Abstract
The pollen morphology was studied of 24 Salix species native to Poland, which represented two subgenera, 17 sections and five subsections occurring in Poland. The aim of this study was to discover the taxonomical usefulness of the pollen features under analysis, and to investigate the ranges of their interspecific variability. In total, 720 pollen grains were studied. They were analysed with respect to seven quantitative features (length of the polar axis ˗ P, equatorial diameter ˗ E, length of the ectoaperture ˗ Le, exine thickness ˗ Ex, and P/E, Ex/P and Le/P ratios) and the following qualitative ones: pollen outline and exine ornamentation. The most important features were exine ornamentation (muri, lumina and margo) characters. The pollen features should be treated as auxiliary because they allowed to distinguish eight individual Salix species, and five groups of species. Statistical analysis of the studied traits indicated a high variability among the tested species. The most variable biometric features were P, E and Le, while lower variability occurred in P/E, Le/P and d/E.
Highlights
The genus Salix L. (Salicaceae) consists of deciduous trees and shrubs, including dwarf forms, with decumbent shoots, mainly distributed across the cold and moderate climate zones of the Northern Hemisphere
The taxa under examination represented all three subgenera, all sections (17) and subsections (5) of willows found in Poland, including two legally protected species in Poland–S. lapponum and S. myrtilloides
The small-sized class of pollen prevailed in 20 Salix species, including 13 species (S. alba, S. aurita, S. hastata, S. alpina, S. pentandra, S. phylicifolia, S. purpurea, S. repens, S. reticulata, S. rosmarinifolia, S. silesiaca, S. triandra, and S. viminalis) with only small-sized pollen grains
Summary
The genus Salix L. (Salicaceae) consists of deciduous (and, rarely, semi-evergreen) trees and shrubs, including dwarf forms, with decumbent shoots, mainly distributed across the cold and moderate climate zones of the Northern Hemisphere. There are 65 willow species described in Europe, including 27 which are native to Poland [6, 7]. Salix is considered one of the most taxonomically difficult plant genera and its infrageneric taxonomy is still in progress. It is a result of, among others, a very simplified and undifferentiated flower structure, which limits the use of generative traits in Salix systematics. Many Salix species exhibit significant morphological variations, correlated with high infraspecific genotypical polymorphisms.
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