Most plants share the same, or similar basic cellular makeup, although there are many variations to how the cells form into tissues, and these depend greatly on the requirements of the plant that have evolved over many years.
The basic requirements of plants remain broadly similar in that they have organs for collecting water, organs for collecting oxygen and carbon dioxide, and methods of combining these ingredients to create food for the plant. Some have evolved different methods of doing this according to the environment in which the plant has developed. This is either as a result of needing to survive in either dry or waterlogged conditions, or the need to develop protective measures such as spikes instead of leaves, thus requiring other parts of the plant to take on the function of photosynthesis.
Such development and evolution of plants is an ongoing process, and plants continue to adapt to ever changing conditions.