Phylogenomic evolutionary insights in the fern family Gleicheniaceae

Genome skimming provides evidence to accept two new genera (Apiaceae) separated from the Peucedanum s.l

Background

The Peucedanum s.l. genus, the backbone member of subfamily Apioideae, includes many medically and economically important plants. Although previous studies have proved that the genus was not a natural taxonomic unit and taxonomists also conducted several taxonomic revisions for taxa of this genus, classifications of numerous taxa of the genus still have not been satisfactorily resolved, especially for those endemic to China. Therefore, we conducted a comprehensive taxonomic revision of taxa within the polyphyletic Peucedanum s.l. genus in this study.

Methods

We used two molecular datasets (103 plastomes and 43 nrDNA sequences) generated by genome skimming to reconstructed a reliable phylogenetic framework with high support and resolution. In addition, we also investigated the divergence time of core clade of endemic taxa.

Results and Discussion

Both analyses failed to recover Peucedanum s.l. as a monophyletic group and robustly supported that P. morisonii, the representative of Peucedanum s.s., was distantly related to other Peucedanum s.l. members, which implied that these Peucedanum s.l. taxa were not "truly Peucedanum plants". Among these Peucedanum s.l. members, plastid-based phylogenies recognized two monophyletic clades, clade A (four species) and clade B (10 taxa). Meanwhile, obvious recognized features for morphology, plastome, and chromosome number for each clade were detected: dorsally compressed and glabrous mericarps with filiform dorsal ribs, winged lateral ribs, numerous vittae in commissure and each furrow, IRa/LSC border falling into rpl23 gene, an overall plastome size of 152,288-154,686 bp, and chromosome numbers of 2n=20 were found in clade A; whereas dorsally compressed and pubescent mericarps with filiform dorsal ribs, winged lateral ribs, numerous vittae in commissure and each furrow, IRa/LSC border falling into the ycf2 gene, an overall plastome size of 146,718-147,592 bp, and chromosome numbers of 2n=22 were discovered in clade B. Therefore, we established two new genera (Shanopeucedanum gen. nov. and Sinopeucedanum gen. nov.) to respectively accommodate the taxa of clades A and B. Furthermore, molecular dating analysis showed that the diversification of clades A and B occurred in the early Pleistocene and late Pliocene, respectively, which may have been driven by the complex geological and climate shifts of these periods. In summary, our study impelled a revision of Peucedanum s.l. members and improved the taxonomic system of the Apiaceae family.

Importance of habit and environmental characteristics in shaping patterns of richness and range size of ferns and lycophytes in the Atlantic Forest

PREMISE

Ferns and lycophytes, the two spore-bearing lineages of vascular plants, share a unique life cycle, and because of several morpho-ecophysiological similarities, are usually investigated as a unit, but they may have distinct ecological and environmental responses. Understanding the diversity and distribution patterns of ferns and lycophytes separately is essential for designing effective conservation strategies.

METHODS

We assessed species richness and range sizes using range-diversity analyses and investigated environmental (climatic, edaphic) and ecological (endemism, habit diversity, specialization) predictors of these range and richness metrics using generalized linear models.

RESULTS

The central region of the Atlantic Forest primarily contained areas with fern and lycophyte species with high richness and small ranges; the northern and southern extremes of the forest had species with low richness and larger ranges. Fern richness was associated with a combination of environmental and ecological variables; lycophyte richness was associated only with ecological variables. Range sizes were positively related to habit diversity for both ferns and lycophytes, but the effect of environmental variables differed between the two lineages. Critical areas were primarily not within protected areas.

CONCLUSIONS

Fern range sizes and richness were influenced by a combination of ecological and environmental factors such as temperature, precipitation, and soil variables; only ecological variables influenced lycophyte richness and range sizes. The effects of these factors must be considered separately for the two lineages due to their different responses to stressors. Conservation efforts should increase in the species-rich-low-range areas that are outside protected areas to protect these low-range species.

'Out of Africa' origin of the pantropical staghorn fern genus Platycerium (Polypodiaceae) supported by plastid phylogenomics and biogeographical analysis

BACKGROUND AND AIMS

The staghorn fern genus Platycerium is one of the most commonly grown ornamental ferns, and it evolved to occupy a typical pantropical intercontinental disjunction. However, species-level relationships in the genus have not been well resolved, and the spatiotemporal evolutionary history of the genus also needs to be explored.

METHODS

Plastomes of all the 18 Platycerium species were newly sequenced. Using plastome data, we reconstructed the phylogenetic relationships among Polypodiaceae members with a focus on Platycerium species, and further conducted molecular dating and biogeographical analyses of the genus.

KEY RESULTS

The present analyses yielded a robustly supported phylogenetic hypothesis of Platycerium. Molecular dating results showed that Platycerium split from its sister genus Hovenkampia ~35.2 million years ago (Ma) near the Eocene-Oligocene boundary and began to diverge ~26.3 Ma during the late Oligocene, while multiple speciation events within Platycerium occurred during the middle to late Miocene. Biogeographical analysis suggested that Platycerium originated in tropical Africa and then dispersed eastward to southeast Asia-Australasia and westward to neotropical areas.

CONCLUSIONS

Our analyses using a plastid phylogenomic approach improved our understanding of the species-level relationships within Platycerium. The global climate changes of both the Late Oligocene Warming and the cooling following the mid-Miocene Climate Optimum may have promoted the speciation of Platycerium, and transoceanic long-distance dispersal is the most plausible explanation for the pantropical distribution of the genus today. Our study investigating the biogeographical history of Platycerium provides a case study not only for the formation of the pantropical intercontinental disjunction of this fern genus but also the 'out of Africa' origin of plant lineages.

Prospecting for rare earth element (hyper)accumulators in the Paris Herbarium using X-ray fluorescence spectroscopy reveals new distributional and taxon discoveries

BACKGROUND

Rare earth elements (REEs) are increasingly crucial for modern technologies. Plants could be used as a biogeochemical pathfinder and a tool to extract REEs from deposits. However, a paucity of information on suitable plants for these tasks exists.

METHODS

We aimed to discover new REE-(hyper)accumulating plant species by performing an X-ray fluorescence (XRF) survey at the Herbarium of the Muséum national d'Histoire naturelle (MNHN, Paris, France). We selected specific families based on the likelihood of containing REE-hyperaccumulating species, using known taxa that accumulate REEs. A total of 4425 specimens, taken in the two main evolutionary lineages of extant vascular plants, were analysed, including the two fern families Blechnaceae (n = 561) and Gleicheniaceae (n = 1310), and the two flowering plant families Phytolaccaceae (n = 1137) and Juglandaceae (n = 1417).

KEY RESULTS

Yttrium (Y) was used as a proxy for REEs for methodological reasons, and a total of 268 specimens belonging to the genera Blechnopsis (n = 149), Dicranopteris (n = 75), Gleichenella (n = 32), Phytolacca (n = 6), Carya (n = 4), Juglans (n = 1) and Sticherus (n = 1) were identified with Y concentrations ranging from the limit of detection (LOD) >49 µg g-1 up to 1424 µg g-1. Subsequently, analysis of fragments of selected specimens by inductively coupled plasma atomic emission spectroscopy (ICP-AES) revealed that this translated to up to 6423 µg total REEs g-1 in Dicranopteris linearis and up to 4278 µg total REEs g-1 in Blechnopsis orientalis which are among the highest values ever recorded for REE hyperaccumulation in plants. It also proved the validity of Y as an indicator for REEs in XRF analysis of herbarium specimens. The presence of manganese (Mn) and zinc (Zn) was also studied by XRF in the selected specimens. Mn was detected in 1440 specimens ranging from the detection limit at 116 µg g-1 up to 3807 µg g-1 whilst Zn was detected in 345 specimens ranging from the detection limit at 77 µg g-1 up to 938 µg g-1.

CONCLUSIONS AND IMPLICATIONS

This study led to the discovery of REE accumulation in a range of plant species, substantially higher concentrations in species known to be REE hyperaccumulators, and records of REE hyperaccumulators outside of the well-studied populations in China.