Spinescence (including spines, thorns, and prickles) plays an important role in defense from herbivores. To examine whether spinescence evolved at random or differently in various life forms, plant organs, and aquatic taxa at the level of families, we analyzed the characteristics of wild spinescent aquatic plant species in the Yangtze Delta, East China. There were 92 such species, belonging to 33 genera and 21 families out of 203 wild aquatic vascular macrophyte species. Reproductive structures (including flowers, seeds, fruits and appendages) were well defended in the majority of aquatic plants compared with vegetative organs, especially for emerged macrophytes, probably resulting from the selective pressure from herbivores. Overall, most of the aquatic plants (67 species, 62.0% of the total number of species) had spiny reproductive structures while the others (41 species, 38.0% of the total number of species) had spiny vegetative organs, mostly in leaves, and only a few had thorny or prickly stems. In terms of spinescent aquatic species, there were significant differences among various life forms. Emerged macrophytes had 63 species, accounting for 58.3% of the whole; furthermore, the majority of such species (i.e. 42) were spinescent in reproductive organs. In contrast, the number of spiny floating and submerged plant species was eight and 37, respectively. It is noted that some families had more spiny species than others, especially the Cyperaceae and Najadaceae, which mainly defended their reproductive organs. Therefore, like terrestrial flora, aquatic plants also evolved spinescence as a defense against herbivores.

In: Israel Journal of Plant Sciences