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


Major advances in our understanding of New World Morning Glories

John Wood of the Oxford team members collecting plants in Bolivia
Photo by BRM Williams

A major advance in revealing the unknown plant diversity on planet Earth is made with a new monograph, published in the open-access, peer-reviewed journal PhytoKeys. The global-wide study, conducted by researchers at the University of Oxford, lists details about each of the 425 New World species in the largest genus within the family of morning glories, thanks to an all-round approach combining standard, modern and new-generation identification techniques. 

The family of morning glories, also known as bindweeds, whose scientific name is Convolvulaceae, includes prominent members like the sweet potato and ornamental plants such as the moonflower and the blue dawn flower. In fact, one of the key conclusions, made in the present work, is that within this plant group there are many other species, besides the sweet potato, that evolved storage roots long before modern humans appeared on Earth. Furthermore, most of those are yet to be evaluated for economic purposes.

Sweet potato (Ipomoea batatas) growing as a weed in a waste ground, San Ramon, Peru
Photo by Robert Scotland

To make their findings, the research team of John Wood, Dr Pablo Muñoz Rodríguez, Bethany R.M. Williams and Prof Robert Scotland applied the “foundation monograph” concept that they had developed for similarly diverse and globally distributed, yet largely understudied groups. Usually, such groups with hundreds of species have never been surveyed across their entire geographical range, which in turn results in the existence of many overlooked new species or species wrongly named.

As a result, the monograph adds six new to science species and establishes nine new subspecies, previously recognised as either distinct species or varieties. The publication also cites all countries where any of those 425 morning glories occurs. In order to provide detailed knowledge about their identities and ecologies, the authors also produced over 200 illustrative figures: both line drawings and photos.

In their study, the scientists also investigate poorly known phenomena concerning the genus. For instance, the majority of the plants appear to originate from two very large centres, from where they must have consequently radiated: the Parana region of South America and the Caribbean Islands. Today, however, a considerable amount of those species can be found all around the globe. Interestingly, the team also notes a strong trend for individual species or clades (separate species with a common ancestor) to inhabit disjunct localities at comparable latitudes on either side of the tropics in North America and South America, but not the Equator.

Prof Robert Scotland (University of Oxford) with the evolutionary tree of Ipomoea that includes 2000 specimens sequenced for DNA
Photo by John Baker

The monograph exemplifies the immense value of natural history collections. Even though the researchers have conducted fieldwork, most of their research is based on herbarium specimens. They have even managed to apply DNA sequencing to specimens over 100 years old. The publication also provides detailed information about the characteristics, distribution and ecology of all the species. It is illustrated with over 200 figures, both line drawings and photos.

“A major challenge in monographing these groups is the size of the task given the number of species, their global distribution and extensive synonymy, the large and increasing number of specimens, the numerous and dispersed herbaria where specimens are housed and an extensive, scattered and often obscure literature,”

comment the scientists.

“Unlike traditional taxonomic approaches, the ‘foundation monograph’ relies on a combination of standard techniques with the use of online digital images and molecular sequence data. Thereby, the scientists are able to focus on species-level taxonomic problems across the entire distribution range of individual species,”

they explained.

***

In a separate paper, published in Nature Plants last November, the research team provides further insights into how they have assembled the monograph and include all the molecular sequence data and phylogenetics produced during their work.

***

Original source:
Wood JR.I, Muñoz-Rodríguez P, Williams BR.M, Scotland RW (2020) A foundation monograph of Ipomoea (Convolvulaceae) in the New World. PhytoKeys 143: 1-823. https://doi.org/10.3897/phytokeys.143.32821