Ziziphus Mill.

Although only Ziziphus jujube Mill. extends the range of this genus into warm temperate regions and is likely be the only species at all familiar to northern gardeners, it represents in fact a large and largely tropical group; Plants of the World Online (Royal Botanic Gardens, Kew 2024) recognises 68 Ziziphus species. Among the taxa which receive no additional treatment in this account, Z. lotus (L.) Lam. is a common shrub in hotter and drier parts of the Mediterranean; like Z. jujube it carries edible (if rather small and sour) fruit and, along with Celtis australis and Diospyros lotus, it is a candidate for the Homeric ‘lotus’. This fruit, in common with that of Z. jujube, is also of particular interest for its pharmaceutical properties, and is traditionally used to treat diabetes, digestive problems, urinary tract problems, infectious diseases, cardiovascular disorders, neurological diseases, and dermal problems (Bencheikh et al. 2013). The plant is not at all well adapted to survive in cooler, wetter parts of Europe, although it can occasionally germinate from discarded stones and persist for a few years (Manual of the Alien Plants of Belgium 2024). Z. spina-christi (L.) Desf. has long been grown in warm Mediterranean regions but its native distribution lies south of the Sahara and eastwards to the deserts of Pakistan; along with Paliurus spina-christi it is traditionally believed to the plant from which Christ’s crown of thorns was made. Z. mauritiana, the Ber or Indian Jujube, is an important fruit tree in tropical and subtropical climates. Z. nummularis (Burm.f.) Wight & Arn., a desert species whose range extends eastwards from the Sinai peninsula to western India, has been cultivated at the New York Botanical Garden (Royal Botanic Garden Edinburgh 2024).

All of the New World taxa that used to be placed in Ziziphus have recently been transferred to the allied genera Condaliopsis and Pseudoziziphus (Royal Botanic Gardens, Kew 2024). Four of these species enjoy natural ranges extending northwards into the United States, while a fifth is endemic to Florida. Condaliopsis obtusifolia (Hook. ex Torr. & A.Gray) Suess., the Lotebush, Graythorn, Gumdrop Tree or Texas Buckthorn, is a shrub with narrow grey-green leaves from arid parts of Arizona, New Mexico, Oklahoma and Texas. With a more westerly and disjunct distribution in Arizona, California, Nevada and Utah, C. divaricata (A.Nelson) G.L.Nesom shares many of these vernacular names and is cultivated, from various provenances, at the Denver Botanic Gardens, Colorado (Royal Botanic Garden Edinburgh 2024). Within the United States, C. rigida (Wiggins) Wiggins is recorded only from New Mexico. Pseudoziziphus parryi (Torr.) Hauenschild, the Abrojo or Crucillo, occurs in chaparral habits in the far south of California. P. celata (Judd & D.W.Hall) Hauenschild, the Florida Jujube, with even tinier leaves, is endemic to sandy places in the Lake Wales Ridge in Highlands and Polk Counties, Florida, where it has been assessed as Critically Endangered (Nesom 2016; Royal Botanic Gardens, Kew 2024; IUCN 2024). None of these species are likely to be at all easy to grow out-of-doors in the more temperate parts of North America, or in northern Europe.

The characteristic paired spines of Ziziphus, which are modified stipules, are a feature shared with Paliurus; the leaves of both genera also typically show three strong veins from the leaf-base. Another unusual feature common to many species of Ziziphus is that most of the year’s side-shoots are shed, along with the leaves, in winter or in the dry season. This characteristic can also be seen in Taxodium and Metasequoia – but does not in this case of course imply a closely shared evolutionary lineage.