Yucca is a taxonomically difficult genus with ca. 35-47 species, all originally native in the United States, Mexico and Central America (Hess & Robbins 2002, Mabberley 2008). Species delimitation in Yucca is controversial and several aggregates are still insufficiently understood, including those treated in this account (i.e., series Gloriosae and Filamentosae). The genus is very popular in cultivation (e.g. Cullen 1986) and has been introduced as an ornamental in most temperate regions of the world.
Species of Yucca are popular garden plants in Belgium as well and they are regularly found where garden waste has been discarded. As such they usually soon disappeared after their introduction. In more recent times, however, although still rare, Yucca species are increasingly recorded as being established in favorable habitats, for instance in coastal dunes and on open sandy soils in the Kempen. In the absence of Yucca pollinator moths (family Prodoxidae) in Europe, sexual reproduction is impossible (see also Le Gall 2014) but self-sustaining populations are locally found as a result of strong clonal growth. These young populations were very reluctant to flower and, as a result, their identification long remained more or less tentative. In recent years, however, it has been possible to confidently identify at least part of the taxa currently found in the wild in Belgium.
In the past decades various species of Yucca have become spectacular but undesirable invaders in coastal dunes in parts of southern Europe (e.g. in France and Italy), possibly as a result of global warming. Their local naturalization in climatologically favorable areas in Belgium (e.g. coastal dunes, Kempen) is very likely. Identical records (of Yucca spec.) recently became available from the Netherlands as well (Holverda & al. 2009).
1 Leaf-margins with conspicuous splitted off filiferous threads. Plant acaulescent, with stem at most 30 cm tall. Fruit fleshy, dehiscent and erect === Yucca flaccida
Leaf-margins entire, without filiferous threads. Plant caulescent, developing at maturity a distinct stem up to 5 m tall (but much less out of doors in western Europe). Fruit dry, indehiscent and pendent or erect === Y. gloriosa
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