Background and aim – Desert rhubarb (Rheum palaestinum Feinbr.), a rare perennial plant endemic to Jordan and southern Israel, grows in areas with very low annual rainfall. It produces large leaves, atypical for a desert plant, that are tightly attached to the ground. The leaves have a unique morphology thought to be involved in water catchment and drainage systems along the central stem. The objective of this study was to simulate the leaf morphology of the rhubarb and investigate its function as a 'condensation trap'.
Methods – A field study was conducted on seven plants growing in one location in the desert of Jordan. Three-dimensional modelling software was used to identify the foliar architecture and the vapour-trapping and drainage system employed by the plant.
Results – The complex leaf morphology protects against excessive transpiration by self-shading, significantly increasing the surface area to maximise condensation mostly on the lower surface of the leaf, and to a lesser degree on the upper surface.
Conclusions – While previous scientific research has pointed to this plant's ability to irrigate itself, it has to a large extent been misunderstood how this self-irrigation system works. The rhubarb leaf must have evolved not as water catchment and drainage system but as a 'trap' for sub-foliage moisture. This method of self-irrigation by sub-foliar condensation has not been previously recognized in plants.

3D MODELLING; DESERT RHUBARB; MOISTURE TRAP; SELF-IRRIGATION; SUB-FOLIAR CONDENSATION