ABSTRACT
Aloe is a medicinal plant that has maintained its popularity over the course of time. Three distinct preparations of aloe plants are mostly used in a medicinal capacity: aloe latex (=aloe); aloe gel (=aloe vera); and, aloe whole leaf (=aloe extract). Aloe latex is used for its laxative effect; aloe gel is used topically for skin ailments, such as wound healing, psoriasis, genital herpes and internally by oral administration in diabetic and hyperlipidaemic patients and to heal gastric ulcers; and, aloe extract is potentially useful for cancer and AIDS. The use of honey may make the aloe extract therapy palatable and more efficient. Aloe preparations, especially aloe gel, have been reported to be chemically unstable and
may deteriorate over a short time period. In addition, hot water extracts may not contain adequate concentrations of active ingredients and purified fractions may be required in animal studies and clinical trials. Therefore it should be kept in mind that, in some cases, the accuracy of the listed actions may be uncertain and should be verified by further studies.
There are at least 600 known species of Aloe (Family Liliaceae) (Kawai et al., 1993), many of which have been used as botanical medicines in many countries for thousands of years (Grindlay and Reynolds, 1986; Gjerstad and Riner, 1968; Reynolds and Dweck, 1999; Swanson, 1995). Species of the genus Aloe are indigenous to Africa (A. ferox Miller, A. africana Miller, A. spicata Baker, A. platylepis Baker, A. candelabrum Berger) and Socotra (A. perryi Baker, A. forbesii Balf.fil.). Some have been introduced in Asia (A. chinensis Baker), the Barbados Islands in Central America (A. barbadensis Miller, otherwise known as A. vera [L.] Burm. or A. vulgaris Lamarck) and Europe (A. arborescens Miller). Aloe ferox, known in commerce as ‘Cape aloe,’ is easy to hybridise and cultivate in Africa. The term ‘Cape aloe,’ for accuracy, refers to the dried latex of the leaves of several species of the Aloe genus, especially A. ferox, and the hybrids and preparations made from them (Blumenthal, 1998). Aloe barbadensis, known in commerce as ‘Curacao aloe,’ was said to be native to northern Africa but was introduced into the Barbados Islands in the seventeenth century and is now cultivated in Florida, USA (Bruneton, 1999). A. chinensis, a variety of A. vera, was introduced into Curacao from China in 1817 by Anderson. The plant was cultivated in the Barbados Islands until the end of the nineteenth century. Curacao aloe is often called Barbados aloe. Other varieties are
cultivated throughout India while some grow wild on the coasts of Bombay, Gujarat, southern Arabia, Madagascar and areas surrounding the Red Sea and the Mediterranean Sea (Morton, 1961; Kapoor, 1990). At the present time the principal areas for production of aloes are South Africa, Venezuela, Haiti, Florida and the Dutch islands of Aruba and Bonaire. The plant grows very well if adequately protected from cold weather; aloes are injured at 2 °C and generally killed at −1 °C. The genus Aloe includes trees (e.g. A. ferox: Figure 9.1) of variable height (from 2 to
15 metres), shrubs and herbs (A. barbadensis). They are succulent plants with perennial, strong and fibrous roots and numerous (15-30) large, fleshly leaves, carrying spines at the margin. In some species the leaves form a rosette at ground level (A. perryi). The flowers are grouped in erect, terminal spikes, and are borne by a floral stalk, which is either unique (A. vera) or ramified (A. ferox); the corolla is tubular, divided into narrow segments (six) at the mouth and of a red (A. perryi), yellow (A. vera) or white (A. speciosa Baker) colour (Dezani and Guidetti, 1953). In some aloes (A. arborescens) the vascular cambium develops with age, initiating extensive secondary growth and allowing considerable lateral expansion (Cotton, 1997). Aloes resemble to some extent the agave or century plant (Agave americana L., Family
Amaryllidaceae); however, the aloe plant is in flower during the greater part of the year while the agave plant is remarkable for the long interval between its periods of flowering. Aloe leaves in section show from outer to inner: (i) a cuticularized epidermis; (ii) a
parenchyma containing chlorophyll, starch and bundles of needles of calcium oxalate; (iii) large peryciclic cells; and, (iv) a central region (3/5 of the diameter of the leaf) consisting of large parenchymatous cells.
