African C3 grass n-alkane distributions & plant chemotaxonomy

• Existing proxies are ill-suited to reconstruct grassy African C 3 ecosystems. • C 3 PACMAD grasses produce exceptionally high abundances of long-chain n- alkanes, and thus measuring and reporting the C 35 n -alkane is important. • C 3 grass n -alkane distributions are influenced by both phylogeny and physiology. • n -Alkane distributions are a potential C 3 grass paleoproxy in sedimentary archives. Reconstructing past vegetation can elucidate the timing, climate forcings, and biotic mechanisms of ecosystem change. Plant macro- and microfossils are traditionally used to study past vegetation but suffer from production and taphonomic biases, such as underrepresentation of important herbaceous vegetation components. Geochemical proxies can fill this gap, but carbon isotopes (δ 13 C) in isolation are unable to distinguish between structurally different C 3 habitats, such as forests and grasslands. Thus, new geochemical methods to identify grassy C 3 ecosystems are necessary. We present n -alkane chain length distributions of 209 plant specimens from two Kenyan C 3 -dominated ecosystems, representing a wide range of plant functional types (PFTs). We find that C 3 PACMAD grasses produce exceptionally high abundances of long chain C 33 and C 35 n -alkanes (ACL = 32.7, mean C 33 + C 35 relative abundance = 0.69), unlike other C 3 PFTs which produce low abundances of C 33 and C 35 (ACL = 28.9–30.3, mean C 33 + C 35 relative abundance = 0.0–0.21). This finding highlights the importance of measuring and reporting the C 35 n -alkane. Our data further demonstrate that n -alkane distributions can serve as a proxy for some African C 3 PACMAD grasses, offering a new paleoecological tool for distinguishing C 3 vegetation types.