The freshwater angiosperm Hippuris vulgaris L., Mare's-tail, exhibits distinct morphological and anatomical differences between leaves produced on submerged and aerial shoots.
… Heterophyllic development usually occurs following submergence or emergence of the shoot apex. The hormonal basis for aerial leaf development was examined by culturing submerged shoots in the presence of 0.1 -μM abscisic acid (ABA) in half-strength Murashige and Skoog medium supplemented with either 3% (w/v) sucrose or bubbled with 1% (v/v) carbon dioxide in air for 20 days. Submerged plants cultured in the presence of 0.1-μM ABA flowered and produced leaves with all the aerial leaf characteristics, including increased cuticulization, presence of stomata, reduced epidermal cell lengths, branched vasculature and differentiated mesophyll. Submerged shoots grown in media of lower water potential (−1.1 MPa) similarly developed aerial-type leaves. A regulatory role for endogenous ABA content, possibly mediated by emergence-induced water stress, in the control of aerial leaf development in Hippuris is suggested. (MORE) 
