The answer should be xerophytes because xerophytes will have least water inside them so the rate of osmosis will be the highest in them only and so will be the osmotic pressure.
The cells contain large concentrations of solutes. These solutes attract water into the cells through a process known as osmosis, which involves water flowing in through semipermeable membranes that prevent the passage of solutes but not of water. The inflow of water swells the cells until a hydrostatic pressure is reached at which no more water will flow in. This equilibrium hydrostatic pressure is known as the osmotic pressure of the cell contents.
Osmotic pressure is thus related to salt concentration inside the cell.
Halophytes are those plants which grow in saline habitats, i.e., in salt marshes, river estuaries, saline ponds near seashore or sandy and heavy soils having excess of salts. In such habitats, the water is present in sufficient amount but due to high osmotic concentrations it is physiologically not available to normal plants. Such conditions are said to be physiologically dry.
these plants have huge accumulation of salts in cells as compared to xerophytes.
They have to absorb water from such soil with high salt concentration. To withstand at this condition, these plants activate salts in their roots. As a result, the cells of the root develop high osmotic pressure, which brings the water inside the cell by osmosis.
he highest osmotic pressure on record is 202.5 atm for marshy halophytes, Atriplex confertiola
Xerophytes are the plants which grow in dry or xeric habitats under water deficient conditions are called xerophytes. These plant need water conservation. High osmotic pressure in these plant increases turgidity of cell sap which exert force on cell wall and wilting of cell is checked. High osmotic pressure in cell sap also increases water absorption.
As Xerophytes have comparatively lesser salt concentration than halophytes, these shows relatively lower osmotic pressure than halophytes.