| Summary: | The taxonomy of <i>O. dichroantha</i>, <i>O. nervosa,</i> and their allied species is extremely controversial among authors. The delimitation of these species was extremely confusing, and closely related species were separated by weak and non-diagnostic morphological traits. A taxonomic revision of these taxa is presented here based on our fieldwork and a thorough study of herbaria specimens. The species <i>O. dichroantha</i> and <i>O. sharifii</i> are regarded as synonyms of <i>O. setosa</i>, and <i>O. maculata</i> is reduced to synonymy with <i>O. nervosa</i>. In addition, the typification of accepted names and relevant synonyms, detailed morphological descriptions and brief comments on the relationships between species are provided. Besides, it is accentuated that the introduction of any new species should be based on complete evidence to avoid systematic complexity. The results of this study play an important role in solving the problems of plant diversity and in the conservation of plant diversity.
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