macrocystis pyrifera / giant kelp
The macrocystis pyrifera, also known as giant kelp, is a fast-growing algae. It is known for getting very big in scale in a short time.
Sensing
This plant can easily be perceived through a glass aquarium or something similar. Due to its size, macrocystis pyrifera can be seen without further tools.
Communication
As the giant kelp is an algae, there is almost no way to communicate with it. One could only change the environment of the plant and wait for a change in its growing behaviour. Besides that, there is a measurable difference in "acoustic behaviour" based on environmental circumstances [1]. In macroscale, they also seem to react to wave exposure [2].
Space
Macrocystis pyrifera thrives in cool water with a temperature below 21°C. The ground should be rocky and build possible "anchors" for the plant. It can build large kelp forests due to its rapid growth (up to 0.3m per day).