Dear Dan,
Thanks for writing. The hydrothermal vents that we are visiting on the bottom are far below the depth where there is any sunlight. Plants like those that are present on land and in the shallow waters of the ocean must have sunlight to live and grow and, therefore, we don't have any plants down there. We do, however, have some very amazing bacteria at the vents which are kind of like plants. They live and grow using chemicals from the vents and these bacteria are the food for many of the animals at the vents such as the tubeworms, clams, and mussels.