Final answer:
The representation of the initial height of the cactus when Lauren planted it can be found at the starting point or y-intercept of the graph, showing the height at the beginning of the plotted time period.
Step-by-step explanation:
The feature of the graph that represents how tall the cactus was when Lauren planted it is the initial height of the cactus on the graph. This is usually indicated by the starting point or the y-intercept of the graph if we are plotting the growth of the cactus over time with the height on the y-axis and time on the x-axis. The initial value where the graph crosses the y-axis corresponds to the height of the cactus at the beginning of the time period represented.