Frangula purshiana

Main synonym: Rhamnus purshiana. Common names: cascara (Little 1979), cascara sagrada, cascara false buckthorn (Kartesz 1999), cascara buckthorn (Elias 1980), bearberry, bearwood, bitterbark, chittam, chittem or chittim, coffeeberry, coffeetree, sacred bark, wahoo.

Usually known as Rhamnus purshiana DC., 1825 (type Clearwater River near Kamiah, Idaho). A discussion justifying use of the genus Frangula P. Miller (1754 or 1768) is in Kartesz and Gandhi (1994). Usually the group is considered as a part of Rhamnus L., sometimes being noted as the subgenus Frangula (P. Miller) Dipp. The genus Rhamnus is sometimes treated as masculine, but has been nomenclaturally conserved as feminine (Cronquist et al. 1997).

J.O. Sawyer Jr. in Hickman (1993) briefly characterizes but does not formally recognize Rhamnus purshiana var. annonifolia (Greene) Jepson, which as Rhamnus anonaefolia Greene, 1896 is treated as a synonym of the species (without discussion) by Abrams (1951) and Munz and Keck (1959).

Although Frangula purshiana is widespread and sometimes common, and is robust, it apparently also is subjected to rather intensive exploitation in considerable portions of the species' range. Veninga and Zaricor (1976) stated that there remained an abundant supply of naturally growing trees which exceeded demand. However, some populations may have been extirpated (Yocom and Brown 1971), and many are likely to be used repeatedly, so that these populations probably no longer function naturally but instead are responding to human-induced (selection) pressures. The age structure of a utilized population, and habit and dynamics of individual trees or shrubs, may be significantly different than for wild populations, with evolutionary consequences.

Southwestern Canada (British Columbia) and northwestern United States (Washington, Oregon and California, also Idaho and Montana). On the Pacific slope from southwestern British Columbia (including much of Vancouver Island) into northern California in outer Coast Ranges and the Sierra Nevada foothills (lower forest belt). Also disjunctly in the Rocky Mountains of southeastern British Columbia, far western Washington, northern (panhandle portion of) Idaho and northwestern Montana. The species' general distribution is mapped in Little (1971) and Krajina et al. (1982).

The species is fairly widespread and not infrequent in much of its range, and is sometimes common. It is considered common in southern British Columbia (south of 51?N), but rare farther north on the Queen Charlotte Islands (about 52?-54?N) (Douglas et al. 1991). Gilkey and Powell (1961) considered it common in the Pacific Northwest of Washington and Oregon. It is most common in the Puget Sound region of British Columbia and Washington, according to Collingwood and Brush (1965). The species was reported (Harshberger 1911) to be a common small understory tree on moist land in lower valleys of the dense forests to the east and southeast of Puget Sound.

In Pacific Northwest riparian forests, the species is never as abundant as Alnus rubra or Populus balsamifera subsp. trichocarpa (Kricher 1993, Habeck 1992). According to Kricher's discussion of these forests, the Populus (black cottonwood) lines river banks throughout the Pacific Northwest, and the Alnus (red alder) is also abundant along rivers and on disturbed sites from southern Alaska to southern California. Despite the wide distribution of Rhamnus, it is in the Pacific region that the genus is particularly important to animal wildlife; apparently, this is due to the relative abundance of certain species there, such as R. purshiana and three other [named] species (Martin et al. 1951).

The species is mostly distributed west of the Cascades (Habeck 1992). St. John (1963) stated that it was common along stream banks in southeastern Washington and adjacent Idaho. Harshberger (1911) reported that in the U.S. Rocky Mountains [e.g. in northern Idaho], it occurred with considerable frequency in the undergrowth of the (low-elevation) northern belt of Pinus ponderosa var. scopulorum, and that in northwestern Montana it is one of the more common shrubs in the Pinus monticola (mid-elevation) belt, which occurs on northern and eastern slopes and has its heaviest growth on level areas (including canyon bottoms) bordering the principal streams.

There is indirect evidence, obtained from reliable sources, of plant collecting from wild populations for the plant trade. Collingwood and Brush (1965) stated that the bark is collected extensively from trees in southern British Columbia, western Washington and Oregon, and northern California: "There is an annual harvest that comprises a forest industry of major importance to some rural regions." The bark is collected as strips peeled lengthwise.

Habeck (1992) reports the most effective collecting period to be mid-April until the end of August; the U.S. Forest Service (1963) stated that the peeling season usually runs from March through July. According to Sievers (1930), the collecting season opened about the end of May and closed before the rainy season set in. Veninga and Zaricor (1976) considered the collecting season to be in summer and continue until the rain ends in a region, as hot weather draws the sap from the bark into the inner tree. However, Clay-Poole (1999) reports that native North Americans considered it best to harvest the bark in late October and early November after the sap had descended down the trunk.

Collingwood and Brush (1965) stated that the demand is growing (even in competition with synthetic products), and that each year the bark gatherers must go farther back into the mountains. However, Hill (1998) reported that the chemical found in the bark can now be made synthetically, and for this reason a British Columbia law was removed that used to protect the species. In contrast, Tyler (1995) stated that some plant materials contain a large number of active principles and that purification may eliminate certain useful ones. He gave cascara (Frangula purshiana) as one of several examples where, "besides ... the isolation and purification of specific constituents is simply not necessary. It would be a waste of time and money to purify such herbal remedies ..."

Collingwood and Brush (1965) stated that in accessible areas, bark-peeling inroads have kept the average diameter down to 6 inches or less, and that such trees provide the major source of harvest. Veninga and Zaricor (1976) stated that the bark is collected properly by first cutting down the tree, so that a new tree will grow from the roots, but that if the tree is left standing and the bark stripped, it will die without resprouting. According to Collingwood and Brush (1965), a great deal of stump sprouting is precluded because the trees are not cut down after the bark has been peeled. Stumps sprout vigorously (coppice), producing 4 to 15 stems. "For this reason there is no dearth of wild bark at present."

However, Sievers (1930) reported that the tree will develop new bark if collectors in removing the bark allow enough to remain to prevent the tree from dying, and that this practice would prolong the natural supply of this valuable drug which was gradually being exhausted. Turner (1997) noted that Northwest Coast native peoples traditionally used the bark of many tree species for medicine, including cascara. Almost always, the bark pieces of the species utilized were cut in a narrow vertical strip from the sunrise side or river side of the tree. This practice was to allow the tree to continue to grow; the sunrise side was said to heal more quickly.

Michael McGuffin (in a meeting with Botany staff at TNC/ABI on Jan/10/2000) said that the American Herbal Products Association (AHPA) fairly recently surveyed its members regarding their trade in various species. He stated that their figures should be considered preliminary, and in general might include some double counting (if one company supplied another), resulting in over-reporting by as much as twice the actual usage. Thus a maximum total of 150,000 pounds of dried cascara bark per year may have been supplied in 1990, 1991 and 1992 by those AHPA members who responded, or the total for this species might be only half the above, 75,000 pounds per year (McGuffin email to TNC/ABI, Jan/27/2000). The AHPA has included this species in a more definitive planned tonnage survey for the 1999 season (AHPA letter to TNC, Jan/11/2000). He considered the cascara-sagrada trade an essentially steady rather than fluctuating market, and significantly in the market because the amount is relatively large, while noting that a few other species (particularly senna) were preferred as herbal laxatives. He was unaware of this species being cultivated (but will inquire), and thought the entire supply was probably from more or less wild sources (although likely with a well-organized/managed harvest because of company desire for stability in supply).

According to Habeck (1992), in a single [unstated] year 5 million pounds of dried cascara bark from the Pacific Northwest were processed by pharmaceutical companies. Prescott-Allen and Prescott-Allen (1986) reported (according to Norse 1990) that in Washington state, young men in interviews [year unstated] said that on a good day they could each bring in 280-300 pounds [presumably of fresh peeled bark strips -- Hill 1952, Veninga and Zaricor 1976]. The U.S. Forest Service (1963) stated that the bark's wet weight is about twice the dry weight.

The species was included in a list of the principal competing species on Pacific Northwest commercial forest land (Norse 1990), and the Vegetation Management Research Cooperative (VMRC) has selected this species to include in volume 3 (in preparation) of their autecology manuals on "problematic competitor plant species for forest vegetation managers" concerned with producing crop trees by reforestation in Washington, Oregon and northern California (VMRC 1999). Moore (1993) said that the species is especially common in heavily timbered forests.