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Philcoxia is a genus of seven rare plant species in the Plantaginaceae that are endemism to Brazil and resemble terrestrial species of the genus Utricularia. The genus, formally described in 2000, consists of the species P. bahiensis, P. goiasensis, P. minensis, P. tuberosa, P. rhizomatosa, P. maranhensis and P. courensis, each of the first three named for the Brazilian state to which it is endemic. The species are characterized by subterranean stems, leaf shape leaves at or below the soil surface, and five-lobed calyces. Their habitat has been reported as areas of white sand in the midst of cerrado vegetation at an elevation between 800 and 1450 m. Initial descriptions of the genus included suspicions that the plethora of stalked capitate glands on the upper surfaces of leaves was an indication that these species may be carnivorous. A study published in 2007 tested P. minensis for protease activity, a typical test for the carnivorous syndrome, and could detect none. Later studies detected other digestive enzymes such as and qualitatively assessed prey digestion and nutrient uptake, suggesting that it is a true carnivorous plant. The genus epithet honors David Philcox (1926-2003), a botanist at Kew Gardens who worked extensively in tropical Scrophulariaceae.Fritsch, P.W., Almeda, F., Martins, A.B., Cruz, B.C., and Estes, D. (2007). Rediscovery and phylogenetic placement of Philcoxia minensis (Plantaginaceae), with a test of carnivory. Proceedings of the California Academy of Sciences, Fourth Series, 58(21): 447-467.Taylor, P., Souza, V.C., Giulietti, A.M., and Harley, R.M. (2000). Philcoxia: A new genus of Scrophulariaceae with three new species from Eastern Brazil. Kew Bulletin, 55(1): 155-163.
However, an even earlier specimen now recognized as P. goiasensis had been collected in 1966 near Posse in the northeastern state of Goiás by a group from the New York Botanical Garden. Initially, the specimen had been determined to be a member of the Lentibulariaceae. Peter Taylor and David Philcox later concluded that this represented an undescribed genus of Scrophulariaceae. A description and illustration was completed and set aside for over twenty years. Then, in 1994, Taylor showed the specimen and description to Ray Harley in preparation for publication. Harley, who had been involved in the early 1990s discovery of P. bahiensis, recognized Taylor's materials as another species of the as yet undescribed genus.
Peter Fritsch and his coauthors decided to do a more comprehensive test for carnivory on P. minensis after they observed nematode worms on leaf surfaces. The similarity between the habitat for Philcoxia species and that of Genlisea and their similar subterranean leaves and stems spurred the team's decision to test for potential carnivory in the field and in situ. They tested for a protease enzyme that is one of the enzymes found in other carnivorous plants and is responsible for breaking down captured prey. They hypothesized that Philcoxia could be carnivorous, capturing nematodes and possibly soil microbes like Utricularia and Genlisea do. Ultimately, Fritsch's study concluded that while no protease activity was detected, this fact does not rule out the possibility that the genus may be carnivorous in some other way. They note that there are many possibilities, such as seasonal carnivory or the unusual growth form being an adaptation to the heat and sun, and more study is needed before precise conclusions can be reached.
A study by Caio G. Pereira et al. published in 2012 provided experimental evidence using 15N-labeled nematodes, concluding that P. minensis actively digests prey and absorbs the nutrients. This data was combined with the observation that the leaf surfaces of P. minensis produce , similar to many other carnivorous plants.Pereira, CG, DP Almenara, CE Winter, PW Fritsch, H Lambers, and RS Oliveira. 2012. Underground leaves of Philcoxia trap and digest nematodes. Proc. Natl. Acad. Sci. USA, published online ahead of print. The similarity in structures in all the species of this genus suggest that all species are carnivorous.
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