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Collecting species-level information on plant functional traits is highly relevant for understanding ecosystem functioning under global change. Measuring optical properties of plant species is a promising approach to retrieve such data, but standardized protocols are essential. Due to fine-scale heterogeneity of many vegetation types, measuring the spectral response, as a proxy for functional traits, of individual plant species remains challenging using conventional approaches. Here we present a novel method for measuring the reflectance of individual species in situ. The procedure consists of measuring monospecific arrangements of plant individuals on a black, light absorbing table, preserving structural plant properties while avoiding the admixture of other species, soil or non-photosynthetically active vegetation. To evaluate the feasibility of the approach, a case study was conducted on forbs, where we collected and compared the reflectance of 16 herbaceous species at different phenological stages, both using common field spectroscopy and by following our novel procedure. Our procedure accurately represented spectral and functional differences between species. Spectral shape, and to a lesser extent, amplitude differences between species were preserved (SAM: Mantel r = 0.69 and p = 0.001; Manhattan distance: Mantel r = 0.42 and p = 0.002). Moreover, the method was able to capture the pattern of functional traits present among the sampled species (Procrustes r = 0.81 and p = 0.001). The new method is promising for building databases of plant traits based on spectral libraries. It might, moreover, form a standardized procedure for field campaigns, especially in the context of mixed grasslands and forb systems where relatively small plants dominate the ecosystem.