Diaporthe is an important plant pathogenic genus, which also occurs as endophytes and saprobes. Many Diaporthe species that are morphologically similar proved to be genetically distinct. The current understanding of Diaporthe taxonomy by applying morphological characters, host associations and multi-gene phylogeny are problematic leading to overestimation/underestimation of species numbers of this significant fungal pathogenic genus. Currently, there are no definite boundaries for the accepted species. Hence, the present study aims to re-structure the genus Diaporthe, based on single gene phylogenies (ITS, tef, tub, cal and his), multi-gene phylogeny justified by applying GCPSR (Genealogical Concordance Phylogenetic Species Recognition) methodology as well as the coalescence-based models (PTP—Poisson Tree Processes and mPTP—multi-rate Poisson Tree Processes). Considering all available type isolates of Diaporthe, the genus is divided into seven sections while boundaries for 13 species and 15 species-complexes are proposed. To support this re-assessment of the genus, 82 Diaporthe isolates obtained from woody hosts in Guizhou Province in China were investigated and revealed the presence of two novel species and 17 previously known species. Synonymies are specified for 31 species based on molecular data and morphological studies. Dividing Diaporthe into several specific sections based on phylogenetic analyses can avoid the construction of lengthy phylogenetic trees of the entire genus in future taxonomic studies. In other words, when one conducts research related to the genus, only species from the appropriate section need to be selected for phylogenetic analysis.