NICKRENT, DANIEL L. 1 AND VALERY MALECOT 2.* 1 Department of Plant Biology and Center for Systematic Biology, Southern Illinois University, Carbondale, IL 62901, USA, 2 Laboratoire de Paléobotanique, Université Pierre et Marie Curie, 12 rue Cuvier, 75005 Paris, France. - Phylogenetic relationships of Santalales based on nuclear small-subunit (18S) rDNA and plastid rbcL with special reference to Olacaceae
As currently classified, Santalales consists of 7 families of
autotrophs, root- and aerial parasites. Within this order, Olacaceae
present both non parasitic and root parasitic members and are thus key
to understanding the origin of the parasitic habit. Sequences of
nuclear ribosomal small subunit rDNA (18S) and chloroplast-encoded
rbcL were used in a combined analysis to study phylogenetic
relationships of the order. The present analysis include 51 genera of
Santalales, 18 of which belong to Olacaceae (from a total of ca. 28
genera). As in previous analyses, Santalales are monophyletic with
Opiliaceae, Loranthaceae and Viscaceae monophyletic and Santalaceae
and Olacaceae paraphyletic. Sampling within Olacaceae is now
sufficiently complete to comment about phylogenetic trends within the
family. Although Schoepfia does not appear to be related to
Olacaceae, its sister relationship with Misodendron received
74% bootstrap support. Moreover, the clade between Schoepfia /
Misodendron and Loranthaceae had a 63% bootstrap value. The
other members of Olacaceae are paraphyletic, and traditional
classifications are only weakly supported. Tribe Couleae forms a
well-supported clade (99% bootstrap). Most of section Anacolosoideae
occurs in a clade (e.g. Strombosia, Strombosiopsis,
Diogoa, Tetrastylidium and Scorodocarpus), except
tribe Anacolosae (Anacolosa and Phanerodiscus in the
present analysis). These latter two genera occur in a clade with
Olax (Olaceae), Ongokea (Aptandrae) and
Chaunochiton (Heisteriae). Malania, considered by
European authors to belong to Olaceae, clearly belong to Ximeniae as
suspected by its Chinese descriptors. Heisteria, the second
member of tribe Heisteriae, does not cluster with Chaunochiton
but occupies a more basal position in the family as does
Erythropalum which has previously been classified in its own
family (Erythropalaceae). Relationships within tribes of Olacaceae
appear to be affected by choice of outgroup taxa. Several of these
relationships are supported by morphological analysis, but further
sampling of the family is needed, particularly for such unusual genera
as Brachynema and Engomegoma.
Key words: Olacaceae,parasitism,phylogeny,Santalales