Mycetia saxicola (Rubiaceae), a new species with cauliflory from limestone areas in Yunnan, China, supported by morphological and molecular data

A new species exhibiting cauliflory within the tribe Argostemmateae (Rubiaceae), <i>Mycetia saxicola</i> Z.Q. Song & D.X. Xu, is described and illustrated from limestone areas in Yunnan, China. Our comprehensive study, which includes literature reviews, field and herbarium morphological observations, and molecular phylogenetic analyses of five plastid DNA regions, reveals that <i>M. saxicola</i> is closely related to <i>M. fangii</i> K.J. Yan & Z.Q. Song. Morphologically, both species share several key features, including cauliflorous inflorescences, few flowers per inflorescence, eglandular bracts and bracteoles, short corolla tubes, and calyx lobes much shorter than the corolla. However, <i>M. saxicola</i> can be readily distinguished from <i>M. fangii</i> by its limestone habitat, subcoriaceous leaves, linear stipules, very short pedicels and peduncles, and a calyx bearing two sessile, deciduous glands on each sinus. Additionally, this paper provides illustrations of six other relevant species of <i>Mycetia</i> to facilitate further taxonomic comparisons.