This study investigates the nature of trichomes over a large tripinnate frond segment of Odontopteris cantabrica Wagner that is also the index fossil for the Cantabrian Substage (Kosmovian), Late Pennsylvanian age. One objective is methodological, to illustrate the application of micro-FTIR (Fourier transform infrared) spectroscopy to microstructures, and the other one is to document morphology and chemical make-up of trichomes. Significant results reported for the first time from a Carboniferous seed fern include the occurrence of three types of trichomes over the frond, their differentiated cells in terms of color, stomatiferous nature (anomocytic type), and functional-group abundances of trichomes and pinnule cuticles. The trichomes are characterized as being 'fatty', with lower aromaticity, yet distinct aromatic carbon. As inferred from the high CH2/CH3 ratio, aliphatic chains were long and straight, and even less branched than in the pinnule cuticle. Although there are small chemical differences between trichomes and pinnule cuticles, their identity is hypothesized to be very close. In summary, the new information increases the stratigraphic significance of O. cantabrica as a robust index fossil, and supplies significant taxonomic data for separating species in this genus.