Taxonomic Revision of the Alectra sessiliflora Complex (Orobanchaceae)

Alectra sessiliflora (Orobanchaceae) is the most widespread species within the genus, occurring throughout sub-Saharan Africa, and into India, China and the Philippines. Three varieties are currently recognized (A. sessiliflora var. monticola, A. sessiliflora var. senegalensis, and A. sessiliflora var. sessiliflora) and are distinguished by geographic range, calyx pubescence and stamen filament pubescence. Due to the overlapping nature of the characters used to distinguish among these varieties, accurate assignment of a specimen to a single variety is nearly impossible. We undertook a phenetic study of morphological characters to assess the validity of these varieties. Principal coordinate analysis and the unweighted pair-group method using arithmetic averages were used to explore whether specimens would cluster into the currently recognized varieties. Our analyses revealed no clustering based exclusively on geographic distribution. A small cluster of seven specimens was seen in the principal coordinate analysis using Gower's coefficient of similarity as input values, but this cluster was not diagnosable by unique characters. Based on these results we recommend that Alectra sessiliflora be recognized without infraspecific taxa. Finally, additional names are included as synonyms under Alectra sessiliflora based on extensive study of field-collected and herbarium specimens.