This dissertation is a taxonomic study of 14 species of the genus Calamagrostis section Deyeuxia described under subsection Stylagrostis (Mez) Escalona, and an appendix list of other species presenting a stipitate lemma;The treatment for each species includes a description, synonymy, discussion, illustrations, and distribution data. Three new species are described; Calamagrostis cleefii Escalona, Calamagrostis guamanensis Escalona, and Calamagrostis ramonaea Escalona. The remaining eleven species are revised;There are about 70 species of the genus Calamagrostis inhabiting the paramos in the Andes of Venezuela, Colonbia, Ecuador, and Peru, and the puna of Peru, Bolivia, Chile, and Argentine. The lowland species inhabit southeastern Argentina, Uruguay, Paraguay, and Brazil;Subsection Stylagrostis is based on anatomical, morphological, and ecological characters, and the possible evolution of the species included in the present study;Descriptions of the leaf epidermis, and transverse sections of the lamina, and their taxonomic implications, are presented. The species were segregated using cladistic and numerical analyses considering morphological (external, internal, microscopic), ecological, and distributional characters (habitat, geographical distribution), and character states to produce a cladogram indicating relationships among the species. One character state "lemma stipitate below the callus." was used to interpret this subsection as a monophyletic;Numerical and cladistic analyses were used to clarify species and relationships, within subsection Stylagrostis. Detailed descriptions and keys are provided to identify the species within subsection Stylagrostis;The appendix lists other species with stipitate florets, that belong to subsection Stylagrostis but distributed in different geographic region (south Andes of Chile and Argentina and lowlands of Brazil, Uruguay, Paraguay) which will be considered in future publications.