Moroccan citron
The Moroccan citron was described by the Moroccan professor Henri Chapot, as being a sweet citron, meaning that its pulp is low in acid. He discovered that the acidity in the more common citrons or lemons, is represented by red on the inner coat of seeds specifically on the chalazal spot, violet pigmentation on the outer side of the flower blossom, and also by the new buds that are reddish-purplish. The Moroccan citron which is acidless is completely lacking the red color. This designation was cited by Herbert John Webber and Leon Dexter Batchelor the editors of the fundamental treatise on citrus, namely The Citrus Industry, which was published by the University of California, Riverside in 1967.
Citrus taxonomy
The trifoliate orange is a cold hardy plant distinguishable by its compound leaves with three leaflets and its deciduous nature, but is close enough to the genus "Citrus" to be used as a rootstock. Swingle moved the trifoliate orange from "Citrus" to its own genus, "Poncirus". It was long thought to be the only member of this genus, until a second species, "Poncirus polyandra", was discovered in Yunnan (China) in the 1980s. Early phylogenetic analysis nested "Poncirus" within the citrus, suggesting they all belong to a single genus, but the genomic sequencing of Wu, "et al.", placed it outside the cluster representing "Citrus", and the authors retained a separate "Poncirus" genus.