Ricardo Bressan Pacifico
Plant systematics and biogeography lab - Maringá State University, Maringá, Brazil
With Halloween just around the corner, our taxon of the month is a recently described and unique genus of plants with unusual feeding habits, Philcoxia. This genus was first described 17 years ago, known only from three species (Taylor & Souza, 2000), although since then several additional species were recently discovered bringing the number of species in the genus to seven (Scatigna et al., 2015; 2017). All Philcoxia species are rare and are endemic to central Brazilian mountaintop grasslands, usually known as campo rupestre (Taylor & Souza, 2000). They are annual herbs, usually less than 30 cm tall, with delicate roots and stems, and small white to purple flowers measuring less than 1 cm in length. However, the most striking features of Philcoxia took more than a decade to be discovered. All species have underground leaves to which many nematodes attach and these leaves look somewhat similar to those found in carnivorous plants, a feature which caught the attention of researchers from California and Brazil, who decided to perform carnivory tests (Fritsch et al., 2007). The initial carnivory test results were negative (Fritsch et al., 2007), however, a few years later, a new and creative experiment shed light on this matter. In this experiment, radioactive nitrogen (15N) was used to feed bacteria (Escherichia coli) that were fed to to a population of nematodes (Caenorhabdtis elegans), which, in turn, were placed over the underground leaves of Philcoxia minensis for two days. The idea was to track the nutrient acquisition of Philcoxia, i. e., to see if the radioative nitrogen from nematodes would somehow be absorbed by this plant. The fast absorption of the 15N revealed by the elevated concentration of it in Philcoxia leaves strongly suggested that the nematodes were digested (instead of naturally decomposed) and absorbed by Philcoxia leaves (Pereira et al. 2012) suggesting that this genus of plants is carnivorous and feeds on nematodes. Carnivory evolved at least six times within angiosperms (flowering plants) and about 20 carnivorous genera distributed in 10 distinct families have been identified. A general cost–beneﬁt model predicts that carnivory will be restricted to well lit, low-nutrient areas, where the major source of important nutrients such as nitrogen and phosphorus will be obtained from captured and digested invertebrates (Pereira et al. 2012). Philcoxia, like other carnivorous plants, live in nutrient-poor soils and are the only known carnivorous plants in the Plantaginaceae family (Pereira et al. 2012). The unusual new mechanism of carnivory discovered in Philcoxia caught public attention in high impact scientific journals such as Nature (Rowland, 2012).
Fritsch, P. W., F. Almeda, A. B. Martins, B. C. Cruz and D. Estes. 2007. Rediscovery and phylogenetic placement of Philcoxia minensis (Plantaginaceae), with a test of carnivory. Proceedings of the California Academy of Sciences 58: 447–467
Pereira, C. G., D. P. Almenara, C. E. Winter, P. W. Fritsch, H. Lambers and R. S. Oliveira. 2012. Underground leaves of Philcoxia trap and digest nematodes. Proc. Natl. Acad. Sci. U. S. A. 109: 1–5. doi:10.1073/pnas.1114199109.
Rowland, K. 2012. Hungry plant traps worms underground. Nature (news). doi:10.1038/nature.2012.9757
Scatigna, A. V., V. C. Souza, C. G. Pereira, M. A. Sartori, and A. O. Simoes. 2015. Philcoxia rhizomatosa (Gratioleae, Plantaginaceae): A new carnivorous species from Minas Gerais, Brazil. Phytotaxa 226: 275–280
Scatigna, A. V., Silva, N. G., Alves, R. J. V., Souza, V. C. and O. Simões. 2017. Two New Species of the Carnivorous Genus Philcoxia (Plantaginaceae) from the Brazilian Cerrado. Systematic Botany 42:351-357. doi: 10.1600/036364417X695574
Taylor, P., Souza, V. C., Giulietti, A. M. and R. M. Harley. 2000. Philcoxia: A new genus of Scrophulariaceae with three new species from eastern Brazil. Kew Bulletin 55: 155–163.