Pollen morphology of Polish species from the genus Rubus L. (Rosaceae) and its systematic importance

Abstract

The genus Rubus L. (Rosaceae) not been investigated satisfactorily in terms of palynology. This genus is taxonomically very difficult due to the large number of species and problems with their delimitation, as well as very different distribution areas of particular species. The aim of this study was to investigate pollen morphology and for the first time the ranges of intrageneric and interspecific variability of Rubus species, as well as verify the taxonomic usefulness of these traits in distinguishing studied taxa from this genus. The selected species of the genus Rubus were analysed for 11 quantitative pollen characteristics and the following qualitative ones: exine ornamentation, pollen outline and shape, as well as bridge structure. Analyses were conducted on a total of 1740 pollen grains, which represent 58 blackberry species belonging to a majority of subgenera and all the sections and series found in Poland. The most important characters included exine ornamentation (exine ornamentation type, width and direction of grooves and striae, number and diameter of perforations) and length of the polar axis (P). The arrangement of the examined species on the dendrogram does not corroborate division of the genus Rubus into subgenera, sections and series currently adopted in taxonomy. This fact is not surprising because the taxonomy of the genus was not based on pollen characters. Pollen features should be treated in taxonomy as auxiliary, because they fail to differentiate several (10) individual species, while the other ones create groups with similar pollen traits.

Comparison of the Micromorphology and Ultrastructure of Pollen Grains of Selected Rubus idaeus L. Cultivars Grown in Commercial Plantation

“…The thickness of the exine in the grains was lower in ‘Laszka’, ‘Radziejowa’, ‘Pokusa’, and ‘Polka’ were close to the values, but in the case of ‘Polana’ it was in the range of values determined in other Rubus species (0.9–2.4 μm) [ 64 , 73 , 74 , 78 , 79 , 105 ]. Sporopollenin contributes to high exine stability.…”

“…The morphology study of the pollen grains of the six R. idaeus cultivars showed a length of the polar (P) and equatorial (E) axes of P × E: 23.8–29.5 × 21.4–28.6 µm. These values were similar or higher to those described in the literature for R. idaeus and other Rubus species, e.g., R. copelandii , R. helvellicus , R. saxatilis, R. acuminatissimus , R. apricus , R. chrysogaeus , R. clementis , R. diclinis , R. ellipticus , R. ferdinandi-muelleri , R. fraxinifolius , R. gracilis , R. megacarpus , R. montis-wilhelmi , R. niveus , R. novoguineensis , R. papuanus , R. royenii , and R. trigonus [ 60 , 64 , 73 , 74 , 75 ]. The values were lower than those reported for e.g., R. acanthodes , R. alpestris , R. archboldianus, R. buergeri , R. calycinus , R. chamaemorus L., R. lainzii , R. lorentzianus , R. macgregrii , R. moluccanus , R. pectinellus , R. praecox ., and R. seebergensis [ 60 , 64 , 73 , 75 , 78 , 98 , 106 ].…”

“…In other taxa of this genus, the arrangement of striae formed various surface types: loosely striated ( R. acuminatissimus and R. niveus ) , densely striated ( R. copelandii ) , scabrate-striated ( R. lorentzianus ), and papillate-striated ( R. odoratus ). In turn, the surface in R. glaucus was found to be smooth [ 71 , 73 , 75 ]. The pollen grain sculpture in other Rubus taxa exhibited the presence of numerous irregular protuberances forming rugulate ( R. archboldianus ) or scabrate ( R. macgregorii ) surfaces [ 75 ].…”

How much of morphological variability in pollen from genus Rubus L. might be explained by climate variability

“…In this research, among the random effects describing the phylogenetic relatedness of the species studied, the most important ranks were those of subgenus and series, while the least were those of section (Table 4). In contrast, the latest palynological study on Rubus (Lechowicz et al 2020) revealed a low agreement between pollen morphological differentiation and taxonomic division. Pollen traits were most useful at the species level.…”

“…small-sized), with tricolporate or tricolpate pollen grains and mostly striate exine ornamentation (Nazeri 2008;Polyakova and Gataulina 2008;Wrońska-Pilarek and Jagodziński 2011;Wrońska-Pilarek et al 2013, 2019Lechowicz et al 2020). Moreover, intra-generic studies indicated that pollen grains were so similar that usually it was possible to distinguish only a few sections or series and from a few to several individual species, and most often there were groups of taxa with similar pollen characteristics.…”