Micromorphology of the petals of the invasive weed, Oxalis pes‐caprae

Abstract

The alien, seedless Oxalis pes‐caprae has spread and colonized many areas of the Mediterranean Basin, relying on vegetative reproduction. The flowering of O. pes‐caprae is greatly accelerated by its exposure to sunlight. When the sun is shining, both sides of the petals of the funnel‐shaped, open flowers of O. pes‐caprae are exposed to the ambient conditions. In cloudy weather, only some portions of the abaxial petal surfaces of the trumpet‐shaped, closed flowers of O. pes‐caprae are exposed to the ambient conditions. The micromorphology of the petals of O. pes‐caprae was imaged by using light, scanning and atomic force microscopy. In O. pes‐caprae, conical cells are found only on the adaxial epidermis of the petals, which also consist of a narrow mesophyll with a loosely arranged parenchyma and convex cells on their abaxial epidermis. High‐resolution imaging of the petal surfaces, using atomic force microscopy, revealed that the epidermal cells are further ornamented by submicron sculptures, indicating a different roughness, density, and arrangement of the folds between the adaxial and abaxial sides of the petals. Submicron sculpturing increases the surface area of the adaxial epidermal cells of the petals and the distances between the folds are almost equal to the visible waveband. On the abaxial epidermal cells, the distances between the folds are smaller than the subwavelength spectrum. The high and the negligible values of roughness that were obtained on the adaxial and the abaxial surfaces might facilitate the capture and the reflection of light, respectively.