Global Survey of Ex situ Zelkova Collections
In 2010, a worldwide survey was carried out to gauge the status of Zelkova species in living ex situ collections, including a presence-absence analysis, an assessment of the extent and average size of collections, as well as of plant provenance and genetic representativeness.
By and large, the majority of botanic institutions with Zelkova collections are not found in locations of their origin, but in central and northern Europe and North America, in countries with a long-standing horticultural tradition. Of the 275 Zelkova records (collections) gathererd from 146 institutions in 27 countries, almost 50% of all Zelkova ex situ collections are in the United States, United Kingdom and Germany. Other countries with significant collections include China, France, Belgium and Australia. Except for the East Asiatic species Z. sinica, serrata and schneideriana that are worldwide best represented in some 25 Chinese collections, the Mediterranean Z. sicula and Z. abelicea as well as the Transcaucasian Z. carpinifolia species are found to a very limited degree in the countries of the species’ natural distribution. Zelkova species with the widest distributional range (Z. serrata and Z. carpinifolia) are also the most common ones represented in ex situ collections, whereas, as can be expected, the most threatened species (Z. sicula, Z. abelicea and Z. sinica) are least in cultivation.
Worldwide distribution of Zelkova spp. collections and extent of collections in-country
Generally, collections are small, in 90% of the records they either hold one individual or two to 10 trees at most. In addition, the majority of ex situ collections is not well documented. Not only is the origin of the plant material unknown, but often also their taxonomic status and/or cultivation history in the given institution. These collections are therefore inappropriate for scientific study and unsuitable for practical conservation, especially for restoration programmes.
A mere 20% of the plants grown in ex situ collections is of known wild provenance. While ex situ collections of Z. carpinifolia represent to some extent the in situ variability of its two distinct, phylogeographic western and eastern lineages (some 15 haplotypes identified to date) with 10 botanic gardens hosting trees from both groups (representing 11 haplotypes), the complex genetic diversity of Z. abelicea is not reflected in collections with only two out of at least 36 haplotypes found in botanic gardens. As far as Z. sicula is concerned, all five existing collections are based on plant material gathered from the population discovered 1991.