Due to overlapping in several of the primary pollen morphological attributes (viz. aperture type and exine sculpturing) throughout the subfamilies and tribes of Rubiaceae, these attributes are less important for delineating the majority of the taxa at subfamilial and tribal levels than at generic and specific levels. This in turn creates difficulties in the identification of rubiaceous pollen grains in various palynological studies. In such cases, where the two major pollen morphological attributes (apertural type and exine ornamentation pattern) are more or less common, we intended to explore whether an additional pollen morphological character could reliably be used in the demarcation of taxa. The present work deals with the pollen morphological details of 17 species of Rubiaceae from the Darjeeling and Arunachal Himalayas. This eurypalynous family exhibits a wide array of pollen morphological attributes, particularly aperture type, exine ornamentation pattern and variable sculpturing on colpus membrane. Principal component analysis (PCA) was performed to determine the major pollen morphological variables responsible for delimiting the studied species; this analysis indicated that variation in colpus membrane ornamentation (psilate, granulate, scabrate, verrucate) is a key attribute in characterizing the studied eastern Himalayan rubiaceous taxa to generic and specific levels.

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