Integrating Quantitative Stem Anatomy and Multivariate Analyses to Resolve Taxonomic Boundaries within the Caralluma Complex (Apocynaceae)
Taxonomic delimitation of the genus Caralluma R.Br. from its segregated genera remains highly problematic due to severe morphological convergence and phenotypic plasticity in their vegetative characters. This study provides a quantitative anatomical characterization of four taxa within the Caralluma segregate complex: Apteranthes tuberculata, Caralluma subulata, Desmidorchis penicillata, and Monolluma quadrangula, to evaluate the systematic utility of the internal stem architecture. The findings revealed that these taxa possess succulent stems partitioned into distinct ribs and sulci, with a single epidermal layer, a specialized cortex, and a central pith. Furthermore, the vascular architecture exhibits a eustelic arrangement, with the internal phloem situated interior to the protoxylem. Quantitative analysis capitalized on these variations and revealed a clear evolutionary trade-off in water-storage strategies: larger, shrubby taxa maximized storage by increasing tissue-layer density, whereas smaller, low-growth taxa relied on cell hypertrophy. Statistical analysis demonstrated that rib cortical layers, pith parenchyma cell areas, and internal phloem distribution were highly significant taxonomic markers. Both cluster analysis (TWCA) and Principal Component Analysis (PCA) successfully resolved the taxa into distinct groups, distinguishing C. subulata as a basal lineage, A. tuberculata as a transitional group, and D. penicillata and M. quadrangula as closely related members of the derived southern clade. Ultimately, these internal structural variations provide a strong anatomical fingerprint for identifying and differentiating these segregated generic lineages.
Department of Biological Sciences
Department of Biological Sciences
Metrics
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
