LI, JIANHUA1,2,3*, JOHN H. ALEXANDER III1, TOM WARD1, PETER DEL TREDICI1, and ROB NICHOLSON4. 1Arnold Arboretum of Harvard University, 125 Arborway, Jamaica Plain, MA 02130; 2Department of Plant Biology, University of New Hampshire, Durham, NH 03824; 3University of Maine, Orono, ME 04469; 4Smith College Botanic Garden, 15 College Lane, Northampton, MA. 01063. - Phylogeny and biogeography of the Empetraceae based on sequences of nuclear and chloroplast genes.
The Empetraceae comprises three genera: Empetrum L.,
Ceratiola Michx., and Corema D. Don. Empetrum has
an antitropical distribution; Ceratiola is endemic to
southeastern US; and Corema is disjunctly distributed in
northeastern North America (C. conradii), Portugal and Spain
(C. album), and the Azores (C. album var.
azoricum). A cladistic analysis of the Empetraceae using 28
morphological characters placed Ceratiola in alternate
positions, with either Empetrum or Corema. This led to
the hypothesis that Ceratiola might be a hybrid between
ancestors of Empetrum and Corema (Anderberg 1994). In
this study we used sequences of nrDNA ITS and chloroplast gene
matK to evaluate the monophyly of Empetrum and
Corema, and to examine phylogenetic relationships of the
Empetraceae. Ten samples were used representing the monotypic
Ceratiola, species and subspecies of Corema, and species
of Empetrum from both Southern and Northern Hemispheres.
Sequences of four species of Rhododendron were withdrawn from
the GenBank and were used as outgroups. In both matK and ITS
trees, species of Empetrum form a clade that is sister to the
strongly supported clade containing both Corema and
Ceratiola, suggesting that Ceratiola may not be of a
hybrid origin between ancestors of Corema and Empetrum.
In the matK tree, Corema conradii is more closely
related to Ceratiola than to Corema album and C.
album var. azoricum, whereas in the ITS tree,
Ceratiola is weakly allied with Corema album and C.
album var. azoricum. This suggests that Ceratiola
might be a hybrid between ancestral populations of Corema
conradii, as a maternal parent, and C. album, as a paternal
parent.
Key words: Ceratiola, Corema, Empetraceae, Empetrum, hybrid, matK, nrDNA ITS, phylogeny