Pollen Micro-morphology of the Minuartia Species (Caryophyllaceae) in Iran

The present study compared pollen micro-morphological characters among 20 Iranian Minuartia species. For this purpose, mature pollen grains taken from unopened flowers, were prepared, fixed and exhaustively investigated using Scanning Electron Microscopy (SEM). In order to perform the pollen micro-morphology of Minuartia, and to find its significance in taxonomy of the group, qualitative and quantitative variables related to the shape, size, ornamentations and pores were studied. Cluster and PCA analyses of qualitative and quantitative data were performed to demonstrate the pollen grain similarities among the species. According to our results, Minuartia species exhibit either sub-spherical or polyhedral pollen shapes. Pollen size also varies among different species. The longest polar axis length (P) belongs to Minuartia meyeri Bornm. (34.3±0.26µm) and the smallest one to M. montana L. (15.8±0.26µm). Pore ornamentations differ from prominent granular to slightly or distinctly sunken granular. The number of pores also varies considerably depending on species. It ranges from 10 (in M. meyeri and M. acuminata Turrill) to 24 (in M. subtilis Hand.-Mazz.) on two pollen hemispheres. The most reliable characters in this study were pore diameter (annulus included) (D), equatorial diameter (E), polar axis length (P), the distance between two pores (d), pollen outline, Pore diameter (annulus excluded) (R), annulus diameter (a), P/E ratio, Puncta diameter and Echini diameter respectively. Echini vs puncta (Ec:Pu) diameter ratio appeared to be crucial for the distinction of some closely related species such as M. sublineata Rech.f. and M. lineata (Boiss.) Bornm., as well as M. montana and M. sclerantha (Fisch & C. A. Mey.) Thell. Moreover, three out of the 20 species have D: d ratio (pore diameter: the distance between two pores ratio) only ≥ 1µm. According to our results, some differences in quantitative and qualitative palynological characters of similar species were observed that could be useful. Despite the diagnostic value of palynological data at the species rank, it was not useful to circumscribe any taxonomic group at the higher ranks.