A Study of Phenolic Compounds and Their Chemophenetic Value in the Genus Thesium (Santalaceae)

Abstract

Despite the common use of Thesium species as food and medicine and the prevailing systematic (taxonomic) difficulties of the genus, the diversity of phenolic compounds and their chemophenetic value remain largely unknown. As part of ongoing systematic research on Thesium, phenolic compounds and their composition were investigated at four taxonomic ranks: generic, infrageneric, interspecific and infraspecific. Liquid chromatography–mass spectrometry, multivariate analyses, comparisons to DNA data and manual investigations of total ion chromatograms were conducted for 156 samples of 50 Thesium species, as well the two monotypic genera sister to Thesium (Lacomucinea and Osyridicarpos). A wide diversity of phenolic compounds, primarily flavonols, carboxylic acids, phenolic acids and associated derivatives, were observed. Rutin was the most common compound, followed by citric acid, isorhamnetin O-glucoside O-rhamnoside, kaempferol O-rutinoside, quinic acid and cryptochlorogenic acid. Chemophenetic data proved valuable at the generic and interspecific level and, to a lesser degree, at the infraspecific level. On the other hand, no distinct patterns were observed at the infrageneric level, nor did chemophenetic data correlate with infrageneric classifications based on genetic, geographical or morphological data. At the generic level, the patterns of phenolic compounds in Lacomucinea and Osyridicarpos overlapped with those of Thesium species, but no compound or group of compounds were unique to Thesium. At the interspecific level, total ion chromatograms of the species were largely distinct from one another and, with the exception of four species, remarkably consistent. Two related species (T. triflorum and T. scandens) with doubtful species boundaries had similar but distinct chromatograms, providing evidence of their retention as separate species. At the infraspecific level, the data were mostly inconclusive, but variation in samples of T. asterias revealed two morphologically distinct populations, one of which is possibly a species new to science. This study provides valuable preliminary insights into the phenolic diversity and chemophenetic relationships in Thesium, Lacomucinaea and Osyridicarpos and highlights the potential of chemophenetics in taxonomically problematic plant groups.