Pollen morphology and systematic significance of some Onosma L. species (Boraginaceae) distributed in pan Himalayan regions

Abstract

The pollen morphology of 15 Onosma L. species has been examined by SEM for the first time from Pan Himalayan regions of Pakistan and China. Generally, the pollen grains are single, isocolpate, radially symmetrical, isopolar or heteropolar, 3-colporate or 3syncolporate, small to medium in size. The mean polar axis ranged from 10.00-25.43 µm long while the equatorial diameter ranged from 8.68-16.93 µm. The mean P/E ratio generally ranged from 1.04-1.56 µm. On the basis of P/E ratio, three pollen shapes have been recognized (prolate spheroidal, subprolate and prolate). Ornamented aperture membrane and lolongate ora uniformly observed among all studied taxa. However, the results show great diversity within species in regard of polarity, apertures and exine ornamentation (spinulose, rugulate, rugulate-echinate, rugulate to granulate). On the basis of aperture type, two basic pollen types have been recognized. Type-I 3-syncolporate observed in five species (O. confertum, O.