The condensed tannins (proanthocyanidins) in seagrasses

In a survey of 29 species in the 12 seagrass genera, those in the Potamogetonaceae that characteristically have tannin cells in the leaves (Posidonioideae: Posidonia; Cymodoceoideae: Halodule, Syringodium, Cymodocea, Thalassodendron, Amphibolis) contained compounds with the R_f values and color reactions typical of condensed tannins. Species in the Potamogetonaceae that are not characterized by tannin cells in the leaves (Zosteroideae: Zostera, Phyllospadix, Heterozostera) contained compounds with the R_f values associated with condensed tannins but without the typical staining reactions. Two of the three genera in the Hydrocharitaceae (Enhalus, Thalassia) are characterized by tannin cells in the leaves and contain compounds with the R_f values of condensed tannins but only some of the typical staining reactions. The third genus, Halophila, lacks tannin cells in the leaves and contains compounds with the R_f values of condensed tannins without the typical staining reactions. The role of condensed tannins as feeding deterrents because of their protein-binding properties has been well established for many land plants, but their role in seagrass biology has not been assessed fully.