Root hair anatomy and morphology in Posidonia oceanica (L.) Delile and substratum typology: First observations of a spiral form

The morpho-anatomical root hair features of P. oceanica ramets collected in meadows settled on different substrata (sand, matte and rock) were analysed. On each substratum, nine plagiothropic rhizomes each one composed by 3-6 interconnected short shoots were collected between April and May 2016 at 10 m of depth. On sand and on rock, the adventitious roots showed two distinct tubular and spiral-shaped hairs, clustered in yellowish-gray gelatinous pads. Tubular root hair tips were dactiliform and generally attached to grains of rock fragments. Moreover, a sub-circular swelling zone occurred. On matte, root hairs did not form gelatinous pads, were very short and had a simple distal portion. The root hair anatomy and morphology described here provides new information on the P. oceanica root system that can express a remarkable root hair polymorphism.