The Mexican state of Veracruz has suffered very high deforestation rates in the last few decades, and despite the establishment of protected areas and conservation projects, primary forest is now mainly persisting in mostly small, scattered, fragmented remnants. New species of Magnolia section Talauma in this state have been described with little to no reference to the already existing ones, potentially resulting in over-splitting, obscuring their taxonomic delineation and conservation status, and consequently conservation programs. To study the conservation units and their genetic diversity, we here employ 15 microsatellite markers on a highly representative sampling of 254 individuals of what are presumed to be five Magnolia species. The results support at least three species and maximum five main conservation units. We propose downgrading the latter to four, given morphological, ecological, demographical, and geographical considerations. Two out of the three sympatrically occurring species in the rainforest in the Los Tuxtlas volcanic area have weak genetic evidence to be considered separate species. Similarly, the individuals in the Sierra de Zongolica in central Veracruz, who bear a very high morphological and genetic similarity to Magnolia mexicana, have weak genetic evidence to be recognised as a separate species. Nonetheless, the individuals could be identified as Magnolia decastroi based on morphology, and further research including the full range of this species is recommended.

Chloroplast genomes are considered to be highly conserved. Nevertheless, differences in their sequences are an important source of phylogenetically informative data. Chloroplast genomes are increasingly applied in evolutionary studies of angiosperms, including Magnoliaceae. Recent studies have focused on resolving the previously debated classification of the family using a phylogenomic approach and chloroplast genome data. However, most Neotropical clades and recently described species have not yet been included in molecular studies. We performed sequencing, assembly, and annotation of 15 chloroplast genomes from Neotropical Magnoliaceae species. We compared the newly assembled chloroplast genomes with 22 chloroplast genomes from across the family, including representatives from each genus and section. Family-wide, the chloroplast genomes presented a length of about 160 kb. The gene content in all species was constant, with 145 genes. The intergenic regions showed a higher level of nucleotide diversity than the coding regions. Differences were higher among genera than within genera. The phylogenetic analysis in Magnolia showed two main clades and corroborated that the current infrageneric classification does not represent natural groups. Although chloroplast genomes are highly conserved in Magnoliaceae, the high level of diversity of the intergenic regions still resulted in an important source of phylogenetically informative data, even for closely related taxa.

Societal Impact Statement: Mexico's extraordinary tree diversity is threatened by the increasing demand for resources because of the tenfold population growth in the last century. The conservation status of trees and both urban and rural livelihoods are also negatively affected by agriculture, mining and tourism. Nearly 60% of the Mexican endemic and near endemic tree species whose conservation status we have assessed for the Red List of the International Union for Conservation of Nature are threatened, almost double the percentage of threatened trees worldwide. If no measures are taken to protect this tree diversity properly, these resources will be forever lost for human sustainability.Summary: Mexico is floristically the fourth most species‐rich country in the world. Currently, 3620 native tree species are reported from this country. Mexico has been a forerunner at global level in recognising the need for plant conservation, yet this is in stark contrast with governmental programmes and actions, past and present that negatively affect(ed) immense areas of primary vegetation. In the framework of the Global Tree Assessment, to date, we have assessed the conservation status of nearly 1500 Mexican endemic and near endemic tree species for the International Union for the Conservation of Nature (IUCN) Red List, the distribution data of which we use here for a first meta‐analysis of conservation statuses and spatial distribution patterns in a newly delimited area we call Natural Mexico. Our database consists of 112,416 taxonomically and geographically very carefully curated distribution points of 1474 tree species endemic to Mexico and adjacent areas, belonging to 98 flowering plant families. The extensive curation methodology we consider essential for both research and conservation purposes is emphasised. Nearly 60% of the assessed tree species are threatened, almost double the percentage of threatened arborescent species at global level. Tropical rainforests and cloud forests house the highest proportions of threatened trees. These assessments have an extensive impact, as they not only are the starting point of urgent species conservation actions but also allow for comprehensive studies including extinction risk estimation, gap analyses for conservation planning and species reintroductions, all this in a framework of land use change, climate change and landscape composition and configuration.

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.

Background: The Neotropics are considered one of the most biodiverse areas in the world, housing at least one third of all vascular plant species. One of the genera that has diversified in the Neotropics is Magnolia, with about 174 species of three sections (Macrophylla, Magnolia and Talauma) endemic to the Americas. In this work, we study the biogeographic history of the Neotropical Magnolia species using high-throughput sequencing data. Sequences from 39 species (38 from Magnolia and one from the sister genus Liriodendron) were assembled. The dataset contained sequences from 239 nuclear targets and complete chloroplast genomes. Phylogenomic hypotheses and the ancestral distribution range of Magnolia were reconstructed. Results: The results of the calibrated phylogenetic hypotheses and ancestral range construction suggest that the earliest arrival in the Neotropics were the ancestors of section Talauma (38 million years ago), which colonized the Pacific region. This early presence in South America suggests long-distance, overwater dispersal from North America, the presumed origin of the genus Magnolia. The analysis and the extant Talauma distribution indicate a south to north recolonization. The ancestors of the other two Neotropical sections, Magnolia and Macrophylla, migrated around 19 mya from Asia to North America, radiating southward to the Neotropics afterwards, around 11 mya. Conclusions: Our results suggest that Neotropical magnolias originated from a North American ancestor. The current sections arrived at the region independently influenced by climatic processes such as temperature drops or the Miocene Climatic Optimum. Additionally, geological processes, such as the movement of the South and North American land masses and the emergence of the Panama isthmus, facilitated the migration between continents.

In the last two decades, approximately 80 new Magnolia species have been described from the Neotropics; thus this region now hosts almost half of the world’s known Magnolia diversity. Many of these likely are not segregate taxa but rather separate populations or groups of populations of the previously broadly circumscribed, widespread species. Such is possibly the case of the Magnolia dealbata species complex (belonging to Magnolia sect. Macrophylla), distributed throughout the Sierra Madre Oriental mountain range in Eastern Mexico. This species complex has been divided into six morphospecies based on morphological criteria only. However, recent microsatellite markers have suggested that these may be a single entity. Considering geographical data and the isolation of populations, we hypothesised that the different morphospecies could form two entities, corresponding to the north and centre of the Sierra Madre Oriental. This hypothesis was tested by morphological observations, chloroplast comparisons and phylogenetic analyses of plastomes, angiosperm DNA plastid barcodes and Magnolia-specific plastid DNA barcodes from hypervariable regions. Phylogenetic results from plastomes and angiosperm DNA plastid barcodes refute the multispecies hypothesis and show that the six morphospecies of this complex inhabiting the Sierra Madre Oriental form a single entity. Evidence is also provided that the morphological characters used to delimit the morphospecies of the complex, mainly numbers of carpels and the absence-presence and colour of a spot in the petals, are, in fact, phenotypic variation and have no taxonomic significance. Therefore, the taxa M. alejandrae, M. nuevoleonensis, M. rzedowskiana, M. vovidesii and M. zotictla are synonymised here under M. dealbata. However, the possibility remains of including the latter as a variety of M. macrophylla, based on the results of the Magnolia-specific plastid DNA barcodes. Furthermore, this study proposes an updated conservation status for M. dealbata, highlighting the urgent need for effective conservation measures. The taxonomic clarification presented here is essential to properly target such efforts, especially in the face of threats such as indiscriminate collection and vulnerability to environmental disturbance.