Sand-trapping mechanism in psammophyte Ifloga spicata (Asteraceae)

Sands are a harsh habitat with limited water and nutrients, and danger of burial or mechanical injury by moving particles. Sand entrapping plants (psammophytes) actively fix sand on their surfaces, which presumably offers adaptive benefits, such as mechanical protection and camouflage. This short article deals with the structural-functional aspects of sand-trapping in the annual psammophyte Ifloga spicata (Asteraceae). Ifloga spicata outer surfaces are entirely covered with a dense coating of particles, mainly sand and dust. The leaves are needle-shaped and curled with the adaxial surface hidden inside. The entire outer epidermis is secretory, comprised of large cells with thick pectinaceous cell walls and upper cell wall junctions with numerous wall creases. Ruthenium red staining of fresh hand sections of the leaf demonstrated that the outer epidermal cells produce a pectinaceous substance, which upon wetting ruptures outside the cell, resembling pectin "rays" in the Arabidopsis seed coat. TEM imaging showed vesicles arriving at the plasmalemma, fusing with it and the secretory product accumulated in periplasmic spaces inside the cell wall. Ifloga spicata and other sand entrapping plants live in nutrient poor habitats. Foliar particle capture could have an additional benefit of phosphorus accumulation from leaf deposited dust particles, as known in several Mediterranean origin plants.