Comparative plastid genomics of Mazaceae: focusing on a new recognized genus, Puchiumazus.

MAIN CONCLUSION: Six Mazaceae plastomes were assembled in this study, including the newly recognized genus, Puchiumazus. Comparative plastid genomic analysis provided new insights into Mazaceae. The phylogenetic categorization of Mazus lanceifolius (Mazaceae) has long been uncertain. In 2021, the scholars Bo Li, D. G. Zhang, and C. L. Xiang republished M. lanceifolius as a new species Puchiumazus lanceifolius, within a new genus Puchiumazus. However, there is little plastome information on Mazaceae. Following the publishing of the new genus Puchiumazus, it is now necessary to study the Mazaceae plastome features to comprehensively understand this young family. The Mazaceae plastomes all have a typical quartile structure. The plastomes have a size ranging from 152,388 to 154,252 bp, and each plastome contains 112 unique genes, including 78 protein-coding genes, 4 rRNA genes, and 30 tRNA genes. A comparative analysis showed that these plastome sequences are highly conserved. Furthermore, we identified four relatively hypervariable regions (trnQ-UUC-psbK, trnS-GCU- trnS-CGA, trnT-UGU-trnL-UAA and ycf1) that can be used as potential DNA barcodes for the identification of this clade. Phylogenetic relationships based on the whole plastome sequences of 25 samples of 14 genera of Lamiales placed M. lanceifolius in the basal clade of the family Mazaceae, with 100% bootstrap support. In summary, the M. lanceifolius results indicate that a new monotype genus (Puchiumazus) should be established at the whole-plastome level. This study provides plastid genomic resources for exploring the phylogeny of Mazaceae.

Rediscovery of Mazus lanceifolius reveals a new genus and a new species in Mazaceae.

Mazus lanceifolius (Mazaceae) is a perennial herb with opposite leaves and endemic to central China that has not been collected for 130 years. Rediscovery of this enigmatic species in the wild allows for determination of its phylogenetic position within Mazaceae. Phylogenetic reconstruction of Mazaceae based on DNA sequences from four plastid markers (matK, rbcL, rps16 and trnL-trnF) and nuclear ribosome ITS consistently showed that Mazus was not monophyletic. Mazus lanceifolius is in the most basal clade within Mazaceae, as sister to the remaining species of three recognized genera Dodartia, Lancea and Mazus. These results support the separation of M. lanceifolius from Mazus as a new genus, which was established here as Puchiumazus Bo Li, D.G. Zhang & C.L. Xiang. Meanwhile, a collection from Shennongjia Forestry District of Hubei Province, China, misidentified as "M. lanceifolius" in previous molecular study, is here revealed to represent an undescribed species of Mazus, i.e., M. fruticosus Bo Li, D.G. Zhang & C.L. Xiang, sp. nov. Morphologically, Puchiumazus is clearly distinct from the other three genera by having quadrangular to somewhat ribbed stems, and obviously opposite leaves. In addition, we provide a taxonomic key to the four genera of Mazaceae.