xerotphytic plants has special charcterstic to perform photosynthesis . to perform photosynthesis we need CO2,H2O,sunlight chlorophyll. all plants get CO2 from atmosphere, sun light from sun, chlorophyll already present in plant,water absorbed from roots. xerotphytic plants also get all of these sufficiently except water because they grow in water scarcity areas . so they store water in stems and trunks and they don t allow so much transpiration. thus they perform photosynthesis
Xerophytes have sunken stomata, or smetimes stomata may be absent....they have thick waxy cuticle to reduce the rate of transpiration...... so all these adaptations helps in conserving water.....hence they can perform photosynthesis even when water is less