HALL, JOCELYN C.* and KENNETH J. SYTSMA. University of Wisconsin, Madison, WI, USA. - A new placement of members of tribe Stixeae (Capparaceae) based on DNA sequences.
Variation in habit and a bewildering array of floral and fruit forms
has likely contributed to making Capparaceae a ‘trash basket’ family.
Recent phylogenetic analyses based on chloroplast sequence data
indicate Capparaceae are paraphyletic with the monophyletic subfamily
Cleomoideae more closely related to Brassicaceae then to subfamily
Capparoideae (Capparaceae). Capparoideae also form a monophyletic
clade with the exclusion of an anomalous genus, Forchhammeria.
Although this genus is clearly placed outside the Capparaceae and
Brassicaceae lineage, the precise relationship of Forchhammeria
among other core Brassicales is unresolved. Forchhammeria (ten
species) is endemic to the New World and has been placed in the tribe
Stixeae along with Asiatic genera Stixis (seven species),
Tirania (one species), and Neothorelia (one species)
based on the floral characteristic of the unusual merosity number of
six for Capparaceae (typically tetramerous). The goal of this study
was to clarify the placement of the tribe Stixeae, especially the
genus Forchhammeria, within the core Brassicales by using
evidence from DNA sequences of rbcL, ndhF,
trnL-trnF and matK. We were able to get DNA materials of
almost all species of Forchhammeria and the genus
Tirania. We sampled broadly within Capparaceae, Cleomaceae, and
Brassicaceae as well as closely related families including
Gyrostemonaceae, Resedaceae, Pentadiplandraceae, and Tovariaceae.
These data indicate Tirania and Forchhammeria are most
closely related to Gyrostemonaceae and Resedaceae. The phylogeny is
used to assess floral character evolution as well as the evolution of
dioecy among the core Brassicales.
Key words: Brassicales, Capparaceae, chloroplast DNA, Forchhammeria, phylogenetics