Phylogenomic insights into Neotropical Magnolia relationships

Abstract

Despite extensive research into the phylogenetic relationships of the genus Magnolia, Neotropical taxa have been neglected. This is partly because their numbers have recently doubled and now account for almost half of the global richness. Therefore, by sampling one-third of all Neotropical taxa their relationships were studied using morphological, nuclear, and plastome data. Two major clades were identified: Clade I, comprising Magnolia sect. Talauma, Magnolia sect. Splendentes from the Neotropics, and the Asian Magnolia sect. Gwillimia; while Clade II included the Neotropical clades Magnolia sect. Macrophylla and Magnolia sect. Magnolia, along with the remaining non-Neotropical sections. Within Clade I, Magnolia sect. Talauma was geographically divided into a northern subclade grouping Mexican and Central American taxa, and a southern subclade comprising South American and Caribbean taxa. Magnolia sect. Splendentes was also dichotomously divided, corresponding to the former Magnolia sect. Talauma subsect. Cubenses and Magnolia sect. Talauma subsect. Dugandiodendron. In Clade II, the relationships within Magnolia sect. Macrophylla and Magnolia sect. Magnolia were unclear, suggesting a species complex in all Magnolia sect. Macrophylla taxa. In total, 25 morphological traits were assessed, and ancestral state reconstructions were carried out. Only the joined clustering of mature follicles was a synapomorphy for the southern subclade of Magnolia sect. Talauma. In conclusion, this highlights the need to re-assess the taxonomic delimitation of certain groups, to update the infrageneric classification of Neotropical clades and to explore morphological traits to support them.

Keywords: Infrageneric classification; Macrophylla; Magnoliaceae; Plastome; Splendentes; Talauma.

Fig. 1

Magnolia clades of Neotropical distribution. A: Magnolia sect. Talauma subsect. Cubenses. B. Magnolia sect. Talauma subsect. Dugandiodendron. C. Magnolia sect. Macrophylla. D. Magnolia sect. Magnolia. E. Magnolia sect. Talauma subsect. Talauma.

Fig. 2

Plastid and nuclear data phylogenetic topologies obtained from Bayesian Inference and comparison among them in tanglegram. Values on nodes represent Posterior Probabilities (PP).

Fig. 3

Multispecies coalescent tree based on maximum likelihood from 74 nuclear sequences of 53 Magnolia species. Values on nodes represent Bootstrap Percentages (BP).

Fig. 4

Ancestral-state reconstructions for the clustering type of mature follicles based on Bayesian Inference (BI) and maximum likelihood (ML) approaches A. Plastid tree based on BI from 104 sequences of 68 Magnoliaceae taxa. B. Plastid tree based on ML from 104 sequences of 68 Magnoliaceae taxa. C. Nuclear tree based on BI from 74 sequences of 58 Magnoliaceae taxa. D. Nuclear tree based on ML from 74 sequences of 58 Magnoliaceae taxa.

Fig. 5

Ancestral-state reconstructions for the auriculate and cordate leaf base shapes from 104 plastid sequences of 68 Magnoliaceae taxa based on Bayesian inference (BI) and maximum likelihood (ML) approaches: A. Auriculate leaf base shape ancestral estimation tree based on BI; B. Auriculate leaf base shape ancestral estimation tree based on ML; C. Cordate leaf base shape ancestral estimation tree based on BI; D. Cordate leaf base shape ancestral estimation tree based on ML.