Under watering can lead to which of the following effects?

Under watering can lead to smaller leaves because when plants do not receive sufficient water, they experience stress. This stress often results in the plant conserving resources, thus limiting growth in certain areas, including leaf development. Water is essential for plant cell expansion, and without adequate moisture, the cells cannot grow to their full potential, leading to smaller overall leaf size.

On the other hand, options that describe full, lush growth or improved photosynthesis are incorrect since these conditions generally require adequate watering. Similarly, longer flowering times may occur due to various stress factors, but under watering typically disrupts the overall health of the plant, making it less likely to thrive and produce flowers for an extended period.