Manihot grahamii Hook. (S Am.) – An exceptional and ephemeral alien. A single individual was observed on worked-up soil in a road verge in Leuven in 2017, without obvious vector of introduction. Nearby another unusual garden ornamental was found, Alonsoa intermedia.
Manihot grahamii was recently reported for the first time in the wild in Europe: it is a naturalized escape from cultivation in the Rome area in Italy (Iberite & Iamonico 2015). A second species of the genus, M. esculenta Crantz, was also recently reported from Italy (Stinca & al. 2014).
This is the most cold-tolerant Manihot species. Above-ground stems survive light frosts and even if severe cold kills the aerial shoot system, new stems can regenerate from underground parts. In North America it survives well and self-sows in garden settings as far north as Virginia (Hayden 2016).
Selected literature
Hayden W.J. (2016) Manihot. In: Flora North America Editorial Committee (eds.), Flora of North America North of Mexico. Vol 12. New York and Oxford: 192-196. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=119615]
Iberite M. & Iamonico D. (2015) Manihot grahamii Hook. (Euphorbiaceae), a new alien species for the Eurasian area with nomenclatural, taxonomical, morphological and ecological notes. Acta Botanica Croatica 74(1): 143-150. [available online at: https://www.degruyter.com/downloadpdf/j/botcro.2015.74.issue-1/botcro-20...
Stinca A., D’Auria G. & Motti R. (2014) Manihot esculenta (Euphorbiaceae), a new alien species in Italy. Hacquetia 13: 355–357. [available online at: https://ojs.zrc-sazu.si/hacquetia/article/viewFile/2820/2583]