Biogeography of the Leguminosae
(project completed 2010)
A new semi-arid to arid Tethyan Seaway origin is proposed for the family Leguminosae replacing the traditional wet tropical origin hypothesis.
This project addressed the following questions: 1) What does the evidence of legume distributions and the phylogeny of the family say about a wet versus dry megathermal origin of Leguminosae? 2) Can the crown clade ages of a range of trans-oceanic disjunctions between sister legume taxa inform on whether vicariance (continental history) or dispersal, is largely responsible for the existing pattern of legume distributions?
Four global legume biomes (SUCCULENT, GRASS, RAINFOREST and TEMPERATE) were delimited by Schrire et al. in Biologiske Skrifter 55: 375–422 (2005a) and in Legumes of the World: 21–54 (2005b), which at the broadest level have greatly increased understanding of biogeographical patterns in the Leguminosae. The long-standing West Gondwana ‘equatorial megathermal’ hypothesis for the origin of legumes was rejected for the following reasons. The vicariance analyses of Schrire et al. (2005a) firmly place the semi-arid SUCCULENT biome as the only biome diagnosing the critical nodes of diversification in the legume phylogeny. A dry origin for legumes is in accordance with key morphological synapomorphies and a high nitrogen metabolism in the family. Lineages confined to the SUCCULENT biome gave rise to sublineages occupying all other biomes and the RAINFOREST biome taxa are primarily derived from dry SUCCULENT and GRASS biome taxa. The essentially Tethyan Seaway, SUCCULENT biome (i.e., excluding the extensions into the Southern Hemisphere) largely overlaps with the belt of seasonally dry to arid tropical climate which linked the Caribbean and C America with N Africa (including the Horn) during the Tertiary. This palaeoclimatic belt also coincides with the known spatial and temporal distribution of the oldest legume fossils.
An argument can be supported for vicariance as an explanation for the present disjunct distributions of a number of Palaeocene to Oligocene-aged clade diversifications in legumes, e.g. most tribal and many super-generic-level clades. At the biome (metacommunity)-level, however, the processes of ecological drift, immigration, extinction, and resident speciation have played out over such enormous spatial and temporal scales that any historical signal of the Palaeogene is likely to have been largely swamped if not obliterated altogether. The majority of trans-oceanic crown clades in legumes are Miocene to Holocene in origin, thus much of the present diversity in the family is Neogene in age. This is too recent for disjunctions to be explained by continental history, e.g., large-scale continental movements and land-bridges. The historical legacy of these metacommunities is thus one of dispersal assembly within similar ecological settings world-wide.
The final phase of the project saw a detailed molecular-morphological phylogeny completed for tribe Indigofereae looking at ecological and geographical phylogenetic structure and crown ages of amphi-Atlantic disjunctions in Indigofera, the third largest genus in Leguminosae (see project Systematic study of Tribe Indigofereae). The aim was to do a comprehensive species level analysis that tested the biome hypothesis above, which had been generated originally at family and genus level.
The project was completed in 2010.
Key publications 2005-2010
- Schrire, B.D., Lavin, M. & Lewis, G.P. (2005a). Global distribution patterns of the Leguminosae: insights from recent phylogenies. In Friis, I. & Balslev, H. (eds) Plant diversity and complexity patterns – local, regional and global dimensions. Biologiske Skrifter 55: 375–422.
- Schrire, B., Lewis, G. & Lavin, M. (2005b). Biogeography of the Leguminosae. In G. Lewis, B. Schrire, B., Mackinder. & M. Lock, M. (eds) Legumes of the world. Royal Botanic Gardens, Kew. 21–5.
- Lewis, G.P., Klitgaard, B.B. & Schrire, B.D. (2006). Seasonally dry forests of southern Ecuador in a continental context: insight from legumes. In R.T. Pennington, G.P. Lewis & J.A. Ratter (eds.) Neotropical savannas and seasonally dry forests: plant diversity, biogeography and conservation. Boca Raton: CRC, Taylor & Francis. 281–314.
- Schrire, B.D. (2008). The Madagascan genus Vaughania is reduced to synonymy under Indigofera (Leguminosae-Papilionoideae-Indigofereae). Kew Bulletin 63: 477–479.
- Schrire, B.D., Lavin, M., Barker, N.P. & Forest, F. (2009). Phylogeny of the tribe Indigofereae (Leguminosae–Papilionoideae): Geographically structured more in succulent-rich and temperate settings than in grass-rich environments. American Journal of Botany 96(4): 816–852.
- Callmander, M.W., Labat, J.-N. & Schrire, B.D. (2010). Dealing with Indigofera nivea (Leguminosae) - a new name for Madagascar and a new combination for Africa. In M.W. Callmander, P.B. Phillipson & L.Gautier (eds.) Notes on the flora of Madagascar, 1-5. Candollea 65(2): 363–364.
- Ireland, H.E., Kite, G.C., Veitch, N.C., Chase, M.W., Schrire, B., Lavin, M., Linares, J. & Pennington, R.T. (2010). Biogeographical, ecological, and morphological structure in a phylogenetic analysis of Ateleia (Swartzieae-Fabaceae) derived from combined molecular, morphological and chemical data. Botanical Journal of the Linnean Society 162: 39–53.
Project Partners and Collaborators
M. Lavin, Montana State University, Bozeman