MCCAULEY, ROSS A. Department of Environmental and Plant Biology, Ohio University, Athens OH, 45701. - Toward a preliminary phylogeny of the American Gomphrenoideae (Amaranthaceae): Morphology and ITS1 sequences.
The classification of the Amaranthaceae s.s. has divided the family
into two distinct subfamilies, the Amaranthoideae and Gomphrenoideae.
Recent evidence has supported the segregation of a monophyletic
Gomphrenoideae as a group of 20 genera centered in the New World
tropics segregated from the Amaranthoideae principally on the presence
of 1-locular as opposed to the 2-locular anthers in the
Amaranthoideae. Relationships within the subfamily have been
complicated through varying interpretations of floral fusion and a
strong reliance on stigma architecture. To analyze phylogenetic
relationships within the subfamily, a morphological dataset was
constructed using macro- and micromorphological characters for each of
the 20 genera. Parsimony analysis showed that the Gomphrenoideae do
form a monophyletic lineage, and suggested that the group consists of
two principal clades, a Gomphrenoid clade and a Pfaffioid clade.
Further inference into phylogeny was gained through molecular analyses
performed on 27 taxa in 10 of the principal genera of the
Gomphrenoideae using sequences of the internal transcribed spacer 1 of
nuclear ribosomal DNA (nrITS1). Molecular analyses support the
monophyly of the group and provide additional support for two major
clades within the subfamily. Most genera are shown to form
monophyletic lineages, including the large genera Alternanthera
and Iresine. The genus Gomphrena is shown to be
polyphyletic with some species forming a true Gomphrena clade
(G. globosa, G. sonorae, etc.) with the others
distributed within the large Gomphrenoid clade (G. boliviana)
or in close association with the genus Pfaffia (G.
mandonii). The anomalous genus Pseudoplantago is shown to
occur within the Pfaffiod clade of the Gomphrenoideae, despite a
number of morphological characters that have suggested a transfer to
the subfamily Amaranthoideae. The arid North American genus
Tidestromia, exhibiting a unique floral and pollen morphology,
is shown to fall basal to the principal groups of the Gomphrenoideae.
Key words: Amaranthaceae, its1, phylogeny