Ultrasculpture of achene surface in Polygonum section Polygonum (Polygonaceae) in Russia

Abstract

Based on SEM examination of 47 specimens and 33 species from Russia and Europe, this is a survey of achene surface ultrasculpture in 6 subsections of annual species of Polygonum. Early and late achenes detected in most species possess sound distinctions in achene shape, size, color and exocarp structure. Late achenes with early and fast seed germination preserve exocarp structure typical for premature achenes of both types: thin colorless walls and vast cavities, thin cuticle and insignificant wax deposits. Early achenes destined for long‐term preservation in soil are thickwalled and covered with thick and smooth cuticles and wax layers. The structure of achene surfaces changes substantially during maturing, especially in early achenes: coarse or foveo‐rugulate background becomes minutely rough, foveosmooth or minutely reticulate. Verrucae are not obligatory ornaments. Depending on their location and arrangement of exocarp cells the surface is evenly verrucate (subsect. Paatula Tzvel.), linear‐verrucate (subsect. Salsuginea Tzvel.) or striate‐verrucate (subsect. Humifusa Tzvel., most species in subsect. Polygonum). Smooth and glossy achenes are more common in permanently wet environments (subsect. Maritima Tzvel., Arenaria Tzvel., P. arenastrum and P. calcatum from subsect. Polygonum). In places with fluctuating availability of water the achenes have heavier sculpturing and thicker cutin and wax coverings. A broad range of surface sculptures in some species and their similarity across taxonomically distant taxa decrease the value of the characters for taxa identification.