Chemical and phylogenetic characterization of Guaco (Mikania laevigata; M. glomerata) germplasm

Abstract

Guaco, a native and perennial Brazilian liana, is one of the medicinal plants most widely commercialized in the Brazilian market. The major bioactive compounds in guaco leaves are coumarin and o-coumaric acid, along with kaurene-type diterpenes. Two Mikania species, M. laevigata and M. glomerata, are both treated as guaco in the Brazilian pharmacopeia and are commercialized indiscriminately, although they can be distinguished by the shape of the leaves and by the characteristic coumarin aroma of M. laevigata.We used DNA barcoding, chromosome counting and chemical analysis to study guaco germplasm accessions from collections in 10 Brazilian states. ETS and ITS sequences failed to distinguish most guaco accessions identified as M. glomerata and M. laevigata regardless of geographical origin, suggesting that M. glomerata and M. laevigata are recently diverged species. The chromosome number 2n = 36 was observed in all guaco accessions. In guaco accessions grown under experimental conditions, two chemical phenotypes were found: phenotype G-I, containing moderate coumarin content (644–755 mg/100 g) and high levels of kaurenoic acid (771–881 mg/100 g) and phenotype G-II, containing high levels of coumarin (1123–1309 mg/100 g) and low levels of kaurenoic acid (160–334 mg/100 g). None of the M. glomerata accessions produced coumarin in satisfactory levels (all <100 mg/100 g). Our results suggest that only M. laevigata should be used as guaco. The use of confirmed clonal plant material from controlled sources, such as from a germplasm bank, can guarantee desired pharmaceutical efficacy of this herbal medicine.