Dalbergioid sensu lato clade

Introduction

The "Dalbergioid sens. lat." clade includes the tribe Amorpheae and the "dalbergioid sens. str." clade ("dalbergioids" sensu Lavin et al., 2001). First described by Lavin et al. (2001), the "dalbergioid" legumes are a pantropical group of papilionoids originally recognized on the basis of combined molecular and morphological phylogenetic evidence and circumscribed to include all genera (44 genera, c. 1100 species) previously referred to the tribes Aeschynomeneae, Adesmieae, subtribe Bryinae of the Desmodieae, and tribe Dalbergieae except for Andira, Hymenolobium, Vatairea, and Vataireopsis (Lavin et al., 2001). The discovery of the dalbergioid clade prompted a re-examination of root nodule structure within this group and the subsequent conclusion that the "aeschynomenoid" type of root nodule (Sprent, 2001) is a non-molecular synapomorphy for this clade (Lavin et al., 2001). The tribe Amorpheae consists of eight genera (c. 240 species), all American, of small trees and perennial and annual herbs distributed primarily in warm temperate and desert regions of the northern hemisphere, but most abundant and diverse in Mexico (Barneby, 1977).

Discussion of Phylogenetic Relationships

The recognition of the dalbergioid legumes by Lavin et al. (2001) brought together members of tribes Aeschynomeneae, Adesmieae, Dalbergieae, and subtribe Bryinae of the Desmodieae, but the position of this clade within Papilionoideae was not well clarified by their analysis; preliminary evidence suggested that its sister group included the tribe Amorpheae. More recent studies based on analyses of molecular sequence data (McMahon and Hufford, 2004; Wojciechowski et al., 2004) provide convincing support for the monophyly of Amorpheae, confirming Barneby's (1977) hypothesis of Amorpheae as a 'natural group', and place Amorpheae as the sister group to the dalbergioids sensu Lavin et al. (2001). Together these two clades comprise what has been referred to as the "dalbergioids sens. lat." clade (Wojciechowski et al., 2004). Similarities in base chromosome number, the presence of glandular punctuate leaves, and indehiscent single-seeded pods among many dalbergioids also support this relationship with Amorpheae (Wojciechowski et al., 2004). Furthermore, these studies suggest weak support for a sister group relationship of the primarily tropical American genera Andira and Hymenolobium of Dalbergieae to the dalbergioids sens. lat. clade.

Within dalbergioids, three informal, well-supported subclades are recognized (Lavin et al., 2001): the Adesmia clade (6 genera, c. 360 species mainly Neotropical), the Dalbergia clade (17 genera, c. 706 species pantropical, centered in Africa), and the Pterocarpus clade (22 genera, c. 200 species mainly Neotropical). In the analysis of Amorpheae by McMahon and Hufford (2004), two well-supported subclades were recognized: the "Amorphoid" clade (Amorpha, Apoplanesia, Errazurizia, Eysenhardtia, and Parryella), characterized by non-papilionaceous flowers, and the "Daleoid" clade (Dalea, Marina, and Psorothamnus), characterized by generally papilionaceous corollas.

References

Barneby, R. C. 1977. Daleae Imagines, An illustrated revision of Errazurizia Philippi, Psorothamnus Rydberg, Marina Liebmann, and Dalea Lucanus emend. Barneby, including all species of Leguminosae of tribe Amorpheae Borissova ever referred to Dalea. Memoirs of the New York Botanical Garden 27: 1-892.

Lavin, M., R. T. Pennington, B. B. Klitgaard, J. I. Sprent, H. C. de Lima, and P. E. Gasson. 2001. The dalbergioid legumes (Fabaceae): delimination of a pantropical monophyletic clade. American J. Botany 88: 503-533.

McMahon, M., and L. Hufford. 2004. Phylogeny of Amorpheae (Fabaceae: Papilionoideae). American J. Botany 91: 1219-1230.

Wojciechowski, M. F., M. Lavin, and M. J. Sanderson. 2004. A phylogeny of legumes (Leguminosae) based on analysis of the plastid matK gene resolves many well-supported subclades within the family. American J. Botany 91: 1846-1862.