Uncovering the mechanisms of novel foliar variegation patterns caused by structures and pigments

In nature, foliar variegation has varied origins, and can be ascribed to two major mechanisms: pigment-related variegation and structural variegation caused by the optical properties of leaf structure. However, understanding of these mechanisms is still lacking, and structural mechanisms are often misinterpreted. In this study, six variegated plants native to Taiwan and two ornamental plants, with novel and unusual foliar variegation patterns, are studied to reveal their mechanisms of variegation. Two newly understood variegation patterns, the silvery white leaf surface of Begonia aptera and the varnish on basal leaflets of Oxalis corymbosa, are reported here. White to light green patches on leaf surfaces characterize the foliar variegation in the other six study species, Nervilia nipponica, O. acetosella subsp. griffithii var. formosana, Paphiopedilum concolor, Selaginella picta, Smilax bracteata subsp. verruculosa and Valeriana hsuii. All six Taiwan native plants exhibit structural variegation, five of which have air space type variegation. Surprisingly the silvery white leaf surface of B. aptera results from numerous sand-like white spots caused by intercellular space. The varnish on leaves of O. corymbosa is the epidermis type of variegation comprised of two newly identified subtypes, larger epidermal cells and thicker outer cell walls. The two ornamental plants have variegation caused by pigments: the chloroplast type from fewer chloroplasts in P. concolor and the chlorophyll type, from absence of chloroplasts in S. picta. This study extends understanding of the mechanisms of natural foliar variegation, illustrating the diversity of mechanisms by which plants may change the appearance of their leaves.