Insights on the evolutionary origin of Detarioideae, a clade of ecologically dominant tropical African trees

Abstract

African tropical forests are generally considered less diverse than their Neotropical and Asian counterparts. By contrast, the Detarioideae is much more diverse in Africa than in South America and Asia. To better understand the evolution of this contrasting diversity pattern, we investigated the biogeographical and ecological origin of this subfamily, testing whether they originated in dry biomes surrounding the Tethys Seaway as currently hypothesized for many groups of Leguminosae. We constructed the largest time-calibrated phylogeny for the subfamily to date, reconstructed ancestral states for geography and biome/habitat, estimated diversification and extinction rates, and evaluated biome/habitat and geographic shifts in Detarioideae. The ancestral habitat of Detarioideae is postulated to be a primary forest (terra firme) originated in Africa-South America, in the early Palaeocene, after which several biome/habitat and geographic shifts occurred. The origin of Detarioideae is older than previous estimates, which postulated a dry (succulent) biome origin according to the Tethys Seaway hypothesis, and instead we reveal a post Gondwana and terra firme origin for this early branching clade of legumes. Detarioideae include some of the most dominant trees in evergreen forests and have likely played a pivotal role in shaping continental African forest diversity.

A new phylogeny-based tribal classification of subfamily Detarioideae, an early branching clade of florally diverse tropical arborescent legumes

“…The two species also share a deep hypanthium 4,80–82 . Although it is possible to argue that these three genera should be included in a single tribe Schotieae, the phylogenetic pattern obtained here and in previous studies 29–31,43 do not allow us to unequivocally conclude that Schotia forms a monophyletic group with Goniorrhachis and Barnebydendron . This approach with increased division at the tribal level provides a stricter phylogenetic framework for testing evolutionary hypotheses because we do not assume that the two lineages, which morphologically are also very distinct, are necessarily sister clades.

Figure 5Detarioideae photographs.

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“…Three genera, Schotia , Goniorrhachis and Barnebydendron , always appear among the early branching clades within Detarioideae 29–31,43 , and in our analyses these are resolved as sister to the resin-producing Detarioideae, although this relationship is weakly supported (Figs 2, 5). Schotia (four species) has been consistently resolved as monophyletic in all analyses (Fig.…”

“…We re-circumscribed tribe Detarieae (Figs 2, 5) as equivalent to the resin-producing clade of previous phylogenetic studies 30,36,43 . This clade was named subtribe Detariinae by Fougère-Danezan et al .…”

“…Detarioideae represent an early branching lineage within Leguminosae evolution, estimated at 68–63 Ma 43 , and comprising six strongly supported main clades. These six clades have also been resolved in previous studies; and here we recognize them at the tribe level: Schotieae Estrella, L.P. Queiroz & Bruneau, Barnebydendreae Estrella, L.P. Queiroz & Bruneau, Detarieae DC., Saraceae Estrella, L.P. Queiroz & Bruneau, Afzelieae Estrella, L.P. Queiroz & Bruneau, and Amherstieae Benth.…”

“…More recently Estrella et al . 43 studied the biogeographic origin of the subfamily proposing a probable terra firme African origin in the Palaeocene with subsequent and frequent early dispersals to South America and Asia.…”