Question: What is the name of one of the native species of buckthorn that is also a powerful plant-based laxative?

full_context: Document 1: List of coffee dishes: This is a list of coffee dishes, which includes foods that use coffee as a primary ingredient, and for which coffee is an essential ingredient. Coffee beverages are omitted from this list.
Document 2: Camellia sinensis: Camellia sinensis is a species of evergreen shrub or small tree whose leaves and leaf buds are used to produce tea. It is of the genus "Camellia" () of flowering plants in the family Theaceae. Common names include "tea plant", "tea shrub", and "tea tree" (not to be confused with "Melaleuca alternifolia", the source of tea tree oil, or "Leptospermum scoparium", the New Zealand teatree).
Document 3: Coffee cherry tea: Coffee cherry tea is a herbal tea made from the dried skins of dried berries (or "cherries") of the coffee plant. It is also known as "cascara", from the Spanish cáscara, meaning "husk". It is different from cascara sagrada tea, a powerful plant-based laxative.
Document 4: Purshia: Purshia (bitterbrush or cliff-rose) is a small genus of 5-8 species of flowering plants in the family Rosaceae, native to western North America, where they grow in dry climates from southeast British Columbia in Canada south throughout the western United States to northern Mexico. The classification of "Purshia" within the Rosaceae has been unclear. The genus was originally placed in the subfamily Rosoideae, but is now placed in subfamily Dryadoideae.
Document 5: Polygonum cascadense: Polygonum cascadense is a species of flowering plant in the buckwheat family known by the common name Cascade knotweed. It has been found only in the State of Oregon in the northwestern United States, in the Cascades and in the Blue Mountains.
Document 6: Hippophae rhamnoides: Hippophae rhamnoides, also known as common sea buckthorn is a species of flowering plant in the family Elaeagnaceae, native to the cold-temperate regions of Europe and Asia. It is a spiny deciduous shrub. The plant is used in the food and cosmetic industry, in traditional medicine, as animal fodder and for ecological purposes.
Document 7: Coffee: Coffee is a brewed drink prepared from roasted coffee beans, which are the seeds of berries from the "Coffea" plant. The genus Coffea is native to tropical Africa (specifically having its origin in Ethiopia and Sudan) and Madagascar, the Comoros, Mauritius, and Réunion in the Indian Ocean. The plant was exported from Africa to countries around the world and coffee plants are now cultivated in over 70 countries, primarily in the equatorial regions of the Americas, Southeast Asia, India, and Africa. The two most commonly grown are the highly regarded arabica, and the less sophisticated but stronger and more hardy robusta. Once ripe, coffee berries are picked, processed, and dried. Dried coffee seeds (referred to as beans) are roasted to varying degrees, depending on the desired flavor. Roasted beans are ground and brewed with near-boiling water to produce coffee as a beverage.
Document 8: Berberis aristata: Berberis aristata, also known as Indian barberry, "chutro" or tree turmeric, is a shrub belonging to the family Berberidaceae and the genus "Berberis". The genus comprises approximately 450-500 species of deciduous evergreen shrubs and is found in the temperate and sub-tropical regions of Asia, Europe, and America. "B. aristata" is native to the Himalayas in India and in Nepal. It is also naturally found in the wet zone of Sri Lanka.
Document 9: Rhamnus purshiana: Rhamnus purshiana (cascara buckthorn, cascara, bearberry, and in the Chinook Jargon, chittem and chitticum; syn. "Frangula purshiana", "Rhamnus purshianus") is a species of buckthorn native to western North America from southern British Columbia south to central California, and eastward to northwestern Montana.
Document 10: Rhamnus davurica: Rhamnus davurica is a species of flowering plant in the buckthorn family known by the common name Dahurian buckthorn. It is native to China, North Korea, Mongolia, eastern Siberia, and Japan. It is present in North America as an introduced species.
Document 11: Coffea: Coffea is a genus of flowering plants whose seeds, called coffee beans, are used to make various coffee beverages and products. It is a member of the family Rubiaceae. They are shrubs or small trees native to tropical and southern Africa and tropical Asia. Coffee ranks as one of the world's most valuable and widely traded commodity crops and is an important export product of several countries, including those in Central and South America, the Caribbean and Africa.
Document 12: Kuding: Kuding or ku ding (; pronounced ) is a particularly bitter-tasting Chinese infusion, which due to their similarities in appearance is derived from several plant species. Two most common plants used to make kuding, being the wax tree species "Ligustrum robustum" and the holly species "Ilex kaushue" (synonyms: "Ilex kudingcha") plant, the former being more commonly grown in Sichuan and Japan while the latter is most commonly grown and used in the rest of China. This type of tea may be caffeinated if from the "Ilex" genus, but is caffeine-free if from the Ligustrum genus.
Document 13: Cherry RC: Cherry R.C. is a cherry-flavored version of the RC Cola soft drink that competes with Coca-Cola Cherry and Pepsi Wild Cherry. It was introduced in 1985. This was the first cherry cola beverage to actually contain "Real Cherry Syrup." The beverage is a product of Dr Pepper Snapple Group.
Document 14: Cotoneaster dammeri: Cotoneaster dammeri, the bearberry cotoneaster, is a species of flowering plant in the genus "Cotoneaster", belonging to the Rosaceae family, native to central and southern China (Gansu, Guizhou, Hubei, Sichuan, Tibet and Yunnan) and naturalized in Europe.
Document 15: Arctostaphylos rubra: Arctostaphylos rubra is a species of flowering plant in the heath family and the genus "Arctostaphylos", the manzanitas and bearberries. Common names include red fruit bearberry, alpine bearberry, arctic bearberry, red manzanita, and ravenberry. It is native to Eurasia and northern North America from Alaska through most of Canada to Greenland. There is also one population in the contiguous United States, located in the Absaroka Mountains of Wyoming.
ground_truth: Rhamnus purshiana