Rhus is a genus of ca. 150-200 species, distributed in warm-temperate and subtropical regions of the Old and New World. Few species are native in southern Europe but none in Belgium. Rhus is rather popular in horticulture: Tebbitt (1997) keys out 14 species for Europe but only a few are widely grown.
The Belgian representatives of Rhus have pinnately divided leaves and are the most popular in cultivation (Coombes 1994). According to van der Meijden (2005) Rhus radicans L. (syn.: Toxicodendron radicans (L.) Kuntze) (the notorious poison ivy), a climber with leaves with three leaflets, has been recorded as an escape from cultivation in the Netherlands. It was recently also reported as an escape in northeastern France (comm. J. Lambinon, 2010).
The identity of Rhus in Belgium is often critical. As a result of hybridisation specific boundaries between some popular species have become blurred. Rhus glabra and R. typhina are now more or less linked by numerous intermediates. Therefore, naming individual populations might turn out to be critical.
In general, species of Rhus are mostly relics of cultivation in Belgium (densely suckering from rhizomes). They probably never reproduce sexually (seedlings have not been reported so far).
- Young branches moderately hairy with fine, short hairs (most < 1 mm long), sometimes appearing subglabrous. Abaxial leaflet surface and central axis of the leaf glabrescent === 1. Rhus x pulvinata
- Young branches densely hairy with coarse, longer hairs (most > 1 mm long). Abaxial leaflet surface and central axis of leaf more or less persistently hairy, especially on the veins === 2. Rhus typhina
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Graebner L. (1906) Die in Deutschland winterharten Rhus. Mitt. Deutsch. Dendr. Ges. 15: 100-107.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Roloff A. & Bärtels A. (2006) Flora der Gehölze (2e Auflage). Ulmer, Stuttgart: 844 p.
Tebbitt M.C. (1997) Rhus. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 5. Cambridge University Press, Cambridge: 126-128.
Van der Meijden R. (2005) Heukels’ Flora van Nederland (23e druk). Wolters-Noordhoff, Groningen: 685 p.