We provide a general introduction to the prodromi to Flora Costaricensis, and an introduction to the precursors of subtribe Pleurothallidinae. We present a systematic revision of the genus Echinosepala for the flora of Costa Rica and a detailed discussion of molecular evidence with regard to most Costa Rican taxa, aimed at phylogenetically framing Echinosepala within the subtribe Pleurothallidinae, recognizing internal relationships among the species in the genus, and proposing evolutionary hypotheses. We recognize 10 species of Echinosepala in Costa Rica. Each species is described and illustrated with one or more botanical drawings and photographs, all based on Costa Rican material. Etymology, distribution, ecology, distinguishing features, and affinities with other taxa in the genus are discussed, taxonomic notes are provided, and a list of selected material examined for this study is included for each taxon. Two new species of Echinosepala, E. glenioides and E. isthmica, are described and illustrated, and their relationships are discussed. New combinations are proposed in Echinosepala for Pleurothallis alexandrae and P. pastacensis, and the former species is neotypified.