CORTES, ROCIO1*, PIERO G. DELPRETE1, and TIMOTHY J. MOTLEY2. 1Institute of Systematic Botany, The New York Botanical Garden, Bronx NY 10458; 2The Lewis B. & Dorothy Cullman Program for Molecular Systematics Studies, The New York Botanical Garden, Bronx NY 10458. - Systematics of Retiniphyllum (Rubiaceae).
The neotropical genus Retiniphyllum consists of approximately 23
species of shrubs and small trees, most of them occurring in the
Guayana region, and with a few species reaching the Amazon basin,
Central, and Eastern Brazil. This genus is characterized by having
stipules producing copious resinous secretion, inflorescences
racemose, spicate or fasciculate, flowers subtended by bracteoles and
involucels, corollas white, pink or red, anthers with apical and basal
appendages and 5-locular ovary with two collateral ovules per locule.
Because of its peculiar morphological features, the taxonomic position
of Retiniphyllum has been debated among botanists. Robbrecht placed it
in the monotypic tribe Retiniphylleae. Recent phylogenies using
molecular data support Robbrecht's placement in this tribe, and
indicate that this tribe should be included in the Ixoroideae sensu
lato. A phylogenetic analysis using morphological characters was
performed analyzing a data matrix with 23 taxa and 42 characters.
Sipanea and Sipaneopsis were selected as outgroup. The analysis
produced four shortest trees of 169 steps each, where Retiniphyllum
appeared to be monophyletic. The morphological cladogram showed that
white flowers were derived once in Retiniphyllum. A preliminary
phylogenetic analysis using ITS sequences was performed including the
nine Retiniphyllum species of which fresh material was available. In
the phylogeny obtained, two major clades were formed, which seemed to
correspond to Müller's sections Euretiniphyllum (with racemose
inflorescences) and Commianthus (with spicate inflorescences).
According to the results obtained, there was conflict between the
morphological and molecular data. For example, Retiniphyllum
speciosum, a species with red flowers, was nested within the white
flower species in the molecular cladogram. Because the molecular
analyses was performed with only a few species, at this point it is
difficult to determine the significance of the incongruence between
the molecular and morphological phylogenies.
Key words: Guayana Region, ITS, morphology, Retiniphyllum, Rubiaceae, Systematics