Heterophylly in Ranunculus flabellaris: The Effect of Abscisic Acid on Leaf Anatomy

Ranunculus flabellaris Raf., the yellow water crowfoot, exhibits striking heterophylly between submerged and terrestrial leaves. Leaves produced under water are highly divided with numerous narrow lobes and deep sinuses, whereas terrestrial leaves have few broad lobes and shallow sinuses. When plants are submerged in a 25 μM solution of ABA, the typical transition from terrestrial to submerged leaves is completely suppressed and, instead, terrestrial-like leaves are produced. Image analysis techniques show that, in addition to this modification of leaf morphology, leaves produced under ABA treatment possess surface and internal features characteristic of terrestrial leaf anatomy. This study provides evidence that the environmental factors that influence the morphological and anatomical expression of heterophylly may act through endogenous ABA.