Studies on the foliage of Myricaria germanica (Tamaricaceae) and their evolutionary and ecological implications

Abstract

Key message Ancestral halophytic traits such as salt glands and leaf deciduousness have facilitated the adaptation of Myricaria germanica to non-saline calcium-rich soils. Abstract Myricaria germanica is a scale-leaved, deciduous shrub from the Tamaricaceae, a salt gland family of halophytes, xerophytes and rheophytes usually from xeric, saline areas. Atypically, the genus Myricaria is usually from mesic, non-saline areas. In this study, we describe the shoot morphology and anatomy of seedlings and adult plants of Myricaria germanica in order to explore its adaptation to the environment. It is a species of montane to subalpine-flooded riverine areas on non-saline limestone and dolomite soils. The adult leaves show strong leaf reduction but no other significant xeromorphic or scleromorphic features. While the salt glands of most Tamaricaceae secrete NaCl, our SEM EDS investigations show that Myricaria germanica secretes large amounts of Ca and Mg, probably as CaSO4 and as Mg-containing CaCO3, rather than NaCl. This suggests that the evolution of salt glands in a halophytic ancestor may have been an enabling trait that facilitated the adaptation of Myricaria germanica to non-saline Ca-rich soils. Because leaf deciduousness can also be an adaptation for reduction of plant NaCl content, the same may apply to this Myricaria germanica trait. Similarly, leaf reduction can evolve as a response to osmotic stress in saline areas. Its persistence in Myricaria germanica may no longer have any adaptational significance. Our work highlights the dichotomy of the stress-tolerant family Tamaricaceae into two types of stressful habitats, one lowland (e.g. Tamarix) and one montane to alpine (Myricaria). Similar range fragmentation is known in Mediterranean taxa like Armeria and Astragalus.