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Morphology:

Submerged foliage macrophytes have all or the great majority of their leaves underwater. As such they are highly adapted by morphological modification including especially a)loss of waxy cuticle to enable diffusion of nutrients for uptake across epidermal cells (and because loss by evaporation in not a problem underwater); b) loss of stomates (because they serve no function underwater); and c) loss of most of leaf blade (to minimize mechanical damage by water waves).

Heterophylly: Submerged are generally highly dissected, with mainly epidermis covering vascular tissue. In contrast floating and emergent leave, in contact with the atmosphere, generally retain their terrestrial ancestral shape, lacking dissection.

Control of leaf shape seems to be an interaction of abscissic acid (ABA), giberellic acid, and ethylene (Wanke 2011).  Higher concentration of ethylene in underwater leaf tissue favors the dissected leaves, while its release at the surface, in the presence of ABA, favors the undissected aerial type leaf.

Roots anchored in sediments with low to non-existend dissolved oxygen must be adapted to the severe condition.

Habitat :

Fresh to brackish water.  Most submerged leaf macrophytes are anchored to sediments, thus are restricted to shallow sites either by maximum tolerance of hydrostatic pressure, or light intensity sufficient for growth.

References:

Wanke, D.  2011.  The ABA-mediated switch between submersed and emersed life-styles in aquatic macrophytes.  Journal of Plant Research 124(4):467-475.

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