Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: Most modern plants, like the skunk cabbage, produce flowers. However, flowers evolved relatively late in the history of plants. The earliest plants not only lacked flowers. They also lacked leaves, roots, and stems. They probably resembled the alga in Figure below . Answer: plants
The earliest types of what lacked flowers, leaves, roots and stems?