  We investigate the distribution of flavonoids, a major category of plant
secondary metabolites, across species. Flavonoids are known to show high
species specificity, and were once considered as chemical markers for
understanding adaptive evolution and characterization of living organisms. We
investigate the distribution among species using bipartite networks, and find
that two heterogeneous distributions are conserved among several families: the
power-law distributions of the number of flavonoids in a species and the number
of shared species of a particular flavonoid. In order to explain the possible
origin of the heterogeneity, we propose a simple model with, essentially, a
single parameter. As a result, we show that two respective power-law statistics
emerge from simple evolutionary mechanisms based on a multiplicative process.
These findings provide insights into the evolution of metabolite diversity and
characterization of living organisms that defy genome sequence analysis for
different reasons.
