Encephalartos Species Research Articles

Resource dilution effect rather than resource concentration hypothesis explains the patterns of pre-dispersal seed predation of an African cycad along an elevational gradient in South Africa.

The genus Encephalartos is entirely endemic to Africa, and like most cycad species, the genus is at risk of extinction. One of the threats jeopardising the future of the genus is reproduction failure, a failure that is still poorly understood. Our objective was to investigate what predisposes Encephalartos species to seed damages through predation, a potential cause of reproduction failure. We collected functional traits of 430 individuals of Encephalartos villosus, as well as data on pre-dispersal seed predation, habitat type and elevation in the Origi Gorge Nature Reserve, South Africa. Then, we analysed our data by fitting a structural equation model. We found that plants tend to be taller when moving from open to close habitat, whereas plant height tends to increase along elevation. In addition, taller plants tend to have more leaves, and plant canopy size shows significant positive relationship with elevation, plant height and number of leaves. These findings suggest a leaf height-canopy dimension strategy perhaps in response to environmental stresses imposed by elevation. We tested the effects of habitat types on seed production. Although there were significantly more seeds in open habitats, open habitats showed the lowest proportion of predated seeds. Finally, we tested the effects of elevation on seed production. We found that seed production decreases along elevation while the proportion of predated seeds increases. Under the resource concentration hypothesis, these findings (where there are more resources, predation is low) are unexpected, suggesting rather that it is the resource dilution effect that matches the pre-dispersal seed predation patterns in our study area. We suggest that anthropogenic pressures at lower elevation due to easy access may cause seed predators to shift towards higher elevation where they cause heavier damage to seed, thus perhaps contributing to the extinction risk of the genus Encephalartos.

CLIMATIC CHANGES MAY NOT AFFECT THE DISTRIBUTION RANGE OF SOUTH AFRICAN ENDEMIC ENCEPHALARTOS SPECIES (CYCADALES)

In recent decades climate change has emerged as one of the major forces driving biodiversity loss and species extinction. Cycads are highly threatened species and previous studies have revealed they are also being affected by climate change. In this study we tested the possible response to climate change of four rare cycad taxa (Encephalartos species) endemic to South Africa, displaying a low but reasonable number of natural occurrences. Maximum Entropy model (MaxEnt) was used in carrying out the predictions based on eight environmental variables. Our results revealed no range contraction but a slight spread in the distribution of these taxa. Temperature seasonality, vegetation types and landforms are by far the most important predictors of the species modelled. On the contrary, the mean annual temperature and precipitations showed very low contributions in all models. We conclude that climate change may not determine a reduction in range size of the Encephalartos species studied. Possible decline in South African cycads may still occur through anthropogenic influences.

Cycad forensics: leaflet micromorphology as a taxonomic tool for South African cycads

Cycads, a primitive group of gymnosperms, are currently facing extinction in many parts of the world. In South Africa, this is largely attributed to the illegal poaching of many threatened species. In the illegal trade of cycads, many highly threatened species are often deliberately misnamed as a more common species. Due to macromorphological similarity between many Encephalartos species, as well as taxonomic uncertainties that exist, species identification is also problematic. This study compared the utility of selected leaflet micromorphological characters as a taxonomic tool to independently identify eight South African cycad species. The characters, which included trichome type (if present), stomatal density and dimensions, stomatal band width and vein band width, were compared within four pairs of macromorphologically similar species. Quantitative and qualitative data on the characters were collected using stereomicroscopy, scanning electron microscopy (SEM) and variable pressure SEM. Results indicated that the majority of these characters varied significantly (p < 0.05) between paired species. Importantly, the presence of trichomes on mature leaflets of four species appears to be previously unreported. Trichome type, stomatal width and band width, and vein band width were identified as diagnostic characters that may be used to distinguish between species. The results validate the use of leaflet micromorphological characters, particularly stomatal and vein band widths (given the ease with which they can be measured), for distinguishing between macromorphologically similar cycad species.

African Cycad Ecology, Ethnobotany and Conservation: A Synthesis

Africa hosts a rich assemblage of cycads: 66 Encephalartos species, Stangeria eriopus and Cycas thouarsii. Most Encephalartos and S. eriopus adults appear to be fire-tolerant, and certain Encephalartos species may be fire-dependent. Four Encephalartos species and S. eriopus are primarily insect-pollinated. African cycad populations typically have sex ratios of 1:1, with very small populations often male-biased. Coning is typically infrequent and erratic, with many species exhibiting mast-seeding. Viable seed production in Encephalartos populations tends to decline with decreasing population size, and seed predation by weevils is common. Seed dispersal in Encephalartos is usually localized, but vertebrates may facilitate dispersal over longer distances. Stem material of 25 Encephalartos species and S. eriopus is used for traditional medicine, primarily in South Africa. Two-thirds of Africa’s cycad species are threatened, with four species already Extinct in the Wild. The illegal acquisition of cycads from wild populations is the principle threat to their persistence. Further research is recommended on seed and fire ecology, population dynamics, and the outcomes of conservation interventions.

Investigations into Encephalartos insect pests and diseases in South Africa and identification of Phytophthora cinnamomi as a pathogen of the Modjadji cycad

South Africa holds the greatest diversity of Encephalartos species globally. In recent years several reports have been received of Encephalartos species in the country dying of unknown causes. The aim of this study was to investigate the presence of, and identify the causal agents of, diseases of Encephalartos species in the Gauteng and Limpopo Provinces of South Africa. Plant material with symptoms and insects were collected from diseased plants in private gardens, commercial nurseries and conservation areas in these regions. Insects collected were identified based on morphology, and microbial isolates based on morphology and DNA sequence data. Insect species identified infesting cultivated cycads included the beetle Amorphocerus talpa, and the scale insects Aonidiella aurantii, Aspidiotus capensis, Chrysomphalus aonidum, Lindingaspis rossi, Pseudaulacaspis cockerelli, Pseudaulacaspis pentagona and Pseudococcus longispinus. Fungal species isolated from diseased plants included species of Diaporthe, Epicoccum, Fusarium, Lasiodiplodia, Neofusicoccum, Peyronellaea, Phoma, Pseudocercospora and Toxicocladosporium. The plant pathogen Phytophthora cinnamomi was identified from E. transvenosus plants in the Modjadji Nature Reserve. Artificial inoculation studies fulfilled Koch's postulates, strongly suggesting that P. cinnamomi is responsible for the deaths of these plants under field conditions.

Exposing the illegal trade in Encephalartos species at the Faraday ‘muthi’ market in South Africa using DNA barcoding

Exposing the illegal trade in Encephalartos species at the Faraday ‘muthi’ market in South Africa using DNA barcoding

Exposing the illegal trade in Encephalartos species at the Faraday and Durban ‘muthi’ markets in South Africa using DNA barcoding

Exposing the illegal trade in Encephalartos species at the Faraday and Durban ‘muthi’ markets in South Africa using DNA barcoding

Diseases and pests of Encephalartos species in South Africa

Diseases and pests of Encephalartos species in South Africa

South African Cycads at Risk:Aulacaspis yasumatsui(Hemiptera: Coccoidea: Diaspididae) in South Africa

The scale insect Aulacaspis yasumatsui is native to Southeast Asia and a major pest of cycad (Cycadales) plants. Due to an increase in worldwide trading of cycads, A. yasumatsui has spread globally and has become a major threat to many cultivated and native cycads worldwide. In this study we report formally, for the first time, A. yasumatsui infesting cycads in South Africa. This scale insect was observed infesting cycads in three provinces in South Africa, namely, Gauteng, KwaZulu-Natal and Limpopo. Its identification was based on morphology and nucleotide sequences of three gene regions. Although more common and damaging on non-native Cycas species, its presence on some native South African Encephalartos species is of concern and effort should be made to control the spread and impact of this pest in the country.

From fragments to figures: Estimating the number of Encephalartos stems in a muthi market

There is an active trade in South African Encephalartos species in traditional medicine (muthi) outlets throughout the country. No attempt has been made to date to estimate the number of individual stems damaged by harvesters supplying stem fragments (including bark strips) to the markets. To progress from stem fragments to stem figures, a plausible technique of enumerating the number of stems from which the fragments were derived is proposed. The method considered the physical condition, post-harvest age and stem diameter of fragments identified to species level. From the samples of 133 cycad fragments purchased in the Johannesburg and Durban muthi markets in 2009, it was estimated that they originated from 81 different damaged stems (66% of which were likely to have been from Encephalartos natalensis). This estimate is a significant advance in quantifying this hitherto unknown aspect of the cycad trade.

Sifting through cycads: A guide to identifying the stem fragments of six South African medicinal Encephalartos species

Sixty-three percent of the world's cycad taxa are threatened with extinction. In South Africa, 25 of the 38 indigenous species are categorised as Threatened on the IUCN Red List, primarily due to illegal collecting. Three of the country's Encephalartos species are already Extinct in the Wild, while 10 Critically Endangered endemic Encephalartos species are undergoing rapid local extirpations across their ranges. Nearly two-thirds of South Africa's Encephalartos species are used for traditional medicine, some of which are sold in traditional medicine markets in the form of bark strips and stem fragments. The leafless Encephalartos stems encountered in the medicinal and horticultural trades are generally difficult to identify to species and, since species identification of South African Encephalartos using DNA barcoding is not yet feasible, alternative methods of identification are required. To determine the identity of the species sold in South Africa's two largest traditional medicine markets in KwaZulu-Natal (KZN) and Gauteng, surveys were conducted in the Warwick and Faraday markets respectively. Stem fragment samples purchased from the vendors in the markets were identified to species using stem and leaf base morphological characters in tandem with harvesting locality records. Six KZN Encephalartos species were successfully identified viz. E. ferox, E. ghellinckii, E. natalensis, E. ngoynaus, E. senticusos and E. villosus. Photographs of stem fragments and leaf bases of each species are presented here with supplementary quantitative and descriptive stem anatomical data. This paper therefore presents an identification guide to assist researchers and law enforcement officers in the identification of Encephalartos species unlawfully harvested for the traditional medicine and horticultural trades. The guide is thus also useful in the emerging discipline of wildlife forensics, and offers a unique approach to determining difficult-to-identify Encephalartos stem material.

Variation in the chemical composition of cone volatiles within the African cycad genus Encephalartos

Volatiles play a key role in attraction of pollinators to cycad cones, but the extent to which volatile chemistry varies among cycad species is still poorly documented. Volatile composition of male and female cones of nineteen African cycad species (Encephalartos; Zamiaceae) was analysed using headspace technique and gas chromatography–mass spectrometry (GC–MS). A total of 152 compounds were identified among the species included in this study, the most common of which were monoterpenes, nitrogen-containing compounds and unsaturated hydrocarbons. Male and female cones emitted similar volatile compounds which varied in relative amounts with two unsaturated hydrocarbons (3E)-1,3-octadiene and (3E,5Z)-1,3,5-octatriene present in the volatile profile of most species. In a multivariate analysis of volatile profiles using non-metric multidimensional scaling (NMDS), a number of species clusters were identified according to shared emission of unsaturated hydrocarbons, pyrazines, benzenoids, aldehydes, alkanes and terpenoids. In comparison, terpenoids are common in Zamia and dominant in Macrozamia species (both in the family Zamiaceae) while benzenoids, esters, and alcohols are dominant in Cycas (Cycadaceae) and in Stangeria (Stangeriaceae). It is likely that volatile variation among Encephalartos species reflects both phylogeny and adaptations to specific beetle pollinators.

Cycad collicles (“leaflet nodules”)

The presence of small knobs/nodules found on the adaxial leaflet surface of some Encephalartos species was investigated in 134 cycad species of nine genera. The knobs, referred to as collicles, were found to be the result of connecting mucilage canal ‘bridges’ over vascular bundles, connecting mucilage canals situated between adjacent parallel vascular bundles. Collicles were found on some Encephalartos species only and not always on all individuals of the same species. The possible taxonomic value of these collicles is discussed.

Quantifying the Trade in Cycads (Encephalartos Species) in the Traditional Medicine Markets of Johannesburg and Durban, South Africa1

Quantifying the Trade in Cycads ( Encephalartos Species) in the Traditional Medicine Markets of Johannesburg and Durban, South Africa. Cycads have been used for traditional purposes for centuries, mainly as a source of starch during droughts and famines. In South Africa, Encephalartos species are traded for traditional medicine (TM) in local TM markets. The 2009 IUCN Red Data assessment for South African flora lists 78% of the 37 indigenous Encephalartos species as “Threatened”, with three species already “Extinct in the Wild” (EW). South African cycads face an extinction crisis, primarily due to collecting for the horticultural trade. The trade in Encephalartos for TM also has a significant impact on several species, and is largely understudied. In this paper, the trade in Encephalartos for TM was quantified in South Africa’s two largest TM markets, Faraday in Johannesburg and Warwick in Durban. Harvesting of South African Encephalartos for TM involves the removal of bark strips and/or whole stem sections. Encephalartos species were sold at 26% and 13% of the stalls at Faraday and Warwick, respectively, with an estimated 9.0 metric tons traded at Warwick in 2009. Stem samples purchased in the markets were assigned to stem diameter size classes using a size class chart, and regression analysis was used to validate the allocations. Most harvesting was from sub-adult and adult cycads, and it appears that bark strips are removed from large arborescent plants, whereas smaller individuals and subterranean-stemmed species are harvested by removing the entire plant. There is generally a positive relationship between stem diameter and leaf base length as well as stem diameter and pith radius. The former can be used as a predictor of stem diameter size class for market samples that prove difficult to assign to diameter classes using the chart. Overall, this is the first study to quantify the trade in Encephalartos for TM in South Africa with reference to the size classes of the plants traded.

Uncovering the cycad taxa ( Encephalartos species) traded for traditional medicine in Johannesburg and Durban, South Africa

The bark and stems of Encephalartos species are used for traditional medicine across South Africa, and some species are traded in traditional medicine markets. The absence of characteristic plant parts such as leaves and cones in the chopped up market material presents a major challenge to the identification of the species traded. In this study, South Africa's two largest traditional medicine markets, Faraday in Johannesburg and Warwick in Durban, were surveyed to ascertain the source areas and species of Encephalartos in trade. Samples of stem fragments were purchased from vendors, identified to probable species and their stem diameter size class distributions determined using a specially designed size class chart. Species identification was undertaken by comparing trader citations of harvesting areas with the distributions of Encephalartos species in the province of KwaZulu-Natal (since all the specimens originated from KZN). The species most commonly recorded in the markets were identified as Encephalartos natalensis, E. villosus and E. ghellinckii; small quantities of what are likely to be E. ferox and E. senticosus were also observed. Following this study, the total number of South Africa's 37 Encephalartos species recorded as being used for traditional medicine is 25. Stem diameter size class distributions showed that most stem fragments came from sub-adult and adult cycads. Large arborescent species appear to be harvested by removing bark strips from adult individuals, while smaller arborescent and subterranean species are harvested by removing the entire plant. Regression relationships between stem tissue type and stem diameter for E. natalensis and E. ghellinckii indicate a strong, positive linear relationship of leaf base length and pith radius with stem diameter. Overall, this is the first known study that attempts to identify the cycad species traded in South African traditional medicine markets in conjunction with the size classes of the specimens in trade.

Molecular systematics and evolution in an African cycad-weevil interaction: Amorphocerini (Coleoptera: Curculionidae: Molytinae) weevils on Encephalartos

Weevils in the tribe Amorphocerini have been implicated in pollination of Encephalartos species in southern Africa. The services they render these plants and the unique attributes of the cycad-weevil interaction make them important from both conservation and evolutionary standpoints. Oberprieler [Oberprieler, R.G., 1996. Systematics and evolution of the tribe Amorphocerini, with a review of the cycad weevils of the world. Ph.D. dissertation, University of the Free State, Bloemfontein, South Africa], using morphological characters, proposed a tentative hypothesis of relationships among the Amorphocerini which is tested here using DNA sequence data. Sequences from one mitochondrial and three nuclear genes were used to infer phylogenetic relationships, levels of sequence divergence, evolution of host associations, and patterns of speciation in this tribe. The results are reasonably consistent with the morphological hypothesis of relationships and species concepts, though important differences are observed, particularly in relationships among a Porthetes hispidus Boheman species group, which is indicated to have experienced recent divergences. In general, low levels of sequence divergence among species within two of the three genera indicate a recent radiation of this tribe onto African cycads, thus while cycad–insect interactions have often been considered ancient this may not be the case for some extant interactions. A complex pattern of host shifts onto both closely related and more distantly related hosts is suggested.

Post-shedding seed behaviour of selected Encephalartos species

Post-shedding seed behaviour of selected Encephalartos species

Azoxyglycoside content and β-glycosidase activities in leaves of various cycads

Azoxyglycoside contents in leaves of 32 cycad species belonging to 10 cycad genera and the seeds of 4 Encephalartos species were analyzed by HPLC with a YMC-PA03 amide column. Azoxyglycosides were detected in mature leaves of 14 cycad species including 2 Bowenia, 2 Lepidozamia, 1 Microcycas, and 1 Stangeria species, but not in mature leaves of 18 other cycad species; 2 of 3 Ceratozamia, 1 of 3 Cycas, 3 of 3 Dioon, 10 of 11 Encephalartos, 1 of 3 Macrozamia and 1 of 3 Zamia species analyzed. The ratios of β-glycosidase activity toward cycasin and macrozamin in extracts from the leaves of 9 species belonging to 9 genera were measured. The hydrolysis of cycasin was higher in the leaf extracts of Cycas revoluta, Bowenia spectabilis, Stangeria eriopus and Ceratozamia mexicana, whereas in Lepidozamia hopei, the hydrolysis levels of cycasin and macrozamin were similar. On the other hand, activity toward macrozamin was higher in Dioon edule, Encephalartos villosus, Macrozamia miquelii and Zamia fischeri. The hydrolytic activities in most species were estimated to be sufficient for the release of methylazoxymethanol in leaves analogous to the cyanogenesis of cyanogenic plants. Therefore, hydrolysis of azoxyglycosides by endogenous glycosidase in leaves seems to occur by accidental injury of leaves. However, in M. miquelii leaf extract, hydrolytic activity toward macrozamin was high and the activity toward cycasin was very low, though only cycasin was found in the leaves of this species.

The longevity of cycad pollen in storage

An investigation was made into the effects of temperature, headspace atmosphere and humidity on the longevity of stored pollen from several Encephalartos species and from Cycas thouarsii. Samples were assayed by in vitro germination tests and by in vivo pollination trials. Encephalartos pollen rapidly lost germinability at ambient temperatures but retained 50% germinability for approximately two years at 0°C and three years at − 15°C. Storage in ambient atmosphere resulted in better germinability than storage in a nitrogen atmosphere. Pre-drying for 24 h was beneficial but storage over a desiccant was disadvantageous. Pollen stored for 2 years at 0 – 4°C gave rise to a 58% seed germination when used to pollinate a female Encephalartos transvenosus cone. Pollen of Cycas thouarsii stored at reduced temperatures exhibited a pronounced seasonal variation in germinability with reduction in maxima over a 3-year period, implying the operation of a hitherto undocumented biological clock.

Disintegration of Encephalartos megastrobili

The female cones (megastrobili) of most Encephalartos species, notably E. altensteinii Lehm. and E. lebomboensis Verdoorn which were used in this study, disintegrate basipetally. Initially a decrease in the water potential of the seeds results in transfer of water from the megasporophylls to the seeds. The resulting expansion of the seeds causes an increase in the diameter of the periferal seed band which sets up a tension in the sporophyll stalks. This tension induces the autolysis of a narrow cross-sectional band of tissue in the basal part of the sporophyll stalk, followed by the rupture of the sporophyll from the cone axis at this point. The enlargement of the seeds also forces the apical seed-bearing sporophylls to slide over the sterile sporophylls at the cone apex. The subsequent dehydration of the sporophylls and simultaneous abscission of the seeds is followed much later by the abscission of the cone axis from the plant’s stem to complete the disintegration process.