Pollen morphology of endemic species Pimpinella serbica (family Apiaceae)

Abstract

Introduction: Pimpinella serbica (Vis.) Benth. & Hook., belonging to the Apiaceae, is native to the central and western parts of Balkans (Bosnia and Herzegovina, Montenegro, North Macedonia, Serbia) and Albania. It prefers limestone habitat at an average altitude of about 1300 m forming plant communities with other mountainous species, such as spruce and Greek maple (Pancicii-Aceri heldreichii-Piceetum). In Serbia it inhabits mountains such as Kopaonik, Stara planina, Zlatar, Javor, etc. Objective: The pollen morphology of P. serbica, Balkan endemic species distributed in Serbia, were examined by scanning electron microscopy (SEM) in order to contribute the morphological, taxonomic and melissopalynological studies. Materials & methods: The umbels were collected from wild plant populations at full flowering stage. A set of three mounted and labelled voucher specimens were processed in standardized way and deposited in the herbarium collection of the Faculty of Agriculture, University of Belgrade. For SEM study the pollen grains were covered with gold (in BAL-TEC SCD 005 Sputter Coater, 100 seconds in 30 mA) and observed using JEOL JSM- 6390 LV electron microscope at an acceleration voltage of 20 kV. Pollen grains were imaged in polar and equatorial view, and observations and measurements were done on a sample of 30 grains for each morphological character. The following taxonomically significant features describing pollen grains were examined: size, shape, exine sculpture, apertures, polarity, symmetry, equatorial (E) and polar (P) axes length, and apocolpium index. Results: The pollen grains of P. serbica are isopolar, radially symmetrical and small-sized (Figure 1a). The ratio between the polar axis length (P = 21.5 ± 0.8 μm) and the equatorial diameter (E = 12.9 ± 0.9 μm) of 1.7 ± 0.2 indicates prolate shape (Figure 1b). The grains are slightly equatorially expanded with obtuse polar caps, and triangular in polar view with interangular furrows (Fig 1c). The grains have tricolporate apertures with three straight sunken ectocolpi arranged regularly meridionally, of mean length 17.7±0.9 μm, each one with endopore positioned in the indentations between the mesocolpial lobes. Mesocolpial width is 7.3±1.8 μm. Apocolpium index amounts 0.39±0.04. The exine was found to have rugulate sculpture (Figure 1d). Conclusion: Polen grains of P. serbica have typical form for Apiaceae family, but some fine details provided by the current study could help in intrageneric differentiation contributing to taxonomic research. The analyzed palynomorphological characteristics may be of special importance for estimating geographical origin of honey, considering this species limited distribution area. The results revealed that exine ornamentation could be a diagnostic trait taxonomically significant and useful for identification to species level