What type of muscle tissue lacks striations and is under involuntary control?

Smooth muscle tissue is characterized by the absence of striations, which distinguishes it from skeletal and cardiac muscle. It is composed of spindle-shaped cells that are not aligned in a regular pattern, giving it a smooth appearance under the microscope. This type of muscle is responsible for involuntary movements within various systems of the body, such as the digestive tract, blood vessels, and the respiratory system.

Involuntary control means that the contractions of smooth muscle occur automatically, without conscious effort, unlike skeletal muscle, which is under voluntary control and enables movement of the skeleton. Cardiac muscle, while striated and involuntary, is specific to the heart. Circular muscle typically refers to a structural arrangement found in smooth muscle but is not a standalone type of muscle tissue. Hence, the defining features of smooth muscle align perfectly with the question, making it the correct answer.