CROSS, HUGH B.1,2*, RAFAEL LIRA SAADE3, ISELA RODRIGUEZ AREVALO3, and TIMOTHY J. MOTLEY1. 1Lewis B. and Dorothy Cullman Program for Molecular Systematics Studies, The New York Botanical Garden, Bronx, NY 10458; 2Center for Environmental Research and Conservation, Columbia University, New York, NY 10027; 3Unidad de Biotecnologia y Prototipos, Universidad Nacional Autonoma de Mexico, Campus Iztacala, Av. de los Barrios s/n, Los Reyes Iztacala, Tlanepantla, Edo de Mexico. C.P. 54090. - Molecular phylogenetics of the tribe Sicyeae (Cucurbitaceae).
The tribe Sicyeae (Cucurbitaceae) is a large group of vigorously
climbing vines found mostly in the New World tropics, and is composed
of two subtribes, the Sicyinae and Cyclantherinae. The Sicyinae are
characterized by single seeded ovules and include the important
vegetable crop chayote (Sechium edule). Recent morphological
studies have identified major relationships within the tribe. However,
the group has not yet been subjected to molecular analysis. In this
study the phylogenetic relationships of the tribe Sicyeae were
investigated using sequences of the ITS nuclear ribosomal and the
chloroplast trnL-F regions (spacer + intron). All genera in the
tribe were sampled; the genus Cucurbita was used as the
outgroup. Nucleotide sequences of each region were analyzed
independently and in combination using parsimony. Sequence data from
the ITS region were informative at the species level, and could
distinguish between wild and domesticated Sechium edule. The
trnL-F sequence data was informative principally at the generic
level. Rytidostylis, and Cyclanthera were found to be
monophyletic genera. The genera Sicyos and Sechium
appear to be paraphyletic. Additionally, sectional relationships
within Sechium do not seem to conform to earlier hypotheses
based solely on morphology. Within Sechium, the Central
American species form a well-defined monophyletic clade, and include
members of both sections Sechium and Frantzia. The
single species of section Frantzia in Mexico, Sechium
mexicanum, appears to be more closely related to the genera
Sicyos and Sechiopsis.
Key words: chayote, Cucurbitaceae, Sicyeae, systematics