Chemical characterization and taxonomic circumscription of Xylopteris argentina (Kurtz) Frenguelli emend. Stipanicic et Bonetti (Corystospermaceae, Triassic, Cacheuta, Argentina)

D`ANGELO J A

La Plata

Simposio; XVI Simposio Argentino de Paleobotánica y Palinología; 2015

Facultad de Ciencias Naturales y Museo (Universidad Nacional de La Plata) y del Museo Argentino de Ciencias Naturales

Coalified compressions and cuticles of Xylopteris argentina (Kurtz) Frenguelli emend. Stipanicic et Bonetti (Corystospermaceae, Triassic Cacheuta, Argentina) are analyzed using semi-quantitative Fourier transform infrared (FTIR) spectroscopy. The main objective is deriving a set of spectrochemical parameters to help refining the taxonomic circumscription of the species, hitherto based on macro and micromorphology. Different IR spectral regions are analyzed: a) aliphatic C-H stretching (3000-2800 cm-1), b) aromatic carbon and oxygen-containing compounds (1800-1000 cm-1), and c) aromatic C-H out-of-plane bending region (900-700 cm-1). The most important functionalities include: alkyl groups in alkyl and aryl ethers and esters, C-O structures in phenols and aryl and alkyl ethers, C-O and O-H in phenoxy structures and ethers, carbonyl (C=O) groups in carboxylic acids and highly conjugated structures (e.g., ketones), and C=C in aromatic structures. Results indicate that compressions and cuticles preserve complementary information. Compressions are mainly characterized by aromatic compounds, showing a high contribution of aromatic carbon bands (e.g., phenoxy compounds). Cuticles exhibit a more aliphatic structure with distinct C=O and some other C-O groups in aliphatic ethers. One-way analysis of variance test (ANOVA) revealed significant differences (p < 0.05) between compressions and their corresponding cuticles regarding the following FTIR ratios: CH2/CH3, CHal/Ox, C=O/C=C, C=O cont, CHar/CHal and CHar/C=C. These IR-derived ratios contain overall structural information on aliphatic, aromatic and oxygen-bearing functional groups. As a result, I propose the aforementioned semi-quantitative, FTIR-derived ratios as spectrochemical-taxonomic parameters for X. argentina. This is a preliminary development for advancing the so far stalled chemotaxonomy/ systematics of the Corystospermaceae.