Uncovering the patterns of morphological diversity in clades is essential to evolutionary biology. Among the 12,000 species of subfamily Papilionoideae, pea-like flowers are highly conserved. In the tribe Amorpheae, however, they have been lost and flower forms are highly diverse. To understand the origin of morphological diversity in Amorpheae, we have constructed a phylogenetic hypothesis using DNA sequence data from the chloroplast gene trnK and its intron, including the gene matK. Our data, consistent with our previously reported results, strongly support the monophyly of Amorpheae, as well as several clades within Amorpheae. The genera Psorothamnus, Dalea, and Marina are united by sharing a generally papilionoid form, and are supported as a clade. Within this clade, Dalea and Marina are supported as a clade, nested within a paraphyletic Psorothamnus. This result corresponds to predictions we made in studying an unusual petal-stamen synorganization found in Dalea, Marina, and some Psorothamnus. To further resolve relationships within the large genus Dalea and among the closely related genera Amorpha, Errazurizia, and Eysenhardtia, we have added data from the nulcear ITS region. Our analysis of ITS data produced very little conflict with the matK data. For example, Dalea filiciformis is placed as sister to Marina by both data sets. In addition, for the taxa sampled, ITS data resolve relationships between species groups. For example, ITS data strongly support the traditional subgenera Dalea and Parosela. This is predicted by morphology: flowers in Dalea subgenus Dalea generally have unfused corollas, whereas subgenus Parosela tend to have corollas that include a "keel" (two petals marginally fused) that encloses the reproductive structures. The addition of ITS data to our previously acquired matK data allows us to study Amorpheae floral form evolution in greater detail by providing more resolution than with matK alone.

Key words: Amorpheae, Fabaceae, floral evolution, ITS, matK, phylogeny