You are the Google search engine.
Given a query, you need to generate five useful documents for the query.

The user is trying to answer the question: "What is the name of one of the native species of buckthorn that is also a powerful plant-based laxative?" whose answer is Rhamnus purshiana.
Each document should contain about 30 words, and these documents should contain useful information.

Query: native species of buckthorn used as a laxative
Useful Output:

Doc 1: Cascara sagrada is Spanish for “sacred bark” and was used for centuries by Native Americans as a laxative. Cascara became accepted in western
Doc 2: There are three species of non-native species of buckthorn: Common  Their berries are eaten by birds, but as they are a bit of a laxative
Doc 3: For example, birds are enticed to eat the berries, but buckthorn berries have a laxative effect, robbing birds of nutrition and ensuring the
Doc 4: Alder buckthorn, a species of buckthorn native to Europe and Asia, has been used in traditional medicine for its laxative properties.
Doc 5: They also can have a severe laxative effect on some birds, sometimes even strong enough to result in death.  Buckthorn also spreads quickly and