A Cladistic Analysis of the Subtribe Sicyinae (Cucurbitaceae)

Abstract

The subtribe Sicyinae includes six genera (Microsechiutn, Parasicyos, Sechiopsis, Sechiumn, Sicyos, and Sicyosperma). In this paper, monophyly of this subtribe and phylogenetic relationships among its genera are explored by means of a cladistic analysis. Twenty nine morphological and palynological characters, and 22 taxa representative of all genera of subtribe Sicyinae were included in the analysis. The taxa used as outgroup were the genera Cyclanthera and Echinopepon, two members of the subtribe Cyclantherinae, the sister group of Sicyinae according to the current classification of the family Cucurbitaceae. Two equally most parsimonious cladograms (L = 78, CI = 0.615, RI = 0.764, HI = 0.564) were obtained. In both cladograms, the members of the subtribe Sicyinae were clustered as a monophyletic group. However, the monophyly of Microsechiuni, Parasicyos and Sicyos was not clearly supported, and their relationships could not be defined. In contrast, Sechiopsis and Sechium formed a monophyletic group supported by the presence of defined floral nectaries at the base of the receptacle. The results confirm the strong relationships between these two genera suggested in previous papers. However, while the monophyly of Sechiopsis was clearly supported by the presence of winged fruits, no synapomorphy was found either for the whole genus Sechium or for its two currently accepted sections. Nevertheless, the results also revealed that there is not any evidence to place the members of Sechium in three different genera (Sechium, Frantzia and Polakowskia) as has been proposed by other authors.