Exo-morphology of vegetative parts support the combination of Solenostemon rotundifolius (Poir) J. K. Morton with Plectranthus esculentus N. E. Br. Natal (Lamiaceae) with insight into infra-specific variability

Exo-morphological characters of two controversial taxa, Plectranthus esculentus N. E. Br. Natal and Solenostemon rotundifolius (Poir) J. K. Morton were studied using both preserved herbarium specimens and living collections from in situ and ex situ sources. The study aimed at gaining a better understanding of specific relationships between the two species in order to improve their identification and classification. Morphological characters derived from leaf, stem, root and tubers were analyzed numerically, using cluster method. The quantitative characters were mostly continuous rather but not discrete while the qualitative characters revealed multistate nature. The preponderance of intermediate characters coupled with similarity in shared characters are indicative of a weak specific boundary in the circumscription of P. esculentus land races and S. rotundifolius. Cluster analysis revealed a strong overall similarity relationship among the varieties and land races in a range of 56 % (minimum) and 74 % (maximum) with an intermediate of 68 %.The findings in this study are consistent with the current treatment of S. rotundifloius in synonymy with P. esculentus. We propose infraspecific recognition of three varieties in the P. esculentus as follows: variety I (P. esculentus var. “Bebot” and P. esculenstus var. “Longat”), var. II (S. rotundifolius var. alba and S. rotundifolius var. nigra), var. III (P. esculentus var. “Riyom”).