The present study provides a comprehensive wood microstructure analysis of 16 species of the genus Quercus inhabiting the Himalayan region of India. Indian oaks can be categorised into two groups: Ring porous oaks and diffuse porous oaks. Most of the diffuse porous oaks were quite homogenous in their microstructure and showed slight variations in ray cellular composition and axial parenchyma distribution. The results revealed that the current classification of Quercus is not in concordance with the wood microstructure. From an ecological view point, cluster analysis gave interesting results; largely suggesting that quantitative wood microstructure of Indian oaks is governed by different environmental conditions of eastern and western Himalayas. The genus is also examined from evolutionary point of view. All the species of oaks showed a combination of both primitive and advanced wood anatomical characters.

Wood anatomical features were examined using compound microscope from the permanent slides and macerated samples. The average tangential diameter of vessels was determined from twenty-five measurements taken from transverse section. The frequency of vessels was determined from the average of twenty counts per mm² area. Ten counts were taken for the size of intervessel pits from longitudinal section. The rays per mm is based on an average of ten counts in one mm area in tangential section. Ray height and ray width was based on twenty counts, determined from tangential sections. From the macerated material, fibre and vessel dimensions viz. fibre length, fibre diameter, fibre lumen diameter, fibre wall thickness and vessel length were taken. Twenty-five measurements were taken for fibre characteristics while ten measurements were taken for vessel characteristics. For wood anatomical descriptions, the terminology given by the International Association of Wood Anatomists (IAWA Committee 1989) was followed. The photomicrographs of the sections were taken from the Carl Zeiss Compound light microscope (Scope.A1.Axio) equipped with Carl Zeiss camera. AxioVision Rel 4.0 software was used to capture the microscopic images.

Ecological adaptability of a species described by measurement of mesomorphy (M) and vulnerability index (VI) were calculated by using the following formulas. Vulnerability and mesomorphy were calculated using vessel dimensions including mean vessel frequency. Since vessel frequency is not computed for ring porous species according to the terminology given by IAWA committee (1989) for hardwood identification, hence, only diffuse porous woods were considered here, excluding Q. acutissima and Q. griffithii.

Mesomorphy (M) = Vulnerability x Mean vessel length

Cluster analysis

The average values of different quantitative wood anatomical characters of diffuse-porous oaks, including vessel length, vessel diameter, vessel frequency, inter-vessel pit size, fibre length, fibre diameter, fibre lumen diameter, fibre cell wall thickness, ray height, ray width, cell number and ray per mm (for uniseriate  rays) were subjected to Hierarchical cluster analysis using STATISTICA 7.0. The hierarchical grouping results in formation of a dendrogram which shows a relationship among species that are most similar.