Stem structure strongly influences the drought response across a diverse group of temperate and tropical tree species. The stem of Salvadora persica (miswak), used as a chewing stick in the Islamic world, has a number of distinctive xeromorphic characteristics adapting it to arid or semi-arid conditions. The thick periderm is interrupted at points around the stem by transversely oriented lenticels to moderate exchange of vital gases. On the stem surface are 3-dimensional epicuticular crystals of various shape and size, present to protect against UV exposure, insects and pathogens. The secondary xylem contains groups of xylem fibers which consist of thickwalled narrow cells. Vessels are axially oriented without branching for interconnection. The xylem is also composed of parenchyma cells, which are characterized as ray parenchyma and wood parenchyma. The woodparenchyma become crushed in the middle, forming a chamber which is later filled with amorphous inclusions or rhombohedral crystals. SEM-EDX analysis revealed sulphur in wood parenchyma cells, likely a defense against pathogenic microorganisms. Apart from its adaptive value, the sophisticated stem anatomy of Salvadora persica, in combination with its chemistry, makes it an effective tool for oral hygiene.
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