Rheum palaestinum (desert rhubarb), a self-irrigating desert plant

Simcha Lev-Yadun, Gadi Katzir, and Gidi Ne'eman, all from the Department of Science Education—Biology, at the University of Haifa, Israel wrote their results in the journal Naturwissenschaften, which was published online on November 22, 2008

Special leaves with the depth furrowdrain leads the water run off to the base and roots, photo from treknature.com.

They state in their abstract, “These leaves differ markedly from the typical small leaves of most desert plants. Moreover, they have a unique 3D morphology resembling a scaled-down mountainous area with well-developed steep drainage systems, raising the question which selective agents were involved in their evolution.”

The Israeli researchers state that these large leaves collect rainwater and directs it to its root system.

They state, “We measured the seasonal course of leaf growth, examined the area of wet soil surrounding the root after actual and simulated rain, and modeled the water harvesting capacity using the plant leaf area and the weekly precipitation. We show that even in the slightest rains, water flows above the veins to the leaf’s base where it irrigates the vertical root.”

And, “A typical plant harvests more than 4,100 cm3 [cubic centimeters] of water per year, and enjoys a water regime of about 427 mm/year [millimeters per year], equivalent to the water supply in a Mediterranean climate. This is the first example of self-irrigation by large leaves in a desert plant, creating a leaf-made mini oasis."

For more information on this exciting discovery, please read the May 14, 2009 BBC News article “The plant that can water itself.”

Further research into this plant could help to provide more plant growth in arid, desert-like climates around the world

More information from springerlink.com

The rare plant Rheum palaestinum (Polygonaceae) is a perennial hemicryptophyte that grows during the rainy winter in desert mountainous areas in Israel and Jordan that receive an average annual rainfall of ca. 75 mm. It produces between one and four large round leaves that are tightly attached to the ground and form large rosettes of up to 1 m². These leaves differ markedly from the typical small leaves of most desert plants. Moreover, they have a unique 3D morphology resembling a scaled-down mountainous area with well-developed steep drainage systems, raising the question which selective agents were involved in their evolution. We propose that the large leaves collect rainwater that then infiltrates the soil surrounding the root. We measured the seasonal course of leaf growth, examined the area of wet soil surrounding the root after actual and simulated rain, and modeled the water harvesting capacity using the plant leaf area and the weekly precipitation. We show that even in the slightest rains, water flows above the veins to the leaf’s base where it irrigates the vertical root. A typical plant harvests more than 4,100 cm³ of water per year, and enjoys a water regime of about 427 mm/year, equivalent to the water supply in a Mediterranean climate. This is the first example of self-irrigation by large leaves in a desert plant, creating a leaf-made mini oasis.

flowering on desert, photo from BBC

Water shortage, caused by unpredictability of rainfall amount and timing, is the most important constraint on plant growth in arid environments worldwide. It has driven the evolution of numerous adaptations that increase water absorption, storage, efficient use, and decrease of losses (Evenari et al. 1982; Fahn and Cutler 1992). Many desert plants have dual root systems; (1) deep vertical roots with narrow xylem vessels to absorb deep soil water and (2) shallow horizontal roots with wide xylem vessels for rapid capturing of superficial and temporary water flows following light rains (Fahn 1964). The rare plant Rheum palaestinum Feinbr. (Polygonaceae) is endemic to Israel and Jordan, growing in mountainous desert areas receiving an average annual rainfall of ca. 75 mm (Feinbrun 1944; Zohary 1966). Its highly atypical large, round leaves differ markedly from the typical small leaves of most desert plants (Smith 1978). This raises the question which selective agents were involved in the evolution of these unique leaves. Our aim was to examine the adaptive role of this unique leaf morphology in the desert environment. We hypothesized that the large leaves efficiently collect rainwater from their total area, which is drained to their base, where it infiltrates the soil surrounding the root.

Source: BBC and springerlink.com