The reflectance of a canopy of mixed species may be affected, among other things, by the percentage cover of each species or by the proportion of each species in the total biomass. The likelihood of either property affecting reflectance is greatest when two species are differentiable spectrally and spatially as is the case for the species of grass and clover that are common in pasture in the U.K. This Letter examines the relations of the percentage cover of clover with reflectance and the proportion of clover in the total biomass with reflectance for a field of pasture in Belper in Derbyshire, U.K. using partial correlation analysis.