Morphological and habitat differentiation between diploids and tetraploids of a Drakensberg near-endemic taxon, Rhodohypoxis baurii var. platypetala (Hypoxidaceae)

Environmental factors may shape the spatial distribution of ploidy levels. Here, we undertook a cytogeographical study of Rhodohypoxis baurii var. platypetala (Hypoxidaceae), a Drakensberg near-endemic taxon. We addressed the following questions: (1) Are there mixed-ploidy populations or is each population represented by a single ploidy level? (2) Is there a pattern in the environmental distribution of ploidy levels? (3) Are there specific environmental variables associated with each ploidy level locality? (4) Are plant traits similar or different within and among ploidy levels across populations that experience different environmental factors? We measured leaf and flower traits of individuals that were sampled for flow cytometry from 17 populations across the KwaZulu-Natal and Free State provinces in South Africa. We extracted daily climate data for 13 variables and collected soil samples to evaluate pH and nutrient properties to characterize the sampled populations to test for relationships with ploidy level distributions. Twelve populations were found to contain only diploids, four populations contained only tetraploids, and only one population was ‘mixed ploidy’ (both diploid and triploid individuals present). There was an overlap in the altitudinal range of diploid and tetraploid populations, but diploids reached the highest altitudes recorded for the current study. We also found that R. baurii var. platypetala occurs in acidic soils and that tetraploids occurred in soils with marginally higher nitrogen and phosphorus than soils where diploids occur. Tetraploids generally occurred in warmer conditions, in drier soils, and possessed broader leaves and larger flowers than diploids. Our study suggests that soil factors and temperature at a small (within localities) spatial scale likely shape ploidy level distributions in the Drakensberg grasslands.