Catalogue of alien plants of the Czech Republic (2nd edition): checklist update, taxonomic diversity and invasion patterns.
A complete list of all alien taxa ever recorded in the flora of the Czech Republic is presented as an update of the original checklist published in 2002. New data accumulated in the last decade are incorporated and the listing and status of some taxa are reassessed based on improved knowledge. Alien flora of the Czech Republic consists of 1454 taxa listed with information on their taxonomic position, life history, geographic origin (or mode of origin, distinguishing anecophyte and hybrid), invasive status (casual; naturalized but not invasive; invasive), residence time status (archaeophyte vs neophyte), mode of introduction into the country (accidental, deliberate), and date of the first record. The Czech alien flora consists of 350 (24.1%) archaeophytes and 1104 (75.9%) neophytes. The increase in the total number of taxa compared to the previous catalogue (1378) is due to addition of 151 taxa and removal of 75 (39 archaeophytes and 36 neophytes), important part of the latter being the reclassification of 41 taxa as native, mostly based on archaeobotanical evidence. The additions represent taxa newly recorded since 2002 and reported in the national literature; taxa resulting from investigation of sources omitted while preparing the previous catalogue; redetermination of previously reported taxa; reassessment of some taxa traditionally considered native for which the evidence suggests the opposite; and inclusion of intraspecific taxa previously not recognized in the flora. There are 44 taxa on the list that are reported in the present study for the first time as aliens introduced to the Czech Republic or escaped from cultivation: Abies concolor, A. grandis, A. nordmanniana, Avena sterilis subsp. ludoviciana, A. × vilis, Berberis julianae, B. thunbergii, Bidens ferulifolius, Buddleja alternifolia, Buglossoides incrassata subsp. splitgerberi, Buxus sempervirens, Corispermum declinatum, Cotoneaster dielsianus, C. divaricatus, Euphorbia myrsinites, Gleditsia triacanthos, Helleborus orientalis, Hieracium heldreichii, Koelreuteria paniculata, Lonicera periclymenum, Lotus ornithopodioides, Malus baccata, M. pumila, Miscanthus sacchariflorus, Morus alba, Muscari armeniacum, Paeonia lactiflora, Pennisetum alopecuroides, Pinguicula crystallina subsp. hirtiflora, P. grandiflora subsp. rosea, Podophyllum hexandrum, Pyracantha coccinea, Rhodotypos scandens, Rumex patientia × R. tianschanicus 'Uteuša', Salix cordata, Sarracenia purpurea, Sasa palmata 'Nebulosa', Scolymus maculatus, Spiraea japonica, Tagetes tenuifolia, Thuja occidentalis, Trifolium badium, Vaccinium corymbosum and Viburnum rhytidophyllum. All added and deleted taxa are commented on. Of the total number of taxa, 985 are classified as casuals, 408 as naturalized but not invasive, and 61 as invasive. The reduction in the number of invasive taxa compared to the previous catalogue is due to a more conservative approach adopted here; only taxa that currently spread are considered invasive. Casual taxa are strongly over-represented among neophytes compared to archaeophytes (76.7% vs 39.4%), while naturalized but non-invasive taxa follow the reversed pattern (18.8% vs 57.4). However, these two groups do not significantly differ in the proportion of invasive taxa. Of introduced neophytes, 250 taxa (22.6%) are considered vanished, i.e. no longer present in the flora, while 23.3% became naturalized, and 4.5% invasive. Analysis of the dates of the first record, known for 771 neophytes, indicates that alien taxa in the flora have been increasing at a steady pace without any distinct deceleration trend; by extrapolating this data to all 1104 neophytes recorded it is predicted that the projected number would reach 1264 in 2050. Deliberate introduction was involved in 747 cases (51.4%), the remaining 48.6% of taxa are assumed to have arrived by unintentional pathways. Archaeophytes are more abundant in landscapes, occupy on average a wider range of habitat types than neophytes, but reach a lower cover in plant communities. The alien flora is further analysed with respect to representation of genera and families, origin and life history.