Bupleurum: Biology and Cultivation
The genus Bupleurum belongs to the Umbelliferae and comprises approximately 200 species, which are distributed mainly in Eurasia. Most species are perennial herbs and some are annuals or shrubs.
The Bupleurum plants which have been utilized in medicine seem to be restricted to a few species. Hocking (1955) listed two European species, B. fruticosum and B. rotundifolium, which are called hare’s ear. The Pharmacopoeia of China (1977) describes two species, B. chinense DC. (Bei-Chaihu in Chinese) and B. scorzoneraefolium Willd. (Xiaye-Chaihu in Chinese) as original plants of a crude drug, Bupleurum root. Several other species of Bupleurum are also used medicinally in China. The Pharmacopoeia of Japan (1986) attributes the origin of the crude drug to B. falcatum L. (Mishimasaiko in Japanese) and its varieties. Crude drugs prepared from B. falcatum, B. scorzoneraefolium and B. longiradiatum Turcz. are on the Korean market (Han 1974). Concerning the taxonomy of B. falcatum and the related species or varieties, there are considerably different opinions among plant taxonomists. Ohwi (1978) regarded the two Chinese species, B. chinense and B. scorzoneraefolium, as synonyms of B. falcatum. Hiroe (1979), Hiroe and Constance (1958) and Kitamura and Murata (1978) distinguished “R falcatum” distributed in East Asia from the European species and classifiedit as a variety of the species. Thus, B. falcatum and a few related species are the major species utilized as crude drugs.
The chromosome number of Bupleurum has been studied with a few species. The known basic numbers are 4, 6, 8, 10, 13 and 14. Suzuka (1950) and Arano and Saito (1977) reported the chromosome number of B. falcatum to be 28 and 26, respectively, in somatic cells. Recently, Ezaki and Nishi (1985) have found another chromosome number (2n = 20) with the wild plants of the same species growing at the northern part of Kyushu and Yamaguchi Prefecture, Japan, as well as populations having chromosome numbers of 2n = 26 (abundant) and 2n = 28 (rare) that have been collected in Shizuoka Prefecture, Japan. The plant cultivated in Japan has 26 chromosomes in root tips, whereas European B. falcatum has 16 chromosomes (2n). Gorovoy et al. (1980) conducted karyological studies on B. scorzoneraefolium collected at the far east of the USSR, and found that the species contains chromosome races (2n =12, 16).
B. falcatum is mostly allogamous. Cross-fertilization occurs as a result of delay in pistil maturation after that of stamen by 3-4 days, although it produces seeds normally by artificial self-pollination. It is insect-pollinated. The taxonomical variation, chromosomal races, and allogamous nature of the plant would explain the cause of wide variations observed in growth habits, morphological characteristics or saponin contents, depending on the growth habitats, even within a single population.
For the production of Bupleurum root, B. chinense and B. scorzoneraefolium are cultivated and collected from natural resources in China. B. falcatum is cultivated in small quantities in Japan. All the above species are propagated by seeds in practical cultivation. The effect of temperature (Shimokawa et al. 1980 a), planting density, pinching, herbicidal treatment, growth regulator treatment, cultivation period, and pot cultivation on the growth, development or saponin content in B. falcatum were studied. Momonoki (1979) conducted extensive physiological studies on the germination of B. falcatum seeds and concluded that the irregular low germination capacity of the seeds is mostly attributable to the after-ripening period for seed maturation and to germination inhibitors in the seed coat. They proposed a stratification storage of the seeds as an effective method to improve their germination capacity. Some other reports illustrate how the germination of the seeds can be one of the main obstacles to growing this plant.
Bupleurum: Medicinal Usage
Bupleurum plants seem to be of little medicinal importance in European countries. Some examples of medicinal usage of these plants are B. fruticosum as a source of the Sardinian and Russian oils and the seeds of B. rotundifolium used in the tearing apart of a tissue.
On the contrary, several species of Bupleurum play an important role as a source of Bupleurum root (Chaihu in Chinese, Shiho in Korean, Saiko in Japanese) in eastern Asian countries including China, Korea and Japan. This drug is used as an important ingredient of various recipes in traditional medicine in these countries. Its anti-febrile, analgaesic and anti-inflammatory effects are mainly due to the saikosaponins a and d contained in it. Saikosaponins b1 and b2 are artefacts derived from saikosaponins a and d, respectively, during processing, storage, or extraction of the root. Recently, Ogihara and Amegaya (1986) have suggested that saikosaponin c, hitherto thought to be a pharmacologically inactive compound, is metabolized into active derivatives in human digestive organs. The constituents of B. falcatum was reviewed by Akahori (1980).
Medicinal and Aromatic Plants II (1989)