Molecular systematics of Iridaceae: Evidence from four plastid DNA regions

Iridaceae are one of the largest families of Lilianae and probably also amo ng the best studied of monocotyledons. To further evaluate generic, tribal, and subfamilial relationships we have produced four plastid DNA data sets for 57 genera of Iridaceae plus outgroups: rsp4, rbcL (both protein-coding genes), the trnL intron, and the trnL-F intergenic spacer. All four matrice s produce similar although not identical trees, and we thus analyzed them i n a combined analysis, which produced a highly resolved and well-supported topology, in spite of the fact that the partition homogeneity test indicate d strong incongruence. In each of the individual trees, some genera or grou ps of genera are misplaced relative to morphological cladistic studies, but the combined analysis produced a pattern much more similar to these previo us ideas of relationships. In the combined tree, all subfamilies were resol ved as monophyletic, except Nivenioideae that formed a grade in which Ixioi deae were embedded. Achlorophyllous Geosiris (sometimes referred to Geosiri daceae or Burmanniaceae) fell within the nivenioid grade. Most of the tribe s were monophyletic, and Isophysis (Tasmanian) was sister to the rest of th e family; Diplarrhena (Australian) fell in a well-supported position a, sis ter to Irideae/Sisyrinchieae/Tigridieae/Mariceae (i.e., Iridoideae); Bobart ia of Sisyrinchieae is supported as a member of Irideae. The paraphyly of N ivenioideae is Suspicious due to extremely high levels of sequence divergen ce, and when they were constrained to be monophyletic the resulting trees w ere only slightly less parsimonious (<1.0%). However, this subfamily also l acks clear morphological synapomorphies and is highly heterogeneous, so it is difficult to develop a strong case on nonmolecular grounds for their mon ophyly.