The uses of Kenyan aloes: an analysis of implications for names, distribution and conservation

Aloes are easily distinguished from other plants by their characteristic succulent spiny leaves, and thus it is not surprising that the local naming at the genus level is consistent with the scientific species concepts. However, a species may be given two names to reflect the appearance or use of the plants. When two species have the same vernacular name, they also share the way of use, and the local people therefore have no practical need to distinguish the species.

The vernacular names of Aloe species in Kenya are closely linked to use. In all areas where the widespread and widely used A. secundiflora occurred, this species was referred to as “the aloe” or “the real aloe”. In our study region, relatively few species of Aloe co-occur, making the recognition of Aloe secundiflora sufficient to distinguish the other species from “the real one” by descriptive characteristics like “the tall aloe” or “the grey aloe”. This naming also reflects the importance of the different species to the local communities; the “real aloe” is the most important aloe, and the other species are less important. If an aloe is not of any specific use, it is often not given any name at all. When the respondents were asked for names of some these species, they responded: “it is an aloe, but not a real one”. Our observations of vernacular nomenclature applied to Aloe spp. and overlap with scientific species concepts agree broadly with previous studies that have reported a binomial system in which vernacular names describe the plant name and its use [34, 35].

Aloe secundiflora and A. lateritia were the most important Aloe species in our study area according to the respondents, and this is evident in the wide variety of uses listed for these species. Several informants said, when describing the uses of Aloe lateritia, that it was used when A. secundiflora was not available. They further claimed that the Aloe lateritia is not as bitter as A. secundiflora, and hence not as effective. These two species are the most widespread in our study area, and thus have the greater potential of being used compared to other more geographically restricted species (Fig. 3). The different traditions of the nine ethnic groups surveyed contributed to increasing the diversity of uses recorded for these widespread species. Aloe secundiflora and A. lateritia are the only species of Aloe that are found in almost all of the seven Flora regions (Flora of Tropical East Africa K1- K7 Fig. 1b, [8]). Most aloes in Kenya are geographically restricted, but might at the same time be locally common [8, 11]. This is the case for species like Aloe aageodonta L.E.Newton and A. chrysostachys Lavranos & L.E.Newton, which are found only in the Flora region K4. The respondents used these species in more or less the same way as Aloe secundiflora in other areas. But where the two species (Aloe secundiflora and A. lateritia) were readily available, these were mostly preferred. Interestingly, other ethnobotanical studies elsewhere in Kenya and Uganda reported that the use of mixtures of medicinal plants, including Aloe spp., is much less common than the use of single-species preparations [35‐37]. Poisonous members of the genus, like Aloe ballyi Reynolds and also A. elata S.Carter & L.E.Newton, which are used by people for arrow poison, are known to contain toxic hemlock alkaloid γ-coniceine [29], are generally avoided by humans and cattle.

Two uses were emphasized by respondents in each of the nine ethnic groups: the use of Aloe species for the treatment of malaria and for poultry diseases. These findings are supported by pharmacological studies e.g. [30, 31] and ethnobotanical studies in Kenya that have reported malaria as the greatest medical concern treated with herbal remedies e.g. [35]. Similarly, aloes feature prominently in ethnoveterinary medicine throughout their range and are most valued for their uses against insect pests [26, 34, 36]. The relative importance of Aloe in ethnomedicine and ethnoveterinary medicine should be understood in the regional context; in some areas of East Africa, herbal treatments are the only option for up to 80 % of the population [14].

Our data suggest that knowledge about the uses of Aloe species is commonly held among community members in Kenya, and knowledge is distributed evenly across ages and gender. That the Maasai and Kamba ethnic groups listed the highest numbers unique use records, might only be a reflection of the relative higher species diversity within their residential areas. Aloes are renowned internationally and some of the formally educated respondents claimed that the name of the local aloe (most often A. secundiflora) was A. vera, and that it was indigenous to Kenya. Public opinion about A. vera as “a wonder drug” has therefore been transferred to local aloes. In contrast to a general belief that all aloes are used wherever they grow [16] we could not find any documentation of use for 63 % of the Kenyan aloes (Fig. 5). The extent to which a species is uses is a result of the combination of availability and suitability for a particular purpose. Widespread species of Aloe are generally more frequently used than geographically restricted species, and uses are influenced by the growth form of the aloes. The shrubby A. ngongensis, A. kedongensis Reynolds and A. nyeriensis and the small tree A. volkensii Engl. are more suitable for fencing and hedging than the smaller and acaulescent species.

Species that are only found at one or few remote localities appear to be overlooked because people do not have easy access to the plants. However, some species that are relatively accessible are not used. Three (A. classenii Reynolds, A. penduliflora Baker and A. vituensis Baker) out of a total of 19 species documented in this study had no reported use. A few species had very limited use, such as A. fibrosa Lavranos & L.E.Newton and A. elata, for which the only reported use was as ornamentals. One special case is the very widespread A. myriacantha (Haw.) Schult. & Schult. f. (Fig. 5). Being a “grass aloe” it lacks the typical succulent leaves that people use. Succulent leaves have been positively correlated with the likelihood that an Aloe species is used for medicine [38]. Dying back in the dry season, people probably do not regard this as an aloe at all.

Local knowledge of natural resources has been recognised as an important element of effective conservation strategies in Kenya [37]. We found no significant connection between high numbers of recorded uses and perceived decreases in Aloe population sizes. Harvesting practices differ markedly in their impact on the Aloe plant: only small pieces of the leaves are used for the various medical uses while, in contrast, the whole plant is dug up when the stems are used for making beer, or the entire plant for fodder. However, we found no correlation between decrease in aloe populations and either the tradition of beer-making or the use aloes for fodder. This might indicate that local harvesting in general is done on a sustainable basis, and that habitat destruction due to increase in human and livestock populations poses a more urgent threat to Aloe species Kenya. Indeed, changes in land use were the most frequently given reasons for perceived declines in Aloe populations. Another factor that could be influential is that the most used species Aloe secundiflora is very common: a survey done by Mukonyi et al. (Mukonyi KW, Situma CA, Lusweti A, and Kyalo, S. Sustainable utilization of commercial Aloe resources in the drylands of Kenya 2005. Unpublished report) estimated the Kenyan population of commercial aloes at 129 million plants, 83 % of which were A. secundiflora. With such an abundant species, declining availability should be quickly noticeable. However, several respondents reported that they have to walk longer distances than before to collect their medicine from an Aloe population. As a consequence, aloes are more frequently planted in residential compounds to ensure the plants are accessible when they are needed (Fig. 4c). Local people are actively propagating seeds and replanting plantlets from other populations, conserving the local genetic diversity of Aloe species. Further, several informants responded that when moving from another area they had brought the aloes with them, indicating that the most-used aloes also are spread by humans. The succulent leaves allow aloes to survive for a long time out of soil, and the practice of moving aloes is well known [16]. Aloe vera, in particular, is an example with highly expanded distribution due to use, and was spread from the Arabian Peninsula along the trade routes to the Mediterranean, India, Americas and Caribbean [1, 38].

There is a close connection between the diversity of use and geographical distribution of Aloe species in Kenya (Figs. 3, 5). Not surprisingly, the wider the distribution range is for a species, the higher the number of uses documented for it. A species' range is also correlated with the number of ethnic groups that may use a species; in this study, A. lateritia and A. secundiflora were used by 8 and 7 ethnic groups, respectively (Fig. 2). At the other end of the scale, about 50 % of the species were used by only one ethnic group. In our study area, 16 of a total of 19 species were used (84 %), in contrast to the overall use in Kenya where only 23 out of 63 species of Aloe (37 %) are documented to be used. We propose that this disparity is due to the high number of rare species of Aloe in Kenya, which are often found in remote areas. In inhabited areas, the aloes undoubtedly play a very important role for the society, people and their livestock.