Additions to the flora of the Czech Republic. XXI.

This twenty-first part of floristic contributions summarises data on taxa newly discovered in the Czech Republic – the undescribed hawkweed hybrid of Pilosella officinarum × P. scandinavica, three brambles species (the endemic Rubus atroroseus, the newly described R. lobifolius and the newly distinguished R. subgothicus) and the first data of Symphytum ×wettsteinii (S. officinale × S. tuberosum) in the Czech Republic. Records of alien species found in the country for the first time (Alopecurus rendlei, Cyperus congestus, Euphorbia saratoi, Potentilla pensylvanica and others) and taxa newly escaped from cultivation (Aristolochia macrophylla, Hibiscus syriacus, Symphytum ×hidcotense and Teucrium hircanicum) are also listed. Furthermore, critically threatened species (according to the Red List of Vascular Plants of the Czech Republic) are reported from new localities (e.g. Anacamptis pyramidalis, Asplenium scolopendrium, Carex capillaris, Catabrosa aquatica, Diphasiastrum tristachyum, Epipactis pontica, Himantoglossum adriaticum, Juncus gerardii, Littorella uniflora, Ventenata dubia, Veronica opaca and Viola alba). Finally, less rare and threatened species are reported from phytogeographical districts where they have not been recorded before (Aconitum variegatum, Aira praecox, Carex bohemica, Knautia drymeia and Nasturtium officinale).