Pollen morphology ofXanthiumL. (s.l.) (Asteraceae, Asteroideae, Heliantheae, Ambrosiinae) in the Iberian Peninsula-a palynotaxonomic approach to a poisonous, allergenic and invasive genus

The pollen morphology of the Iberian taxa of the genusXanthiums.l. and of the non-Iberian speciesX. ambrosioideswas studied to help to identify these poisonous, allergenic and invasive taxa and clarify their taxonomic relationships. In addition, the question of the existence and structure of a mesoaperture in the apertural system ofXanthiumwas also considered. The pollen grains of sectionsAcanthoxanthiumandXanthiumclearly differ by their characters, which supports the separation of both taxa and allows for their distinction based on pollen morphology. It is suggested that the morphological and palynological differences betweenXanthiumandAcanthoxanthium, together with the lack of hybridisation between the two sections and the monophyly ofAcanthoxanthium, could lead to the elevation of the latter to the generic status. The two species of sectionXanthiumpresent in the Iberian Peninsula (X. orientaleandX. strumarium) and of sectionAcanthoxanthiumare well separated by their palynological features. Likewise, the Iberian subspecies ofXanthium, X. orientalesubsp.orientaleandX. orientalesubsp.italicumare palynologically distinguishable. However, no significant difference could be found between the pollen ofX. strumariumsubsp.strumariumand ofX. strumariumsubsp.brasilicum. The pollen data do not support the hypotheses of a hybrid origin forX. strumariumsubsp.brasilicum. A mesoaperture intersecting the foot layer and the upper part of the endexine is present in both sections, which is congruent with the results already found for other Asteroideae.

Automated summary

The study of pollen morphology of the Iberian taxa of the genus Xanthiums.l. and of the non-Iberian species X. ambrosioides provides insights into identifying these toxic, allergenic, and invasive taxa and clarifying their taxonomic relationships. Additionally, the presence of a mesoaperture in the apertural system of Xanthium was considered. The differences in pollen grains support the separation of sections Acanthoxanthium and Xanthium, suggesting a potential elevation of Acanthoxanthium to the generic status.