Palynological Characterization and Taxonomic Delimitation of the Genus Impatiens L. in Pakistan: An LM and SEM Study.

Impatiens L. is a taxonomically complicated genus of flowering plants that entails extensive morphological studies to demarcate its taxa. In order to assess the systematic value of pollen morphology, we collected 14 Pakistani taxa (12 species and 2 sub-species) of the genus Impatiens. The qualitative and quantitative elements of the pollen were meticulously studied using light microscopy (LM) and scanning electron microscopy (SEM). All Pollen of Pakistani balsams are stenopalynous and are 4-aperturate, except Impatiens meeboldii, which is 2-aperturate. The pollen are usually small to medium-sized. The largest and smallest pollen grains in equatorial view were observed in I. flemingii (38.75-42.25 μm) and I. lemannii subsp. lemannii (13.75-20 μm) respectively. Oblate pollen are more frequent (57%), whereas sub-oblate (14%), oblate-spheroidal (7%), per-oblate (7%), spheroidal (7%), prolate-spheroidal (7%), and sub-prolate (7%) are also present. The general outlines in the polar view are mostly rectangular (57%), whereas the elliptic (57%) outline is more common in the Equatorial view. Exine ornamentation is more commonly reticulate (71%), while micro-reticulate (21%) and gemmate to slightly clavate (7%) are also present. There is much variation found in the features of muri and lumina. Muri are mostly polygonal, ranging from 3-4 angled to 4-8 angled, except I. bicolor subsp. pseudo-bicolor, in which the muri show gemmate to clavate ornamentation. Exine thickness also varies; the smallest exine thickness is observed in I. balfourii (0.25-0.75 μm), and the largest exine thickness is observed in I. sulcata (2.25-3.75 μm). The lengths of colpi show variation; the smallest colpi lengths were observed for I. bicolor subsp. pseudo-bicolor (5.12-7.93 μm) and I. edgeworthii (7.68-7.93 μm) whereas the largest colpi length was observed in I. bicolor subsp. bicolor (8.96-15.36 μm) and I. lemannii subsp. kurramensis (6.4-15.36 μm). A taxonomic key was created based on the pollen features, emphasizing the differences among the various taxa. UPGMA hierarchical clustering and Principal Component Analysis (PCA) were used to group the taxa into specific clusters and components, showing significant variation in pollen morphology among different species. This thorough analysis highlights the usefulness of palynological traits in classifying and studying the evolution of the Impatiens genus in Pakistan.