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.

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.

[4][5] Members of the genus are small perennial or annual herbs that reside in oases of deep white sand surrounded by the typical vegetation of the cerrado ecoregion.

Peter Taylor et al. later noted in the 2000 description of the genus that its affinities should include the genera Gratiola and Dopatrium in the tribe Gratioleae of the Scrophulariaceae.

In 2004, E. Fischer also placed in tribe Gratioleae, but also placed it within the informally recognized subtribe Dopatriinae, which was described as also containing the genera Deinostema, Dopatrium, Hydrotriche, and Limnophila, which consist mostly of aquatic species.

In 2007, an extensive study and phylogenetic analysis by Peter Fritsch et al. confirmed that Philcoxia should be placed in the tribe Gratioleae, but it is in fact not as closely related to Gratiola and the Dopatriinae as was previously assumed.

[6] The first recognized specimens of Philcoxia (P. bahiensis) were collected by local resident Wilson Ganev in August 1992 from the Serra do Atalho in the municipality of Piatã of Bahia.

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.

[4][5] 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.