Diversity and Conservation through Cultivation of Hypoxis in Africa—A Case Study of Hypoxis hemerocallidea

: Africa has the largest diversity of the genus Hypoxis , accounting for 61% of the current globally accepted taxa within the genus, including some endemic species. Using Hypoxis hemerocallidea as a case study, this review addresses the conservation concerns arising from the unsustainable, wild harvesting of a number of Hypoxis species. Hypoxis hemerocallidea is one of the wild-harvested, economically important, indigenous medicinal plants of southern Africa, with potential in natural product and drug development. There are several products made from the species, including capsules, tinctures, tonics and creams that are available in the market. The use of H. hemerocallidea as a “cure-all” medicine puts an important harvesting pressure on the species. Unsustainable harvesting causes a continuing decline of its populations and it is therefore of high priority for conservation, including a strong case to cultivate the species. Reviewing the current knowledge and gaps on cultivation of H. hemerocallidea , we suggest the creation of a platform for linking all the stakeholders in the industry. of research and commercial use of Hypoxis hemerocallidea .


Introduction
The African continent is known for its rich floral biodiversity, high levels of endemism [1] and increasing reliance on its natural resources based on its indigenous knowledge systems, for economic growth and development. The increasing reliance of a growing population coupled with other factors such as habitat destruction, alien species invasion and other anthropogenic factors has resulted in an increasing strain on African plant diversity, creating the need for urgent biodiversity conservation interventions [2]. Globally, there are 119 accepted taxa, including species and infra-species levels within the genus Hypoxis [3]. Using the latest information from the African Plant database [4], there are 72 of these taxa with accepted names [3,5] that are naturally distributed in tropical Africa, southern Africa, North Africa and Madagascar (Table 1). According to Balogun et al. [6], about 40 Hypoxis species are known in southern Africa, which is regarded as the main center of the species diversity and endemism [7]. Some of the species have been grouped into another genera following recent taxonomic reclassification [3,5]. About 32 Hypoxis species were recorded in Tropical East Africa including Uganda, Kenya, and Tanzania [8]. Hypoxis species are regarded as valuable medicinal plants for the treatment of numerous ailments in most parts of Africa [9]. In southern Africa, Hypoxis hemerocallidea is the top Hypoxis species with commercial value, seconded by H. colchicifolia [10,11]. This review therefore

Hypoxis Species in Africa
The African continent alone accounts for 61% (N = 72) of the current globally accepted taxa within the genus Hypoxis.  [8]. Many Hypoxis species are used in the management of HIV/AIDS, cancer, tuberculosis, sexually transmitted diseases and infertility ( Table 1), because of their similarity in chemical constituents [18]. As a result, some of these taxa are used interchangeably in African Traditional Medicine [8]. For example, H. angustifolia Lam, H. goetzei Harms, H. nyasica Baker, and H. obtusa Burch. ex Ker Gawl. are all used in traditional medicine for similar purposes in Tanzania [7]. The corm is often the plant part used and its harvest is rather unsustainable and might lead to decimation of natural populations. At present, only Hypoxis malaissei Wiland has been listed in the IUCN Red List of Threatened Species [19] as 'Data Deficient'. However, this species and H. fischeri var. katangensis (De Wild.) Wiland & Nordal are suggested to be in the East Tropical Africa 'Critically Endangered' list [8]. Most species only appear on National Red List Data as 'Least Concern', but H. fischeri var. colliculata (Wiland) Wiland & Nordal, H. kilimanjarica Baker, H. kilimanjarica subsp. Prostrata., and H. polystachya Welw. ex Baker are listed as 'Vulnerable' in the East Tropical Africa [8], and five other species are listed as 'Near Threatened' (Table 1).

Natural History and Distribution of Hypoxis hemerocallidea
Hypoxis hemerocallidea, previously known as H. rooperi [3,5], is a perennial corm with long, broad, and slightly hairy leaves [34,35] (Figure 1). Some species have a close morphological resemblance with H. hemerocallidea, such as H. acuminata Baker, H. colchifolia Baker, H. galpinii Baker, and H. obtusa [36]. The long, hairy and sickle shaped leaves of H. hemerocallidea differentiate it from the other species [36]. Hypoxis hemerocallidea has yellow star-shaped flowers [36], of which between one to three open within an interval of an hour per day, a strategy to encourage cross-pollination [37]. Although H. hemerocallidea plants produce many seeds, very low germination percentages were reported [38], due to the hard, shiny, black seed coat which may be impermeable to water and may restrict oxygen movement to the embryo, thus delaying germination [37,38]. Most mature corms, which are darkbrown to black outside and yellow inside, are approximately 10-15 cm in diameter and about half a kilogram in weight [39]. The fleshy corm is a survival mechanism that enables the plant to withstand cold conditions, drought, and veld fire [40]. In South Africa, H. hemerocallidea grows naturally in the savanna grasslands in KwaZulu-Natal, Eastern Cape, Mpumalanga, Limpopo, Gauteng, and Free State Provinces, and also grows in other countries such as Lesotho, Swaziland, Mozambique, and Zimbabwe [41].

Uses and Chemical Composition of Hypoxis hemerocallidea
Hypoxis hemerocallidea is traditionally used as a tonic, purgative, diuretic or to treat infertility, inflammation, prostate gland disorder, wounds and burns [14,42]. Promising anticancer activities of H. hemerocallidea have also been reported [43], which support the listing of H. hemerocallidea as one of the species used for the treatment of cancer in the Eastern Cape Province of South Africa [44]. Furthermore, it is also used for the treatment of diabetes in Eastern Cape and Eastern Free State [6,16]. The species was made famous by the South African Health Ministry when it was recommended as an immune booster for people living with HIV/AIDS [16,44,45]. The 14 member states of the Southern African Development Community (SADC) supported the use of 'African potato' in HIV management [46]. Hypoxis hemerocallidea was found to be a good source of trace elements such as zinc, copper, and manganese, which could account for its use as a pro-fertility ingredient and for boosting the immune system [47]. However, there are warnings of a potential herb-drug-interaction if H. hemerocallidea is used with conventional drugs for the management of HIV/AIDS [45]. It was also mentioned as one of the three most used plant species in the treatment of sexually transmitted diseases, in KwaZulu- Hypoxis hemerocallidea has yellow star-shaped flowers [36], of which between one to three open within an interval of an hour per day, a strategy to encourage cross-pollination [37]. Although H. hemerocallidea plants produce many seeds, very low germination percentages were reported [38], due to the hard, shiny, black seed coat which may be impermeable to water and may restrict oxygen movement to the embryo, thus delaying germination [37,38]. Most mature corms, which are dark-brown to black outside and yellow inside, are approximately 10-15 cm in diameter and about half a kilogram in weight [39]. The fleshy corm is a survival mechanism that enables the plant to withstand cold conditions, drought, and veld fire [40]. In South Africa, H. hemerocallidea grows naturally in the savanna grasslands in KwaZulu-Natal, Eastern Cape, Mpumalanga, Limpopo, Gauteng, and Free State Provinces, and also grows in other countries such as Lesotho, Swaziland, Mozambique, and Zimbabwe [41].

Uses and Chemical Composition of Hypoxis hemerocallidea
Hypoxis hemerocallidea is traditionally used as a tonic, purgative, diuretic or to treat infertility, inflammation, prostate gland disorder, wounds and burns [14,42]. Promising anticancer activities of H. hemerocallidea have also been reported [43], which support the listing of H. hemerocallidea as one of the species used for the treatment of cancer in the Eastern Cape Province of South Africa [44]. Furthermore, it is also used for the treatment of diabetes in Eastern Cape and Eastern Free State [6,16]. The species was made famous by the South African Health Ministry when it was recommended as an immune booster for people living with HIV/AIDS [16,44,45]. The 14 member states of the Southern African Development Community (SADC) supported the use of 'African potato' in HIV management [46]. Hypoxis hemerocallidea was found to be a good source of trace elements such as zinc, copper, and manganese, which could account for its use as a pro-fertility ingredient and for boosting the immune system [47]. However, there are warnings of a potential herb-drug-interaction if H. hemerocallidea is used with conventional drugs for the management of HIV/AIDS [45]. It was also mentioned as one of the three most used plant species in the treatment of sexually transmitted diseases, in KwaZulu-Natal and Limpopo Provinces of South Africa [48,49]. In support of its traditional use as an anti-miscarriage medicine, apart from being used for bronchial asthma [50], a study by Nyinawumuntu et al. [51] showed that H. hemerocallidea corm extracts possess uterolytic activity. Hypoxis hemerocallidea is mentioned as one of the species used for the treatment of tuberculosis in Limpopo Province of South Africa [52]. The species was one of the most cited medicinal plants in the medicinal markets [53], used for treatment of malaria and venereal diseases in Mozambique [26,54]. Different Hypoxis spp. are used in the treatment of prostate cancer in Zimbabwe [55]. A description of the history, first research reports and prominent promotion of commercial uses of H. hemerocallidea [43] is adapted in Figure 2. Traditional uses and chemical constituents of 11 Hypoxis species, including 14 H. hemerocallidea herbal formulations indicating the commercial importance of this species, are summarized in other reports [56].
Hypoxis hemerocallidea, H. rigidula Baker, H. galpinii, and H. obtusa showed similar phytochemical profiles, although further studies were recommended to confirm their safety [60]. A higher concentration of ergosterol and stigmasterol was reported in H. rigidula when compared to H. hemerocallidea [62]. When H. hemerocallidea was compared to H. stellipilis Ker Gawl. and H. sobolifera Jacq., it was found that both sterol and hypoxoside contents varied amongst the species, which questions the indiscriminate use of Hypoxis spp. in traditional medicine [60]. Several studies have been conducted to investigate the hypoglycaemic effects [63,64], typhlocolitic effects [65] and its effects on pharmacokinetics of efavirenz [57], antibiotic and immune modulation phytotherapies [66].
The common name 'African potato' is misleading, as many perceive H. hemerocallidea as edible. Hypoxis hemerocallidea has been reported as one of the indigenous and traditional food crops consumed in the North West Province of South Africa [67]. This species could be confused with the edible Plectranthus esculentus N.E.Br. as they both share the same common name of 'African potato' [67]. Hypoxis hemerocallidea has low crude protein value and low accumulation of selected elements [68], compared to human daily requirement, but its high iron content makes it a good candidate for use in overcoming iron deficiencies [47]. Some geophytes of Hypoxis were found in the caves in South Africa, evidence for cooking of edible rhizomes centuries ago [69]. Diversity 2020, 12, x FOR PEER REVIEW 11 of 21 A glycoside called hypoxoside is mentioned as the main component of H. hemerocallidea, with sterols (stigmasterol, β-sitosterol, campesterol), sterolins, norlignan, daucosterols and stanols (stigmastanol) as additional constituents [42,46,[57][58][59]. Amongst these phytochemicals, daucosterols, β-sitosterol, and hypoxide are associated with the plants' therapeutic activities [60]. Phenylalanine and t-cinnamic acid are reported to be precursors of hypoxoside in whole H. hemerocallidea plants [61]. Although some studies have proved that Hypoxis extracts with 45% hypoxoside are not toxic

Market Demand of Hypoxis hemerocallidea
Products incorporating extracts of medicinal plants such as H. hemerocallidea, which were used solely in traditional medicine are increasinlgy becoming commercialized [70]. The first Hypoxis hemerocallidea product was developed in 1967, in Johannesburg, South Africa and was successfully marketed in Germany [71]. An increase in the market share of H. hemerocallidea and H. colchifolia in 2001 was attributed to the publicity of the species received after several media releases proclaiming its healing properties [72]. Even before this increase in consumption, it was found that 77% of the Hypoxis corms sold in the Witwatersrand informal medicinal plant markets were 2-7 cm in diameter, with traders compensating for the smaller size by selling a large number of smaller corms [72]. This could be an indication of the depletion of bigger corms in the wild, leading to smaller immature bulbs being harvested. For example, the size of Eucomis autumnalis (Mill.) Chitt bulbs sold in the market, decreased in size between 1995 and 2001, indicating the negative impacts of harvesting for trade [72]. Nevertheless, pressure on this resource continues as Hypoxis spp. (H. hemerocallidea and H. colchifolia) were ranked fourth in terms of volumes sold in 2007, at the Faraday market in Johannesburg [72] and was one of the 19 species that had a high demand in Zululand market [73]. 'African potato' was one of the top 10 most frequently sold medicinal plant species, reaching 11,000 kg/annum to the value of R 322,500 (approximately 21,930 USD; at the 2019 average rate of R 1.00 = 0.068 USD), in Eastern Cape Province of South Africa [74]. Approximately 31,300 corms of H. hemerocallidea were sold annually from 54 outlets in Durban, South Africa [75]. A factory in KwaZulu-Natal (South Africa) was reported in 2004 to be processing 1.5 tons of H. hemerocallidea derived products and this was expected to increase annually [29]. In Lesotho, H. hemerocallidea was mentioned as one of the medicinal plants frequently used for a wide range of ailments [76]. This plant was the second most commonly used species in Kimberly, South Africa [77]. In Maputo, Mozambique, H. hemerocallidea topped the list of medicinal plant species mentioned by 71% of traders interviewed [78]. Figure 3 shows H. hemerocallidea corms displayed at an informal market in northern KwaZulu-Natal, South Africa.
Many products made from H. hemerocallidea, which include capsules, tinctures, tonics and creams, are available in the market [79]. Hypoxis hemerocallidea is exported, in a preprocessed form, to Asia and Europe, where the extracts are used for treatment of prostate problems [14]. In a review on medicinal plants with potential in the development of drugs, H. hemerocallidea is mentioned as one of the famous African medicinal plants [80] with an ever-increasing demand.

Conservation Status of Hypoxis hemerocallidea
The conservation status of H. hemerocallidea is described as declining, and although not endangered with extinction, harvesting would cause a continuing decline of its populations and it is therefore of priority for conservation [40,81], with frequent monitoring warranted [74]. The only conservation effort was reported in KwaZulu-Natal, South Africa, where 250 hectares of land has been reserved for protection of H. hemerocallidea [81].
The use of H. hemerocallidea as an "all-purpose", "cure-all", or "wonder plant" medicine [37,50] has put pressure on wild populations because it presents an opportunity for income generation,

Conservation Status of Hypoxis hemerocallidea
The conservation status of H. hemerocallidea is described as declining, and although not endangered with extinction, harvesting would cause a continuing decline of its populations and it is therefore of priority for conservation [40,81], with frequent monitoring warranted [74]. The only conservation effort was reported in KwaZulu-Natal, South Africa, where 250 hectares of land has been reserved for protection of H. hemerocallidea [81].
The use of H. hemerocallidea as an "all-purpose", "cure-all", or "wonder plant" medicine [37,50] has put pressure on wild populations because it presents an opportunity for income generation, through species-specific trade network [56]. During harvesting, the whole plant is uprooted, resulting in total destruction of the plant [75]. There is a need for urgent propagation intervention [73] as their populations in the wild are declining [1]. For example, in Swaziland, H. hemerocallidea has become threatened with extinction [82]. In an effort to come up with sustainable harvesting strategies, Katerere and Eloff [83] found that H. hemerocallidea leaves cannot be used as a substitute for the corms due to lack of similarities in phytochemical content and bioactivity. However, it was suggested that the leaves of H. hemerocallidea might be used as substitutes for the corm in the treatment of some bacterial and fungal diseases as there seemed to be a shift in activity between plant organs in different seasons [56]. Hypoxoside was reported to be hydrolysed in the leaves and then transported to the corms [61], with this activity shifting from the leaves to the corms in summer [56]. Du Toit et al. [84] reported that harvesting season affected the concentration of active ingredients produced from the corms during the year. Therefore, the correct timing of collection of H. hemerocallidea leaves could ease the pressure off wild populations. The activity was higher in the leaves in spring [56], a period in which the corms are regrowing the leaves after a period of dormancy when there are fewer or smaller leaves available. In summer, when there is a greater number of bigger leaves, the activity is shifted to the corms and this could be another reason for continued use of the corms than the leaves.

Propagation and Cultivation of Hypoxis hemerocallidea
Due to the value of H. hemerocallidea in traditional medicine and the likely diminishing wild populations, there is a strong case to cultivate the species for sustainable supply of good quality corms [35,45,75], agreeing with Katerere and Eloff [83] who mentioned that the only viable alternative to unsustainable wild harvesting of H. hemerocallidea is propagation and domestication. In essence, cultivation will not only alleviate pressure on natural resources, but it also has practical implications on optimising secondary metabolite production, facilitating standardisation, and increased safety by reducing inconsistency in quality and composition of plant material, reducing the risk of adulteration and increasing yield through management practices [85]. Encouragement of cultivation of wild harvested medicinal plants and development of nurseries to propagate the species will take off the pressure on wild stocks [44]. Cultivation of medicinal plants is becoming popular, with increasing government support to meet the high demands for plant materials [86]. The bioprospecting economy and related strategies in South Africa have put an important drive to mass propagation and cultivation of commercially important medicinal plants, of which H. hemerocallidea is within the top 25. However, one of the major factors hindering the improvement in cultivation of H. hemerocallidea is lack of knowledge of its agronomic and quality traits [40].
Propagation of H. hemerocallidea was identified as problematic since seed dormancy is difficult to be broken and the species does not propagate easily from corms; thus studies relating to reproductive biology and seed physiology of the species were recommended as a priority [12,40]. Seed germination of H. hemerocallidea is also a barrier because of unpredictable seed viability, combinational dormancy, poor seedling establishment, while vegetative propagation is rare [38]. Micropropagation of H. hemerocallidea is the only vegetative propagation method that has been thoroughly studied by many researchers [87]. Corm explants of H. hemerocallidea seem to take at least nine weeks to respond positively in in vitro culture compared to other Hypoxis species [88]. Other challenges with in vitro propagation of H. hemerocallidea include browning of explants and nutrient medium which necessitates regular subculturing of the shoots at six weeks' interval [81]. Endogenous contamination was also reported as a major challenge when underground organs were used as explants [75]. Ndong et al. [40] explored the regeneration potential of H. hemerocallidea corm explants by inoculating them on culture media with a wide range of plant growth regulator combinations and concentrations. The study concluded that no shoots were formed without plant growth regulators; shoot formation frequency and intensity were mainly dependent on cytokinin concentration and the best results were obtained with kinetin than with benzylaminopurine (BA). In a similar study, Nsibande et al. [89], reported that corm explants of H. hemerocallidea were very slow and relatively poor in responding to in vitro culture, with the majority of the treatments forming no callus, compared to other three Hypoxis spp. (H. filiformis, H. argentea,  and H. acuminata). Direct shoot development started 10 weeks after transferring of the corm explants to a Murashige and Skoog medium supplemented with cytokinins, although growth of the shoots was prolonged [89]. Cytokinins have been reported to have a promoting effect on shoot formation in tuberous plants including Hypoxis spp. [40]. The stimulation of shoot regeneration, proliferation and growth by cytokinins is a species-dependent phenomenon, which is influenced by structure-activity relationship, cytokinin homeostasis, concentration of inherent endogenous plant growth regulators and auxin-cytokinin cross-talk [81]. Somatic embryogenesis, which involves the development of embryos from normal plant tissue, with the use of 2,4-D and BA produced a high number of somatic embryos while GA 3 was successful in developing the somatic embryos into plantlets [79].
Seedling emergence of H. hemerocallidea was observed a year after sowing [38]. Gillmer and Symmonds [90] have successfully germinated a large number of H. hemerocallidea seed by watering them three times in a day. In other experiments, there was no germination of intact seeds of H. hemerocallidea at three different temperatures (20,25, and 30 • C), even when the seeds were treated with several chemicals [38]. Complete removal of the seed coat with incubation at 20 • C under white light resulted in 36% germination compared to dark conditions where only 6% germinated [38]. Seed coat seem to inhibit prompt germination of H. hemerocallidea seeds. Gibberellic acid (GA 3 ) at 10 −3 mol dm −3 increased germination of coatless seeds, at 25 • C [37], as well as mechanical scarification and subsequent soaking for 24 h in 50 mL of GA 3 at 1200 ppm, which increased germination to 60% [38]. The scarification could have removed the physical barrier, while the GA 3 could have broken the embryo dormancy. The positive effect of GA 3 further suggests the presence of embryo dormancy in addition to the physical dormancy. For example, seeds harvested in early November (early summer) from Mountain Rise in KwaZulu-Natal (KZN), South Africa, reached a germination percentage of 52% at 25 • C, compared to 16% and 9% achieved from seeds harvested at the same site in early December and early January (mid-summer) [35]. The study by Hammerton et al. [35] suggests that microclimates and differences in soil conditions from different sites may have affected seed viability and dormancy. Seeds collected from a second site (Hayfields in KZN) in late December only achieved approximately 13% germination [35].
Although work has been done on in vitro propagation and seed germination of H. hemerocallidea, there is a need to develop methods that can supply the market with the material at reasonable costs [41]. In an effort to develop an easy and affordable propagation method for H. hemerocallidea, chipping into equal segments and scooping to remove the growth tip were found to be effective propagation methods [87].
Care is also needed as H. hemerocallidea plants to which herbicides were not applied grew better and had a higher hypoxoside content, compared to herbicide-treated plants [91]. Competition with weeds could have led to plant stress and thus an increase in secondary metabolite synthesis. It seems that high levels of nutrients (N, P, and K) are only required initially to produce a suitable H. hemerocallidea biomass and after plant establishment, fertilizer treatment can be discontinued [91]. Although H. hemerocallidea prefers poor soils with little nutrients, site selection for cultivation of the species is essential as exposure to cadmium (Cd) and aluminium (Al) significantly decreased the accumulation of hypoxoside [86]. Du Toit et al. [84] found that growing media and harvesting season affected the amount of compounds or active ingredients produced from the corms during the year.

Gaps in Cultivation Research of Hypoxis hemerocallidea
Currently, cultivation information, including the response of H. hemerocallidea to agronomic practices, is limited to few studies. Although H. hemerocallidea seems to be a drought-tolerant species, there is no official record of it growing in the Northern Cape and Western Cape Provinces of South Africa (Figure 4). According to the South African National Biodiversity Institute (SANBI), the species mostly grows in areas having 600 to 1000+ mm/annum rainfall, which includes the semi-arid and dry-sub humid zones of South Africa, with warm temperate climate, cool to hot summers, and humid to dry winters [92]. This indicates a need to investigate watering requirements from the seedling establishment stage to maturity. Imposing water stress at specific growth stages or even for a specific period before harvesting could increase growth while ensuring good content of active compounds. Ideally, cultivation at a commercial scale, provides an opportunity for manipulation of growing conditions to shorten the period to reach maturity, increase potency and predictability of extracts. Pelargonium sidoides DC. plants grown under greenhouse conditions, for example, showed equivalent concentrations of the compound of interest, umckalin, and approximately six times greater growth rates [93]. Excessive watering (twice and thrice a week) of Dioscorea dregeana (Kunth) T. Durand & Schinz seedlings reduced vegetative growth but significantly improved seedling weight and tuber size, while watering once a week resulted in better above ground biomass [94].  The effect of fertilizers or exposure to different nutrient status on growth and medicinal activity of H. hemerocallidea is not fully understood. For example, in Siphonochilus aethiopicus (Schweif.) B.L. Burt, plants exposed to low nitrogen levels with severe water stress showed increased flavonoids, phenolics, and antioxidants indicating that fertilizer application and irrigation can alter secondary metabolite content [95]. Understanding of the strategies employed by H. hemerocallidea under water and nutrient stress conditions in relation to its growth, physiology, and secondary metabolite production is important. Furthermore, field observations by Mofokeng et al. [96] showed that cultivated Pelargonium sidoides was susceptible to root-knot nematodes, such that root yield was negatively affected. The quality of H. hemerocallidea corms could be negatively affected if the species can be found to be susceptible to root-knot nematodes. Figure 5 shows a potential pest (African bollworm: Helicoverpa armigera Hübner) of H. hemerocallidea, feeding on the leaves and seeds, observed in a small scale plantation. The effect of fertilizers or exposure to different nutrient status on growth and medicinal activity of H. hemerocallidea is not fully understood. For example, in Siphonochilus aethiopicus (Schweif.) B.L. Burt, plants exposed to low nitrogen levels with severe water stress showed increased flavonoids, phenolics, and antioxidants indicating that fertilizer application and irrigation can alter secondary metabolite content [95]. Understanding of the strategies employed by H. hemerocallidea under water and nutrient stress conditions in relation to its growth, physiology, and secondary metabolite production is important. Furthermore, field observations by Mofokeng et al. [96] showed that cultivated Pelargonium sidoides was susceptible to root-knot nematodes, such that root yield was negatively affected. The quality of H. hemerocallidea corms could be negatively affected if the species can be found to be susceptible to root-knot nematodes. Figure 5 shows a potential pest (African bollworm: Helicoverpa armigera Hübner) of H. hemerocallidea, feeding on the leaves and seeds, observed in a small scale plantation.
Other important aspects of commercial cultivation of H. hemerocallidea include optimum size and timing before harvesting the species, as it is not clear at what age or size are the medicinally active compounds available or optimum in the corm. In general, the target compounds in medicinal plants are secondary metabolites which serve as an adaptation strategy to environmental stress, infection, or herbivory. Thus, agronomic practices that can manipulate the growth and synthesis of secondary metabolites in H. hemerocallidea need to be fully understood if the species is to be successfully cultivated.
phenolics, and antioxidants indicating that fertilizer application and irrigation can alter secondary metabolite content [95]. Understanding of the strategies employed by H. hemerocallidea under water and nutrient stress conditions in relation to its growth, physiology, and secondary metabolite production is important. Furthermore, field observations by Mofokeng et al. [96] showed that cultivated Pelargonium sidoides was susceptible to root-knot nematodes, such that root yield was negatively affected. The quality of H. hemerocallidea corms could be negatively affected if the species can be found to be susceptible to root-knot nematodes. Figure 5 shows a potential pest (African bollworm: Helicoverpa armigera Hübner) of H. hemerocallidea, feeding on the leaves and seeds, observed in a small scale plantation. Other important aspects of commercial cultivation of H. hemerocallidea include optimum size and timing before harvesting the species, as it is not clear at what age or size are the medicinally active compounds available or optimum in the corm. In general, the target compounds in medicinal plants are secondary metabolites which serve as an adaptation strategy to environmental stress, infection,

Conclusions
The decline in wild populations and the increasing demand for H. hemerocallidea present an opportunity to cultivate the species for conservation purposes but also as an alternative cash crop for different communities. Sustainable harvesting methods and the use of leaves as an alternative to corms should be further researched, including increasing leaf biomass and manipulating active compound content in the leaves. The main challenges for cultivation of H. hemerocallidea, as with many perennial medicinal plants, are the relatively long period before harvesting, in competition with wild harvest, which may reduce prices, and spatial-temporal competition with food crops. Opportunities are increasing since government legislation on wild harvesting is becoming stricter; as the demand for natural health products is also increasing, and with cultivation, pharmaceutical companies are assured of reliable supply of quality material. For example, the South African government has started to promote cultivation of commercially important indigenous medicinal plants and created a platform for linking all stakeholders in the industry. Furthermore, funding for initial investment, which is a big problem for rural poor farmers, can be made available through the abovementioned platform. As the current wild harvesting of H. hemerocallidea is probably unsustainable and considering its substitution with other Hypoxis species, it is imperative that population studies of many African Hypoxis species and their conservation status be reviewed for more information in order to facilitate timeous conservation and management strategies.