Global interest in renewable fuels is rapidly growing with particular emphasis on local energy growth and creating new energy feedstocks, specifically liquid fuel sources. However, the interactive effect of plant species/variety and growth environment on plant structural components, which may influence conversion efficiency and thus play an important role in optimizing the production of biofuels, is not fully understood. In this study cupric oxide (CuO) extractable lignin, which extracts and quantifies lignin-derived monomers, was determined for 25 cultivated and naturalized tropical perennial C-4 grass varieties of napiergrass and Guinea grass that were under assessment for suitability as feedstocks for liquid fuel generation. Principal component analysis of CuO extractable lignin-derived monomers showed differences in composition between napiergrass and Guinea grass, as well as environmental differences within many, but not all napiergrass varieties. Among the samples tested, the greatest differences in lignin composition occurred specifically in vanillyl lignin structures. A wide range (1-2.5) in the ratio of cinnamyl to vanillyl structures (C/V), which often relates to enzymatic degradability in natural systems, was also found. It is expected that the observed CuO lignin differences representing the structure and bonding of lignin will relate to ease of chemical and enzymatic conversion and the effectiveness of pretreatment and conversion in biofuel application. We hypothesize that the C/V ratio of feedstock will positively relate to conversion efficiency and if supported, then compositional lignin metrics such as the C/V ratio could be a predictor to select for more easily degradable biomass for biofuel production. (C) 2015 Elsevier Ltd. All rights reserved.