A morpho-anatomical characterisation of Myrothamnus moschatus (Myrothamnaceae) under the aspect of desiccation tolerance

Morpho-anatomical traits of the rarely studied dicotyledonous desiccation-tolerant shrub Myrothamnus moschatus were examined and compared for the first time to Myrothamnus flabellifolius under the aspect of desiccation tolerance. Both species almost exclusively occur on rock outcrops and differ mainly in their geographic range and leaf morphology (fan-shaped in M.similar to flabellifolius, lanceolate in M.similar to moschatus) but have a very similar leaf and wood anatomy, except for the lack of hydathodes in M.similar to moschatus. Both species adopt the parallel leaf venation of monocots, although this is more pronounced in M.similar to moschatus. This provides a mechanical and protective advantage over the net venation pattern of most dicots and facilitates the reversible, drought-induced, accordion-like leaf contraction. The sclerenchyma, as a stabilising tissue, is mainly confined to vascular bundles in leaves of both species. Here, mechanical support seems to be less crucial for survival in long periods of drought than other morpho-anatomical traits (e.g. parallel leaf venation).