and New Zealand. They are commonly planted in gardens for their lush and sometimes variegated foliage, as well as their fragrant white flowers. However, the Cabbage tree (Pisonia grandis) will still be technically known as Pisonia.”

adds the study’s lead author Felipe Rossetto.
Male (staminate) showy flowers of the Birdlime tree (Ceodes umbellifera)
Photo by Joel Bradshaw (Far Outliers, Honolulu, Hawaii)

Birdcatcher trees have generated much controversy in the popular media because of their seed pods (technically called “anthocarps”) secreting a sticky substance that glues them to the feathers of seabirds or other animals for dispersal. Sometimes, though, too many seed pods can harm or kill birds, especially small ones, by weighing them down and rendering them flightless. This macabre practice has led to many controversies and local campaigns aiming to remove the trees, even illegally.

Brown noddy (Anous stolidus) covered with the sticky fruits (anthocarps) of the Cabbage tree (Pisonia grandis)
Photo by Jean-Yves Meyer (Délégation à la Recherche de Polynésie Française, Tahiti, French Polynesia)

In spite of their forbidding reputation, however, we would like to stress that birdcatcher trees have positive effects on ecosystems and are important components of vegetation, especially for small islands. Sadly, there are many endemic and already endangered species of birdcatcher trees that only exist on a few small islands, where they are effectively placed at the mercy of local people.

Many species of birdcatcher trees are large and, thereby, tolerate harsh environments like seafronts and rocky cliffs, making them prime nesting spots for seabirds. Birdcatcher trees are also ecologically curious and could be regarded as keystone species in small islands, because their soft branches can sustain many types of invertebrates; their flowers are an important food source for bees and ants; their dense leaf litter nourishes the soil; and their roots have intimate interaction with native underground fungi (mycorrhiza).

All in all, clarifying the taxonomy of the birdcatcher trees is the first step to understanding how many species exist and how they relate to each other. 

Although most people relate birdcatcher trees with beaches and coastal habitats, there are species that are only found in mountains or rainforests. For example, the species now allocated to the genus Rockia is endemic to the Hawaiian archipelago. These are small trees able to grow in dry to mesic mountain forests. Using our new classification, future studies can explore in detail the hidden diversity of these enigmatic plants, and find out how trees with high dispersal capabilities evolve into species endemic to small island ecosystems.

Cabbage trees (Pisonia grandis) are important components of the vegetation in small islands due to their massive size
Photo by Jean-Yves Meyer (Délégation à la Recherche de Polynésie Française, Tahiti, French Polynesia)

About the author:

Marcos A. Caraballo-Ortiz is a research associate at the Smithsonian Institution (Washington, D.C., United States). His research interests include plant systematics and ecology, with a focus on flora of the Caribbean Islands. Dr. Caraballo-Ortiz has experience studying the taxonomy of several groups of tropical plants, with a particular interest in neotropical Mistletoes (Loranthaceae, Santalaceae, Viscaceae) and the Four O’Clock family (Nyctaginaceae). 

For more information about his projects, visit marcoscaraballo.com.

Research paper:

Rossetto EFS, Caraballo-Ortiz MA (2020) Splitting the Pisonia birdcatcher trees: re-establishment of Ceodes and Rockia (Nyctaginaceae, Pisonieae). PhytoKeys 152: 121-136. https://doi.org/10.3897/phytokeys.152.50611


New perennial brome-grass from the Iberian Peninsula named after Picos de Europa National Park

Picos de Europa National Park has given its name to a new species of perennial bromegrass, discovered in Spain. Bromus picoeuropeanus belongs to a rather underrepresented on the Iberian Peninsula perennial group within the grass genus Bromus, with the new species being just the fourth of all recognised wild species living in the Iberian territory.

Having worked on the systematics of Bromus for a long time, scientists Dr Carmen Acedo and Dr Félix Llamas, members of the Taxonomy and Biodiversity Conservation research group TaCobi of the Spanish University of León, were surprised to collect what seemed a so-far-unrecognised species of the rare for Iberia perennial group. The unlikely discovery of the new species was described and published in the open access journal PhytoKeys, while its type specimen is preserved on Herbarium LEB.


This is the preferred habitat of Bromus picoeuropeanus in stony and unstable soils, c. 1900 m elevation.

Failing to understand how it was possible that the new species has never been found in the over-studied territory of Picos de Europa National Park, the two researchers traveled back to the classic locality to confirm its presence and study the habitat. Interestingly, while the new species is located in a typical for the National Park habitat, only a single perennial Bromus species was previously known from the area.

Eventually, having spent more time studying and collecting samples of different taxa in the Park, the authors discovered several more individuals of the new species dwelling in stony areas at an altitude of 1600 – 2200m. While herbarium collections from the National Park revealed that samples were also collected some years ago by another botanist, the scarcity of populations of the new species is still striking given the abundance of other brome-grass species.

Unlike its sister species, the Picoeuropean brome-grass is a small rhizomatous herb up to 70 cm high. Another easy-to-recognize difference is its well-developed subterraneous vegetative organ, forming a long rootstalk called rhizome, which is an easy distinctive trait.

“Given the inaccessibility of the areas, the mountainous topography and the few grass-species-loving botanists, this species was ignored until now. Probably the genus Bromus has undergone some local speciation on this isolated place, but exactly how this occurred requires further investigation,” explain the authors noting the isolation of the new species from its relatives in the area.

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Original Source:

Acedo C, Llamas F (2019) A new species of perennial Bromus (Bromeae, Poaceae) from the Iberian Peninsula. PhytoKeys 121: 1-12. https://doi.org/10.3897/phytokeys.121.32588

Invasive alien plant control assessed for the Kruger National Park in South Africa

Along with urban and agricultural encroachment and pollution mitigation, managing invasive alien species is a key intervention needed to protect biodiversity. Unfortunately, on a global scale there are not enough funds to meet the requirements for effective conservation everywhere, which means that scarce funds need to be allocated where they can be used most efficiently.

In order to find out whether the historical measures undertaken at the Kruger National Park in South Africa have been effective and optimised, researchers led by Prof. Brian W. van Wilgen of Stellenbosch University assessed the invasive alien plant control operations in the protected area over several decades. Their findings and recommendations are published in the open access journal Neobiota.

While the first invasive alien plants in the national park, which stretches over two million hectares, were recorded back in 1937, it was not until the mid-1950s that attempts at controlling them began. By the end of the century, the invasive alien plant control program had expanded substantially.

Dense invasions of the West Indian Lantana (Lantana camara) along the Sabie River in the Kruger National Park have required intensive mechanical and chemical control to clear.
Dense invasions of the West Indian Lantana along the Sabie River in the Kruger National Park have required intensive mechanical and chemical control to clear.

However, the scientists found out that despite several invasive alien species having been effectively managed, the overall control effort was characterised by several shortcomings, including inadequate goal-setting and planning, the lack of a sound basis on which to apportion funds, and the absence of any monitoring of control effectiveness.

Furthermore, the researchers report that over one third (40%) of the funding has been spent on species of lower concern. Some of these funds have been allocated so that additional employment could be created onsite, or because of a lack of clear evidence about the impact of certain species.

As a result of their observations, the team concludes three major strategies when navigating invasive alien species control operations.

Firstly, a thorough assessment of the impact of individual species needs to be carried out prior to allocating substantial funds. On the other hand, in case of a new invasion, management needs to be undertaken immediately before any further spread of the population and the subsequent rise in control costs. Monitoring and assessments have to be performed regularly in order to identify any new threats that could potentially be in need of prioritisation over others.

Secondly, the scientists suggest that the criteria used to assign priorities to invasive alien species should be formally documented, so that management can focus on defensible priorities. They propose using a framework employing mechanisms of assessments used in the International Union for Conservation of Nature‘s Global Invasive Species Database.

The authors also point out that re-allocating current funds to species of greater concern is needed for species that cannot be managed via less expensive solutions such as biological control. Taking care of alien plant populations living outside of the park, but in close proximity, is also crucial for the prevention of re-invasions of already cleared areas.

Sunset Dam heavily infested with water lettuce (left). The population was effectively eliminated by a combination of biological and chemical control (right).
Sunset Dam heavily infested with water lettuce (left). The population was effectively eliminated by a combination of
biological and chemical control (right).

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Original source:

van Wilgen BW, Fill JM, Govender N, Foxcroft LC (2017) An assessment of the evolution, costs and effectiveness of alien plant control operations in Kruger National Park, South Africa. NeoBiota 35: 35-59. https://doi.org/10.3897/neobiota.35.12391