Abstract
Background: The species-rich flora of southern Africa comprises a high number of endemics, including succulents such as the flowering stones in the genus Lithops, but conservation status for these species is not well underpinned because detailed field data and assessments of genetic diversity are lacking.Objectives: We wanted to assess plant abundance and identify factors that may affect survival in Lithops ruschiorum through carefully conducted field surveys, and to determine amount and partitioning of genetic variation by amplified fragment length polymorphism (AFLP) analysis.Method: Field surveys were carried out in nine populations in Namibia. The most meticulously studied population was divided into 51 sites, while another 43 sites were recognised in the remaining eight populations. At each site, occupied area and number of plants were recorded as well as altitude, aspect, slope, soil texture and substrate. Amplified fragment length polymorphism markers were employed to study 52 individuals from seven populations.Results: In total, 8465 individuals were recorded. Plant density and/or plant number was associated with aspect, slope, soil texture, substrate and geographic distance from the coast. Analysis of molecular variation showed that 95% of the variability occurs within populations. Genetic and geographic distances among populations were correlated suggesting an isolation-by-distance pattern.Conclusion: Results are concordant with a strong impact of fog-based precipitation on plant density in the coastal populations, whereas rain probably is more important at one population which is situated further inland. Within-population genetic variation was medium high as usually reported for perennial, outcrossing species, but the low population differentiation implies considerable gene flow and/or population fragmentation.
Highlights
Southern Africa harbours many endemic leaf succulents because of the unique environmental conditions (Young & Desmet 2016), but few of these taxa have been thoroughly studied in spite of imminent threats due to climate change and human activities such as illegal collecting of seeds and live plants, and habitat destruction resulting from prospecting, mining, off-road driving and, in recent years, the production of motion pictures in different parts of the Namib desert (Jainta 2017; Loots 2005, 2011)
We focus on L. ruschiorum (Dinter & Schwantes) N.E.Br., which is endemic to Namibia and distinguishable from other Lithops species by its highly cordate profile, leaves that are often elevated above the soil surface and the very smooth, pale white to greyish or buff-coloured leaf face with few markings (Figure 1)
Lithops ruschiorum grows in the central and northern desert biome of Namibia (Irish 1994), and has a distribution area that stretches more than 600 kilomtres along the coast and approximately 75 km inland (Cole & Cole 2005)
Summary
Southern Africa harbours many endemic leaf succulents because of the unique environmental conditions (Young & Desmet 2016), but few of these taxa have been thoroughly studied in spite of imminent threats due to climate change and human activities such as illegal collecting of seeds and live plants, and habitat destruction resulting from prospecting, mining, off-road driving and, in recent years, the production of motion pictures in different parts of the Namib desert (Jainta 2017; Loots 2005, 2011). The species-rich flora of southern Africa comprises a high number of endemics, including succulents such as the flowering stones in the genus Lithops, but conservation status for these species is not well underpinned because detailed field data and assessments of genetic diversity are lacking
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