Final answer:
The tundra has the least amount of vegetation present due to its harsh conditions, such as extremely low temperatures, poor nutrients, and short growing seasons.
Step-by-step explanation:
The ecosystem that typically has the least amount of vegetation present is the tundra. The tundra is characterized by extremely low temperatures, little precipitation, poor nutrients, and short growing seasons, which significantly limits the types of vegetation that can thrive. In contrast, deserts, while also having sparse vegetation, can still support a variety of plant life such as saguaro cacti, especially in regions like the Sonoran Desert. On the other hand, rainforests and grasslands have a much greater abundance and diversity of plant life.