Species of the genus Hypoxis L. are used for herbal remedies throughout the world. In Asia use is made of H. aurea (), while in the West Indies H. decumbens and H. scuronera are collected for curing tumors of the testicles. Utilization of this genus is, however, most frequent on the African continent, where species such as H. rooperi are extensively employed in folk medicine. The merit of these folk medicines has been recognized by the scientific, medical, and commercial communities. This has resulted in attempts to isolate the medicinally active agents, to determine their range of application, to propagate the plants, and to produce the required chemicals by suspension culture.
Distribution and Morphology of Hypoxis L.
The genus Hypoxis L., together with the genera Curculigo Gaertn., Empodium Salisb., Molinera Colla., Pauridia Harv., Rhodohypoxis Nel and Spiloxene Salisb. belongs to the family Hypoxidaceae, which is widely distributed throughout the world with the exception of Canada and Europe. The genus Hypoxis shows a similar distribution but is concentrated in the tropics and subtropics. Although present in the Americas (16 species) and Asia-Australasia (7 species), the largest number of species are found in Africa (96 species). Of these, 46 are found in tropical Africa and 50 in southern Africa, where they occur largely in the southeastern part of the continent as perennial grassland species. In this latter region the plants can occupy a variety of habitats, from mountainous to coastal areas and from dry grasslands to damp ravines. H. rooperi, which is the plant most extensively used and studied, follows this pattern. It is most common in grasslands where it can be found in almost pure stands.
Members of Hypoxis are perennial herbs and geophytes possessing some form of rootstock, usually a corm, which enables them to survive harsh winters, drought, and fire. The corm, in the case of H. rooperi, is a globose to oblong structure, with a diameter of 0.5 to 11 cm, from the apical region of which arises the tristichously arranged strap shaped, pubescent leaves. Numerous fleshy contractile roots emerge from the bottom half of the corm, which internally is bright yellow and mucilagenous. Yellow flowers are produced at the end of long peduncles from September to February. During this time abundant small black seeds are proliferated. For approximately 1 month in winter the aerial parts of the plant die back, but reappear in early spring.
In Africa many tribes use members of the genus Hypoxis as herbal medicine and as food during famines. The rootstock is used predominantly as a source of potions for a large array of ailments, of which diseases of the urogenital system are most prevalent. Aqueous preparations of the corms from various Hypoxis species are used as a panacea for prostate hypertrophy. In fact, in South Africa sun-dried material of Hypoxis corms is marketed under the trade name Prostamin for the preparation of such aqueous potions. A number of patents claim that Hypoxis corm extracts exhibit antibody and anti-inflammatory properties. Some extracts are also reputed to relieve arthritic conditions. Dermatological diseases are included in the list of cures.
The Hypoxidaceae is closely related to the Amaryllidaceae and Liliaceae. Some members of the latter two families accumulate alkaloids and steroid spiroketal glycosides which are toxic. No evidence for the presence of such compounds has been reported for a wide range of Hypoxis species, the only exception being the occurrence in the corms of H. latifolia of haemanthine, an alkaloid which is reputed to be very poisonous. To date, the steroid spiroketal glycosides have not been detected in the genus Hypoxis. There are, however, a number of reports which have identified the presence of sterols and their glycosides in Hypoxis species particularly in H. rooperi. Walford (1979) and Pegel (1980) maintained that no toxicity was associated with the steroid fraction of H. rooperi corms. These extracts displayed neither carcinogenic nor teratogenic properties when tested on rats. In fact, extracts from members of the Hypoxidaceae have been shown to possess anti-cancer properties when used in the mouse lymphocytic leukemia (P-388) test.
Other compounds conclusively identified in H. rooperi corm extracts include the following fatty acids; palmitic, septadeconoic, stearic, sepdecatrienoic, octadecenoic and octadecadienoic acids, and the carbohydrates glucose, fructose, sucrose and starch.
As far as the presence of phenolic compounds is concerned, reports are inconclusive except for a few recent publications which refer to specific phenolic compounds. Wall et al. (1954) detected phenols in H. rooperi but these were not specified. Skryzypczakowa (1970) found flavonoids, anthocyanidins, caffeic acid, p-coumaric acid, and ferulic acid in a number of unnamed Hypoxis species.
While the sterols and their derivatives show definite medicinal activity, hypoxoside is now thought to be responsible for some of the many medicinal properties displayed by the genus Hypoxis, particularly the curing of urinary infections, prostatic hypertrophy and internal cancer. It is of interest that Van Staden et al. (1986) have discovered that hypoxoside will inhibit kinetin-induced growth of soybean callus. This property was a function of time and its dissipation could be correlated with an accumulation of the phenolic in the cell vacuoles. Currently it is not known how cell division is inhibited. The hypoxoside displayed no toxic effects on the callus. At present, hypoxoside is being tested extensively to establish its medicinal properties. To date all evidence indicates that it is nontoxic and has neither fetotoxic nor teratogenic effects in mice. Most attention is focused on H. rooperi as a source of hypoxoside and sterols because it is abundant and produces a large corm.
Conventional Propagation of H. rooperi
Currently, H. rooperi is not cultivated and the active agents are extracted from plants collected from the wild. Serious problems can be anticipated as a result of this exploitation because the plants do not readily propagate vegetatively. In addition, the numerous apparently healthy seeds produced in summer do not germinate easily. The reason for seed dormancy is currently not known. Few seedlings are observed in nature and it has been suggested that the seeds may require an after-ripening period, as is the case with the closely related genera Forbesia, Pauridia, and Ianthe (). It is thus obvious that for a successful cultivation program, seed dormancy will have to be investigated and a means of overcoming it established. Even if successful germination is achieved, it is debatable whether propagation by this means is desirable because H. rooperi has a large and variable chromosome number (2n = 76, 96, and 114). While this large chromosome number could be useful in breeding programs, it is of limited value because the plants are thought to be apomictic and vary greatly with respect to pollen tube formation. This seems to be particularly true for H. rooperi (). Conventional means of propagating H. rooperi are therefore fraught with problems which are not easy to solve.
Selections from the book: “Medicinal and Aromatic Plants I”, 1988.