Phosphoenolpyruvate carboxylase (PEPC) gene family plays a crucial role in both plant growth and response to abiotic stress. Approximately half of the Orchidaceae species are estimated to perform CAM pathway, and the availability of sequenced orchid genomes makes them ideal subjects for investigating the PEPC gene family in CAM plants. In this study, a total of 33 PEPC genes were identified across 15 orchids. Specifically, one PEPC gene was found in Cymbidium goeringii and Platanthera guangdongensis; two in Apostasia shenzhenica, Dendrobium chrysotoxum, D. huoshanense, Gastrodia elata, G. menghaiensis, Phalaenopsis aphrodite, Ph. equestris, and Pl. zijinensis; three in C. ensifolium, C. sinense, D. catenatum, D. nobile, and Vanilla planifolia. These PEPC genes were categorized into four subgroups, namely PEPC-i, PEPC-ii, and PEPC-iii (PTPC), and PEPC-iv (BTPC), supported by the comprehensive analyses of their physicochemical properties, motif, and gene structures. Remarkably, PEPC-iv contained a heretofore unreported orchid PEPC gene, identified as VpPEPC4. Differences in the number of PEPC homolog genes among these species were attributed to segmental duplication, whole-genome duplication (WGD), or gene loss events. Cis-elements identified in promoter regions were predominantly associated with light responsiveness, and circadian-related elements were observed in each PEPC-i and PEPC-ii gene. The expression levels of recruited BTPC, VpPEPC4, exhibited a lower expression level than other VpPEPCs in the tested tissues. The expression analyses and RT-qPCR results revealed diverse expression patterns in orchid PEPC genes. Duplicated genes exhibited distinct expression patterns, suggesting functional divergence. This study offered a comprehensive analysis to unveil the evolution and function of PEPC genes in Orchidaceae.

Dendrobium tetrapterum, a cryptic species in the D. lindleyi alliance, is described and illustrated. Detailed morphological comparisons indicate that it is similar to D. lindleyi and D. jenkinsii but can be distinguished by four morphological characters, namely petals without (vs. with) claw, slit (vs. entire) transverse septum at lip base, anther cap with (vs. without) indentation on each side and a rhombic (vs. pentagonal–octagonal or oblong) pseudobulb cross-section. Combined with the geographical distribution and whole plastid genome data, we confirm that D. tetrapterum is not a natural hybrid of the other two species, but a separate species.

The taxonomic status of Hayata Aver. has long been a subject of debate, with confusion and uncertainty regarding its relationship to Zeuxine Lindl. and Cheirostylis Blume. Here, we conducted phylogenetic analyses using complete plastome data and a combination of traditional molecular markers (nrITS, matK, psaB, rbcL and trnL-trnF). Both plastid and nuclear datasets consistently resolved Hayata as sister to Zeuxine, with strong support from plastid data and moderate support from nrITS. Our results support the recognition of Hayata as an independent genus, distinct from both Zeuxine and Cheirostylis.