Evolution and Development in the Amorphoid Clade (Amorpheae: Papilionoideae: Leguminosae): Petal Loss and Dedifferentiation

Abstract

We used comparative developmental morphology to study the evolution of nonpapilionaceous corollas in the amorphoid clade of the tribe Amorpheae (Papilionoideae). This clade consists of five genera in which there are no papilionaceous corollas (five petals differentiated into one banner, two wing, and two keel petals). We studied the ontogenies of three nonpapilionaceous forms: corollas consisting of one petal (exemplified by Amorpha canescens), no petals (Parryella filifolia), and five petals in two types (Errazurizia megacarpa). We compared these to the ontogeny of a papilionaceous corolla (exemplified by the closely related Psorothamnus scoparius). In A. canescens, all petals initiated, but four did not grow beyond the primordial stage. In P. filifolia, no distinct petal primordia were visible. The corolla of E. megacarpa, which has only two types of petals, exhibits nonpapilionaceous characteristics at an early ontogenetic stage. Aside from the earliest primordial mounds, the petals of Psorothamnus and Errazurizia do not resemble each other, indicating that paedomorphosis is not responsible for the nonpapilionaceousness of Errazurizia. Comparing the morphological results to a phylogeny, we infer a single origin of the characteristics that differentiate Errazurizia petals from Psorothamnus petals, and we infer at least two evolutionary events leading to the reduced corolla in Parryella, Amorpha, and Errazurizia rotundata. When considered in the context of the remaining Amorpheae, in which additional floral diversification has occurred, and in the context of the entire papilionoid group, in which floral form is relatively conserved, our results indicate a relaxation of selective or developmental constraint within the clade Amorpheae.

Floral ontogeny in Dipterygeae (Fabaceae) reveals new insights into one of the earliest branching tribes in papilionoid legumes

“…The hypanthium in Dipterygeae is characterized by the direct insertion of the petal claw in the hypanthium margin. A similar condition has been reported for Amorpheae (McMahon & Hufford, , ; McMahon, ). Anatomical comparative studies of the vascularization would be valuable to confirm how the hypanthium is formed in different groups of Fabaceae.…”

“…The short hypanthium is another shared characteristic between members of Dipterygeae. It has been described in some other groups of Papilionoideae, including the tribes Amorpheae (McMahon, ; McMahon & Hufford, ), Loteae (Prenner, ), Dalbergieae (Costa et al ., ; Filardi, Garcia & Carvalho‐Okano, ), Sophoreae (Tucker, , , ; Sartori & Tozzi, ; Filardi et al ., ) and Phaseoleae (Tucker, ) and the Lecointea clade (Mansano et al ., ). In Caesalpinioideae s.l.…”

Towards unlocking the deep nodes of Leguminosae: Floral development and morphology of the enigmatic Duparquetia orchidacea (Leguminosae, Caesalpinioideae)

“…These new insights into legume evolution have to be carefully considered when discussing evolutionary trends in floral morphology and development of Leguminosae. Looking for parallels between subfamilies we can for example see that both, loss and reduction/suppression of organs occurred in caesalpinioids (e.g., Tucker, 1988, 1998, 2000a, 2001b; Marazzi and Endress, 2008) and in papilionoids (e.g., Tucker, 1988, 1990, 2003b; Pennington et al, 2000; Prenner, 2004e; McMahon, 2005; McMahon and Hufford, 2005). The same is true for spiral sepal initiation, which is pronounced in several Caesalpinioideae (Tucker, 2003a) but can also be rudimentary in papilionoids (e.g., Klitgaard, 1999; Prenner, 2004e) and for which we showed some evidence in Duparquetia .…”

Changing views of flower evolution and new questions

“…Endress, 2006 ). However, complexity may also be lost in evolution, as shown in Amorpheae (Leguminosae ), in which the architecture of complex keel fl owers has been lost (McMahon and Huff ord, 2005 ), or in Besseya (Plantaginaceae ), in which the corolla tube disappeared (Huff ord, 1995 ).…”