Comparison of the wood anatomy between mangrove palms and ferns and their respective non-mangrove sister taxa. Is there convergence?

The harsh and dynamic conditions in the mangrove environment (lower water potential of salt water, high transpiration rates, periods of inundation and of drought) hinder water uptake and transport in the plants living in this habitat. Earlier studies have shown convergence in wood anatomy towards narrower, more numerous vessels for the dicotyledonous mangrove tree species if compared to their respective closest non-mangrove relatives. These vessel
characteristics contribute to a lower loss in hydraulic conductivity due to air spreading, for which the risk is high in the mangrove environment. The group of mangrove plants consists, beside dicotyledonous trees and shrubs, also of 1 palm and 3 fern species (Tomlinson 1986, Duke 2006, Spalding et al. 2010). In this study we aimed at examining whether these same characteristic wood anatomical differences exist for the monocotyledonous mangrove palm Nypa fruticans and two vascular spore plants of the mangrove genus Acrostichum, in
comparison with their non-mangrove sister species. We also added the mangrove associated palm species Phoenix paludosa to the study, expecting it to show a likewise adaptation since it is able to thrive in the back mangrove environment. Samples were collected from the wood collection of the Royal Museum for Central Africa in Tervuren (Belgium) and completed with samples from field missions where needed. The vessel characteristics were measured with image analysis software on images of transverse wood sections obtained through microtomy or micro-CT-scanning. We expected to find a clear
convergence in mangrove vessel anatomy over the entire plant phylogeny.