[ < pleuro-comb. form + ancient Greek τρίβειν to rub (see tribo-comb. form) + -alsuffix1] Botanyrare designating flowers having stamens and styles so placed as to rub against the sides of visiting insects.
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1938 J. R. CarpenterEcol. Gloss 210Pleurotribal, flowers whose stamens are adapted to deposit their pollen upon the sides of insect visitors.