Estudios en el género Cortaderia (Poaceae). I. Sistemática y nomenclatura de la sect. Cortaderia

The genus Cortaderia (Poaceae) includes 19 South American species, separated into four sections. In this paper the species included in sect. Cortaderia are studied. Cortaderia rudiuscula and C. jubata are two names used with different criteria by diverse authors, which has generated confusion and has led to the frequent determination of herbarium specimens as different species of the section. The original description of C. rudiuscula was written on the basis of four syntypes which belong to more than one species. In this contribution we analyzed type specimens and other herbarium materials assigned to C. rudiuscula, apart from additional plants collected in population samplings for this work, and specimens of the remaining species of the section. A Principal Components Analysis (PCA) was conducted on the basis of characters traditionally used to delimit the species of the section. The analysis showed three morphologic discreet groups that fit to C. araucana, C. selloana and C. speciosa. The lectotype of C. rudiuscula was located among the specimens of C. speciosa, and therefore the synonymy of both species is here proposed. A similar analysis showed that C. jubata represents only a portion of the morphologic variability of C. selloana, and the new combination C. selloana subsp. jubata is proposed. The names C. quila and C. quila var. pygmaeum are reduced to the synonymy of C. speciosa. Cortaderia araucana and C. selloana were originally described as dioecious, and later as gynodioecious. In this paper, populations composed of only pistillate plants (apomyctic) are reported for both species, and, consequently, descriptions are amended to include apomictic populations. A key for the four taxa that are here recognized for the sect. Cortaderia is included, together with descriptions, synonymies and distribution maps.