1. Key Difference 1: Execution Flow - The execution flow in Cucumber is driven by scenarios written in Gherkin format, representing the behavior of the system. On the other hand, JBehave uses stories written in plain text and uses a stepwise execution approach.
2. Key Difference 2: Language Support - Cucumber has extensive language support, providing bindings for multiple programming languages like Java, Ruby, and JavaScript. JBehave, on the other hand, focuses primarily on the Java programming language.
3. Key Difference 3: Reporting - Cucumber provides rich and detailed reporting by default, allowing users to generate reports in various formats like HTML and JSON. JBehave, although it provides some default reporting capabilities, lacks the same level of customization and flexibility.
4. Key Difference 4: Integration - Cucumber offers seamless integration with other testing frameworks and tools like Selenium and JUnit. JBehave, while it can be integrated with external tools, does not provide the same level of integration options.
5. Key Difference 5: Scenario Reusability - Cucumber promotes scenario reusability through the use of step definitions. Steps can be shared across multiple scenarios, reducing duplication and improving maintainability. In JBehave, the focus is more on the sequential execution of stories, making scenario reusability less straightforward.
6. Key Difference 6: Community and Popularity - Cucumber has a larger and more active community, with extensive documentation, tutorials, and support. JBehave, while it also has a community, is not as widely adopted and may have fewer resources available for assistance and learning.

In summary, Cucumber and JBehave differ in execution flow, language support, reporting capabilities, integration options, scenario reusability, and community popularity.