Abstract
This paper presents the results of the study on pollen morphology of five Polish species of the genus <em>Sorbus</em> L. (<em>S. aria</em> (L.) Crantz, <em>S. aucuparia</em> L. Emend. Hedl., <em>S. chamaemespilus</em> (L.) Crantz, <em>S. intermedia</em> (Ehrh.) Pers. and <em>S. torminalis</em> (L.) Crantz). Observations were carried out with light and scanning microscopes. Investigated pollen grains were small or medium size, most often subprolate or prolate spheroidal in outline. Exine of medium thickness, consisted of two layers. Mainly 3-zonocolporate or sometimes 4-zonocolporate (<em>S. chamaemespilus</em> and <em>S. torminalis</em>) grains were noted. Usually striatae type of sculpture was observed, except the grains of <em>S. intermedia</em>, which were characterized by intermediate type of sculpture, with the features both striate and regulate ornamentation. Pollen morphology of the investigated <em>Sorbus</em> species corresponds with their systematic classification. It is relatively easy to separate pollen grains of the following subgenera: <em>Sorbus</em>, <em>Chamaemespilus</em> and <em>Torminaria</em>. Only subgenus <em>Aria</em> includes grains of different morphology and therefore it is impossible to determine the diagnostic features of this subgenus. Pollen morphology does not confirm a close relationship between <em>S. aria</em> and <em>S. intermedia</em>. It is possible to distinguished pollen grains of all the analysed native species. However, there are no important differences in pollen morphology between the subspecies of <em>Sorbus aucuparia</em>. The key for Polish <em>Sorbus</em> species, based on pollen grain characters is given too.
Highlights
Studies on pollen morphology of European species of the genus Sorbus showed their considerable similarity to pollen grains of other taxa of the Rosaceae family, as Crataegus, Malus, Pyrus, Dryas, Prunus and Aronia (Teppner 1965; Reitsma 1966; Eide 1981; Moore et al 1991, Faegri and Iversen 1992)
Small grains were most often observed in samples of Sorbus aucuparia subsp. aucuparia (60% analysed grains of this taxon) and of S. aucuparia subsp. glabrata (40%) and only sporadically in samples of S. intermedia (2.2%)
The present study reveals completely different types of exine sculpture in those species: striatae type characteristic for grains of S. aria, as mentioned above with the features similar ornamentation of S. aucuparia and intermediate type observed exclusively in grains of S. intermedia
Summary
Studies on pollen morphology of European species of the genus Sorbus showed their considerable similarity to pollen grains of other taxa of the Rosaceae family, as Crataegus, Malus, Pyrus, Dryas, Prunus and Aronia (Teppner 1965; Reitsma 1966; Eide 1981; Moore et al 1991, Faegri and Iversen 1992). The cited author (l.c.) observing pollen of 40 species, originating from western Asia and of Himalayas, distinguished 17 morphological types of grains She recognized shape and size of grains, number, structure and shape of apertures, exine thickness and sculpture type, as diagnostic features of the genus. Within the genus Sorbus, the hybrids and polyploids produce pollen in high percentage sterile
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