In a recent issue of Aquatic Botany, Tomasello et al. (2018) reported their investigation on root hair morphology in the dominant Mediterranean seagrass Posidonia oceanica (Alismatales: Posidoniaceae), and concluded that it has two types of root hairs, i.e., "tubular" and "spiral-shaped". This classification is flawed as these two "types" apparently represent just different states of the same.
To demonstrate this, we investigated root hairs of P. oceanica seedlings collected in the southern Adriatic Sea off Montenegro, at the Black Cape (Crni Rtič) close to Sutomore (N42.13595, E19.01549) using light and scanning electron microscopy following methods described in Vohník et al. (2015).