The analysis was conducted under the Global Conservation Consortia framework by the GCCErica working group, which drew on taxonomic records, occurrence data, protected-area coverage, conservation assessments and PlantSearch records. Researchers consolidated names through World Flora Online, filtered Global Biodiversity Information Facility occurrences to produce three increasingly precise datasets, compared South African distributions with protected areas, and assessed representation in seed banks and botanic gardens. Working groups also discussed obstacles, required actions and measures of success in March 2025.

World Flora Online documented 830 accepted non-hybrid species in June 2025, alongside 20 accepted non-horticultural hybrid names. The genus contains 1,214 taxa when species, subspecies and varieties represented in the identification aid are counted. All accepted subspecific taxa are included in the Erica Identification Aid, but 220, all from South Africa, are not character coded.

Of 572,990 occurrence records retained initially, the most precise filtering stage retained 388,411 records representing 782 species and 1,026 taxa. This represented reductions of 32% in records, 7% in species and 13% in taxa compared with the first filter. Among non-hybrid taxa represented in GBIF, seven species, comprising 61 taxa, had no records; 656 species had been recorded within the previous 10 years.

Threat coverage was broad but uneven. About 90% of species had been assessed, but 53 species were Data Deficient and 518 had not been assessed within the preceding 10 years. The source combined South African Red List and IUCN assessments, noting that many South African assessments relied on the 2009 assessment and later updates, while most species outside South Africa, including nearly all Malagasy species, lacked assessments.

Ex situ representation was concentrated among common European and northern species. Of 830 species, 209 were held by the Millennium Seed Bank, 230 occurred in two or more collections, 187 were represented in one collection and 413 were not known to be held in any collection. Among threatened species, 32 of 48 Endangered and 44 of 95 Vulnerable species were absent from ex situ collections. Critically Endangered and Endangered accessions were concentrated mainly in SANBI gardens and the Millennium Seed Bank, which together held 88 of 109 such accessions.

The analysis also identified major ecological and research gaps. Pollinators had been identified for only 1.8% of Erica species, and seed longevity, dispersal and germination requirements remained poorly studied. Around one-third of species lacked DNA sequence data, limiting reliable inclusion in phylogenetic analyses, while undescribed diversity and unclear species or subspecies boundaries persisted.

The authors concluded that threatened-species coverage remains below the Convention on Biological Diversity target of 75%, although the available collection data provide a minimum estimate rather than a complete accession-level assessment. The Erica Identification Aid can support prioritisation, but further collection-level data, updated threat assessments, targeted fieldwork and improved ecological knowledge are required to guide in situ protection, cultivation and the development of distributed metacollections.

Subject of Research: Conservation status and collection gaps for the flowering plant genus Erica

Article Title: Conservation gap analysis for Erica ( Ericaceae )

Article References: Pirie, M. D., Bester, S. P., Blackhall-Miles, R., Coetzee, A., Crowley, D., Ebrahim, I., Elliott, A. C., Fagúndez, J., Forest, F., Forshaw, N., Hoekstra, R. D., Kandziora, M., Klopper, R. R., Koopman, R., Musker, S. D., Nürk, N. M., Osborne, J., Pasta, S., Pipins, S., … Wilman, V. (2026). Conservation gap analysis for Erica (Ericaceae). Nature Conservation, 63, 199-236. https://doi.org/10.3897/natureconservation.63.175466

Image Credits: AI Generated

DOI: 10.3897/natureconservation.63.175466

Keywords: Erica, Ericaceae, conservation gap analysis, ex situ conservation, botanic gardens, seed banks, threat assessment, biodiversity data, plant taxonomy, South Africa, Conservation, analysis

The researchers described the new species and determined that the previously published V. rubescens is conspecific with V. ardisioides, resolving a taxonomic confusion involving both names. Vaccinium is a large genus in the heath family, Ericaceae, with approximately 485 species distributed worldwide. China has recorded 105 species, including the recently described V. dehongense and V. longisetosum.

Yunnan Province contains about 50 species and has the greatest recorded diversity of the genus in China. V. fangianum was named in honor of Prof. Rhui-Cheng Fang, who has contributed substantially to knowledge of Vaccinium in China.

Its Chinese name is 瑞征越橘, pronounced ruì zhēng yuè jú. The formal description is based principally on the specimen collected at Maku Village in Gongshan County on 8 March 2023. The new species differs from V. ardisioides in both vegetative and reproductive morphology.

Its leaf blades are ovate-lanceolate to ovate, 6 to 14 centimeters long and 3 to 6 centimeters wide, with length-to-width ratios of 1.8 to 2.6 and the widest point near the base. The leaves of V. ardisioides are elliptic to oblong-lanceolate, 7.5 to 13 centimeters long and 2.5 to 4 centimeters wide, with ratios of 3 to 3.5 and their widest point near the middle. V. fangianum has eight to 12 pairs of lateral veins, compared with 10 to 16 pairs in V. ardisioides.

Floral characters provide further separation between the two species. The calyx limb of V. fangianum is nearly divided to the base, with narrowly triangular lobes about 1.5 millimeters long and no apical gland. In V. ardisioides, the calyx limb is divided by less than half and carries broadly triangular lobes measuring 0.5 to 1 millimeter, each ending in a gland.

The corolla of V. fangianum is yellowish green, tubular and five-angled, 7 to 9 millimeters long, and villous on its internal surface. That of V. ardisioides is white-pinkish or pinkish, sometimes turning purplish red later, and is glabrous internally. The tubular portions of the anthers in V. fangianum are about 1.7 times as long as the pollen-bearing thecae and lack the two short abaxial spurs found in V. ardisioides.

Both plants are evergreen shrubs that grow epiphytically on trees, but they differ in stature and in the structure of their inflorescences and fruits. V. fangianum is 0.5 to 1.2 meters tall, with axillary racemes 5 to 10 centimeters long and usually 24 to 35 flowers, although some inflorescences have only 10. Its greenish clavate pedicels measure 6 to 7.5 millimeters.

V. ardisioides can be 2 meters tall and has racemes 6 to 11 centimeters long, generally bearing 17 to 27 flowers but sometimes only 10. Its pedicels are 7 to 15 millimeters long. The fruit of the new species is ellipsoid, about 3 millimeters in diameter, changing from yellowish green to purplish red and finally white with a purple tinge.

The globose fruit of V. ardisioides measures 4 to 6 millimeters and becomes purple-black at maturity. The original description of V. ardisioides was published in 1882 from two collections made in Myanmar by T. Lobb and C.

Parish. Most flowers on both type specimens remained young and unopened, and only one had a torn corolla that exposed short lobes. This limited material contributed to uncertainty over the description of the corolla.

Chinese specimens from southwest Yunnan had been reported to differ from the protologue in inflorescence length, pedicel length and the degree of corolla division. Examination of the type collections and numerous additional specimens showed that the inflorescences and pedicels of the Chinese material were longer than those preserved on the young type specimens. The flowers of the southwest Yunnan populations consistently had the shallowly lobed corolla attributed by the authors to the true V. ardisioides.

That history also explains the description of V. rubescens in 1999 from southwest Yunnan. The types and paratypes of that name were found to agree with V. ardisioides in key characters, including five to seven pseudo-whorled leaves, subsessile petioles, leathery oblong-lanceolate blades, raised veins, entire margins, many-flowered axillary racemes, purplish-red angular rachises, clavate pedicels and anthers with two short abaxial spurs. On the basis of these agreements, the study treats V. rubescens as a synonym of V. ardisioides.

It also provides a revised account of V. ardisioides because the protologue and the earlier Flora of China treatment contained inaccurate floral descriptions. The new species is currently known only from Dulongjiang Township in Gongshan County, where it grows epiphytically on tree trunks in evergreen broad-leaved and mixed forests at elevations of 1,200 to 1,500 meters. Flowering occurs from March to April, and fruiting from May to July.

Its type locality is close to the China–Myanmar border, and the authors consider it likely that the species may also occur in adjacent northeastern Myanmar, but field investigations have not confirmed that distribution. The species is therefore assessed as Data Deficient under the IUCN Red List categories. Its documented occurrence is restricted, while its actual range and population status remain uncertain.

V. ardisioides has a substantially wider documented distribution. It occurs in southwest Yunnan, eastern Myanmar and northwestern Thailand, usually as an epiphyte in evergreen broad-leaved forests or along riversides at elevations of 1,400 to 2,500 meters. Flowering and fruiting extend from February to June.

More than 20 locations have been recorded, and the study estimates an extent of occurrence of approximately 280,000 square kilometers. Based on specimen records, its relatively broad range and the absence of observed evidence of severe population decline, the authors assess V. ardisioides as Least Concern. The two species therefore have both clearly distinguished diagnostic features and different levels of distributional documentation.

Within the genus, V. fangianum is assigned to V. sect. Epigynium because it is evergreen, has pseudo-verticillate leaves, elongated racemose inflorescences and anthers without dorsal spurs. Most species in that section have serrated leaf margins, whereas V. fangianum and V. ardisioides have entire blades, a combination the authors describe as unique within the section.

The new species is also geographically separated from V. ardisioides: V. fangianum is recorded in northwestern Yunnan, while V. ardisioides occurs in southwestern Yunnan, southeastern Myanmar and western Thailand. The study presents V. fangianum as a distinct taxonomic entity and uses herbarium and field comparisons to establish its diagnostic combination of leaf, calyx, corolla, anther and fruit characters.

Subject of Research: Taxonomic description of Vaccinium fangianum and revision of Vaccinium ardisioides in Yunnan, China

Article Title: Vaccinium fangianum ( Ericaceae ), a new species from Northwest Yunnan, China, with critical notes on V. ardisioides

Article References: Liang, X.-H., Ni, J.-B., & Tong, Y.-H. (2026). Vaccinium fangianum (Ericaceae), a new species from Northwest Yunnan, China, with critical notes on V. ardisioides. PhytoKeys, 275, 61-71. https://doi.org/10.3897/phytokeys.275.197108

Image Credits: AI Generated

DOI: 10.3897/phytokeys.275.197108

Keywords: Vaccinium fangianum, Vaccinium ardisioides, plant taxonomy, species description, Ericaceae, Dulongjiang, northwestern Yunnan, epiphytic shrub, herbarium taxonomy, conservation assessment, Vaccinium, fangianum

The genome was built from wild-collected material. Young, disease-free leaves were sampled in the Dabie Mountains at an elevation of roughly 1,005 meters, dried in silica, and preserved for laboratory work. Specimens were identified by a doctoral-level botanist and deposited in the Huanggang Normal University Herbarium in Hubei province. High-molecular-weight DNA was extracted, quality-checked on agarose gels, and quantified spectrophotometrically before the team constructed paired-end Illumina libraries and sequenced them on a NovaSeq6000 platform. After filtering with SOAPnuke, the pipeline retained more than 19.3 million clean reads totaling about 2.89 gigabases, with a GC content of 39.52 percent and quality scores comfortably above standard thresholds. De novo assembly with GetOrganelle, followed by validation with BOWTIE2 mapping, produced a closed circular plastome that was annotated with DOGMA and CPGAVAS tools and manually verified in Geneious before submission to GenBank under accession OM161981.

The assembled molecule measures 203,480 base pairs and displays the canonical quadripartite architecture familiar from most angiosperm plastomes: a large single-copy region of 113,715 base pairs, a small single-copy region of 7,953 base pairs, and a pair of identical inverted repeat regions of 40,918 base pairs each that separate the two single-copy segments. Annotation yielded 151 unique genes, of which 98 encode proteins, 45 are transfer RNAs and eight are ribosomal RNAs. The protein-coding set includes a full complement of 55 photosynthesis-related genes, spanning the ATP synthase, photosystem I, photosystem II, NADH-dehydrogenase and cytochrome b/f complexes together with the rubisco large subunit rbcL, alongside genes for self-replication functions such as ribosomal proteins, RNA polymerase subunits and the translational initiation factor infA. A single copy of the accD gene, which encodes a subunit of acetyl-CoA carboxylase and has been implicated in adaptation to specific ecological niches during dicot radiation, is also present, along with conserved open reading frames ycf3 and ycf4. Sixteen genes carry introns, and all but ycf3 and accD follow the conventional two-exon, one-intron arrangement.

Codon usage patterns in the protein-coding sequences reveal the same asymmetries seen in many other plastomes. Across 40,013 codons, leucine is the most abundant amino acid at 10.477 percent, followed by isoleucine and glycine, while cysteine and tryptophan are the rarest. Relative synonymous codon usage analysis flagged 30 codons with clear preference, and 29 of those end in A or U rather than C or G. This A/U-ending bias, an outcome of mutation pressure and translational selection, matches the pattern previously reported for other flowering plant chloroplast genomes and provides useful context for anyone optimizing heterologous gene expression or reconstructing selective dynamics in Ericaceae plastids.

Diversity analysis across eleven fully sequenced Rhododendron plastomes identified the mutational hotspots that matter most for species-level discrimination. Nucleotide diversity values ranged from zero to 0.06896, with the small single-copy region the most variable compartment, the large single-copy region intermediate, and the inverted repeats the most conserved by a wide margin. Six gene regions exceeded the practical hotspot threshold of Pi greater than 0.02: trnI-GAU, trnG-UCC, rps3, rps12, trnV-UAC and trnK-UUU. Several of these, including matK relatives and rbcL-adjacent loci, echo the genes long used as DNA barcodes, but the newly flagged trn and ribosomal protein loci offer fresh candidates for markers tailored specifically to Rhododendron and its relatives.

Microsatellite scanning adds another layer of marker resources. The R. mariesii plastome harbors 70 simple sequence repeats, five of them in compound arrangements. The overwhelming majority, 65 repeats or roughly 93 percent, are mononucleotide motifs, and A/T repeats dominate at 91.4 percent, with C/G repeats nearly absent. Dinucleotide, trinucleotide and hexanucleotide motifs are present only as singletons or pairs, including one (AAGGGT/ACCCTT)5 hexamer. Most repeats sit in intergenic spacers, though 28 were found within the rpl16 gene and the remainder scattered across genes such as ccsA, cemA, ndhA, rpoA, rpoC2, rps7, rps8 and trnL-UAA. Compared with plastomes of other woody plants, the count is higher than in mango or Spondias bahiensis but far lower than in Syringa pinnatifolia, reinforcing that microsatellite density varies widely even among conserved plastid genomes.

Comparative alignment across the eleven Rhododendron plastomes showed high overall similarity with no rearrangements or inversions, confirming that structural conservatism is the rule in this genus. Coding regions were consistently more conserved than non-coding ones, and the most divergent coding loci, including rpoB, rpoC2, rps8, petD, rpl23, rpl22 and ndhF, owed their variability largely to intron content. The most variable stretches lie in intergenic spacers such as trnK-pafI, atpE-rpoB, trnT-rpl14, rpoA-psbJ, rpl20-trnE, ndhI-rps19 and rpl16-ndhI, regions that, under near-neutral evolution, accumulate substitutions with little interference from natural selection and therefore carry a legible record of lineage history.

The most striking structural finding concerns the inverted repeat boundaries. Even though overall gene order is stable, the edges of the IR expand and contract dramatically across the genus, and the authors argue this boundary drift is the main driver of plastome size differences among related Ericaceae. Rhododendron mariesii’s plastome, at 203,480 base pairs, is larger than those of R. pulchrum, R. simsii, R. molle, R. delavayi and R. platypodum, yet smaller than those of R. kawakamii, R. micranthum, R. henanense, R. griersonianum, R. concinnum and R. datiandingense. Junction mapping shows the LSC-IR border landing between different gene pairs in different species, with genes such as trnV, ycf15 and rps12 variously stretched across or excluded from the repeat, while the SSC-side boundary shifts the position of ndhF and rps15 relative to the repeats. These differences in gene content and placement at the junctions are precisely the kind of comparative signal that phylogeneticists exploit when reconstructing deep relationships.

Phylogenetic reconstruction pulled together 22 complete Ericaceae plastomes, including twelve Rhododendron species plus representatives of Vaccinium, Arbutus, Gaultheria and several mycoheterotrophic lineages, with Pyrola rotundifolia as an outgroup. Maximum-likelihood analysis under 1,000 bootstrap replicates placed all Ericaceae taxa in a single clade split into two subclades, a topology consistent with previously published work, and nestled R. mariesii closest to R. simsii and R. pulchrum. The species of Arbutus, Hemitomes, Allotropa, Monotropa, Pityopus, Vaccinium and Gaultheria branched as distant relatives, underscoring how much phylogenetic resolution a single well-assembled plastome can add at the genus and family level.

The practical stakes extend beyond systematics. Rhododendron mariesii occupies a critical place in the woodland ecology of the Dabie Mountains, but habitat fragmentation, booming Rhododendron-themed tourism and human activity are squeezing wild populations, and the species’ limited genomic resources have long hindered population genetic and conservation work. A complete, well-annotated plastome with a catalog of hotspots and microsatellites gives conservation geneticists immediately usable markers for phylogeography and population monitoring, and gives breeders a reference for tracing maternally inherited lineages in hybrid programs. More broadly, the study reinforces a now-familiar lesson of plastid genomics: chloroplast genomes evolve slowly and conservatively in structure, yet it is precisely their small set of labile boundaries and hotspot loci that carry the information needed to tell closely related species apart. For the heath family, this new reference is a foundation on which future barcoding, phylogenetic and ecological research across Ericaceae can be built.

Subject of Research: Complete chloroplast genome sequencing and comparative genomics of Rhododendron mariesii and related Ericaceae species

Article Title: Complete chloroplast genome sequence of Rhododendron mariesii and comparative genomics of related species in the family Ericaeae

Article References: Li, Z., Huang, Z., Wan, X., Yu, J., Dong, H., Zhang, J., Zhang, C., & Wang, S. (2023). Complete chloroplast genome sequence of Rhododendron mariesii and comparative genomics of related species in the family Ericaeae. Comparative Cytogenetics, 17, 163-180. https://doi.org/10.3897/compcytogen.17.101427

Image Credits: AI Generated

DOI: 10.3897/compcytogen.17.101427

Keywords: chloroplast genome, Rhododendron mariesii, Ericaceae, plastome, phylogenetics, DNA barcoding, microsatellites, nucleotide diversity, inverted repeats, codon usage, conservation genetics, Dabie Mountains

The findings stem from a field excursion in early June 2023 through the Serra do Marão, Serra do Alvão, Serra do Barroso and Serra do Gerês, mountain chains in northern Portugal where the species occurs alongside populations in northwest Spain. In small remnants of the original oak forest, consisting of Quercus pyrenaica, Q. cerris, Erica species and various broom shrubs, the researcher found both larvae and adult beetles of Donus proximus. A targeted search then revealed Erica umbellata as the host plant, with the insects concentrated on forest clearings and edges, usually near rock formations or paths.

The larvae themselves are striking. They carry a high-contrast pattern of five pale longitudinal stripes on a green body colour, an arrangement that camouflages them superbly among the branches of their host plant. Like other Hyperinae, the larvae feed externally on the plant, a lifestyle that makes them relatively easy to observe in the field during early summer and that has repeatedly proven useful for uncovering host-plant associations in this subfamily.

Rearing the larvae on Erica umbellata in the laboratory proceeded without difficulty. Within one week, the first larvae began spinning a reddish-brown silken net cocoon, a characteristic structure for the group. Pupation followed within three to four days, and by 19 June, fourteen to eighteen days after pupation, all adult beetles had emerged. This successful rearing confirmed the host-plant association beyond doubt, since the larvae had been collected in the field and completed their development on the suspected host.

Beyond the biological novelty, the study settles a taxonomic question that has lingered for decades. Capiomont described the species in 1876 as Hypera proxima on the basis of a single male specimen, noting that it was the only individual he could examine. He compared the new species with Donus montivagus, which he had described from the Sierra Nevada in southern Spain. The type locality of Donus proximus lies in the Serra do Gerês in northern Portugal, where L. von Heyden captured the specimen.

The holotype itself survives in the collection of Lucas von Heyden at the Senckenberg German Entomological Institute in Müncheberg, and photographs of the type allowed its identity to be verified without difficulty. Additional comparison material from the collection Georg Frey at the Natural History Museum Basel, including specimens from Asturias and León in Spain and from Sabrosa and S. Martinho in Portugal, together with topotypic animals from the Serra do Gerês and specimens of the synonym Donus barrosi, made it possible to examine the species thoroughly.

The conclusion was unambiguous: Donus proximus does not belong to the genus Brachypera, as had been proposed in 2008, but to the genus Donus. The oval shape of the elytra without a humeral bulge, the comparatively short and broad abdominal segments, the strongly rounded pronotum and the long, cylindrical rostrum all match the characteristic features of Donus. The new combination Donus proximus comb. nov. is therefore introduced. One larval character was not checked: the number of teeth on the larval mandibles, which should be three in Donus, four in Brachypera and only two in Hypera. This trait has so far been examined in only six of the more than forty species of Brachypera and should be verified in future studies.

The habitat records are equally significant. All sites lay on clearings or at the edges of near-natural oak forest, mostly close to rock formations or paths. The study characterises this environment for the first time for the species and highlights how restricted it has become. Much of today’s forest cover in northern Portugal consists of plantations of Aleppo pine, Eucalyptus, Thuja or Acacia, all foreign to the original ecosystem, and the natural oak woods have been severely reduced.

That pressure is not merely historical. Slash-and-burn clearing, unusually frequent forest fires and afforestation with non-native tree species continue to threaten the remaining oak forests, and the same threats apply directly to Donus proximus. Earlier records from near the coast, such as those of the synonym barrosi from the coastal locality of San Martinho, almost certainly no longer persist, given how degraded those habitats have become. The remaining forests in the northern sierras are therefore the last refuges for this weevil in Portugal.

The study also underscores how incomplete our knowledge of weevil host associations remains. A 2005 compilation gathered fifteen different plant families known to support Hyperinae development, and Ericaceae were not among them. Because no comprehensive revision of all Donus species exists, and the most recent summarising works date back to the nineteenth and early twentieth centuries, with only partial modern revisions available, adjustments of this kind are not surprising. The combination of field observation, successful rearing and type verification shows how classical methods can still resolve both the identity and the ecology of an obscure species in a single effort.

Subject of Research: Biology, host-plant association and taxonomic identity of the weevil Donus proximus in northern Portugal

Article Title: Zu Biologie und Identität von Donus proximus (Capiomont, 1876) comb. nov. ( Coleoptera , Curculionidae , Hyperinae )

Article References: Germann, C. (2023). Zu Biologie und Identität von Donus proximus (Capiomont, 1876) comb. nov. (Coleoptera, Curculionidae, Hyperinae). Alpine Entomology, 7, 213-217. https://doi.org/10.3897/alpento.7.109422

Image Credits: AI Generated

DOI: 10.3897/alpento.7.109422

Keywords: Donus proximus, Curculionidae, Hyperinae, Erica umbellata, Ericaceae, taxonomy, comb. nov, northern Portugal, oak forests, larval rearing, Serra do Gerês, habitat loss

The research team collected scale-leaf tissue from M. callistoma in Shiyan, Hubei Province, and sequenced it on an Illumina HiSeq 4000 platform at a mean depth of over 900-fold. Assembly with GetOrganelle and polishing with Pilon produced a single circular plastome of 29,784 base pairs with a GC content of 30.8 percent. That figure might sound unremarkable until compared with a typical photosynthetic plant, whose plastome runs roughly 150,000 base pairs and carries more than a hundred genes. The M. callistoma plastome contains just 40 genes: 20 protein-coding genes, 16 transfer RNAs, and four ribosomal RNAs. Strikingly, the canonical quadripartite structure found in almost all land plant plastids, with two inverted repeats separating large and small single-copy regions, is entirely absent. No inverted-repeat boundaries could be detected at all.

The gene inventory tells the story of a genome in terminal decline. Every photosynthetic function has been erased. There are no photosystem subunits, no NADH dehydrogenase genes, no cytochrome b6f complex components, no ATP synthase subunits, and no rubisco large subunit. What remains is essentially a minimal housekeeping kit: ten genes for small ribosomal subunit proteins, seven for large subunit proteins, and just three other coding genes, infA, matK, and accD. Four of the retained genes carry a single intron. This is the genomic signature of an organelle whose core reason for existence, photosynthesis, has been outsourced to fungal partners, leaving relaxed selection to strip away everything the plant no longer needs.

To place this genome in context, the researchers compiled published plastomes from 30 mycoheterotrophic species across six families, ranging from orchids such as Gastrodia and Lecanorchis to the bizarre holoparasites Sciaphila and Mitrastemon. The comparison revealed a spectrum of decay. Sciaphila thaidanica and Mitrastemon yamamotoi carry plastomes of only about 20 kilobases, among the smallest known in flowering plants, while at the other extreme some Burmannia species retain genomes approaching 100 kilobases. GC content showed a weak but statistically significant positive correlation with genome size, suggesting that as these genomes shrink, their nucleotide composition shifts in parallel. Within Monotropoideae itself, Pterospora andromedea holds the largest plastome at roughly 40 kilobases, while the more recently diverged Monotropa uniflora has the smallest at about 27 kilobases.

Whole-genome alignments exposed another dimension of decay: the collapse of synteny, the conserved order of genes along the chromosome. Among Monotropoideae species, gene order is scrambled, particularly in Hypopitys, Monotropsis, Monotropastrum, and Monotropa. Fragment loss has accumulated in more recently diverged lineages, so that even within the genus Monotropa, where synteny is relatively well preserved, the overall picture across the subfamily is one of progressive disintegration. Ancestral-state reconstruction across the 30 species showed that losses of the large genes ycf1 and ycf2 occurred convergently among eudicot lineages, while all sampled Monotropa species lacked rps23, pointing to a lineage-specific loss within that genus.

The phylogenomic analysis went beyond genome description to resolve long-standing questions about relationships within Ericaceae. Using a concatenated alignment of plastid protein-coding genes nearly 48,000 base pairs long, with Actinidia chinensis as an outgroup, the team recovered a well-supported split into two major clades. Clade 1 united Pyroloideae, Arbutoideae, and Monotropoideae, with Pyroloideae branching earliest and Monotropoideae emerging as the youngest lineage. Within Monotropoideae, the sampling covered 10 of the 12 recognized genera and achieved maximum bootstrap support of 100 for the backbone. Pterospora and Sarcodes occupied successive early-branching positions, followed by Pleuricospora, while a clade of Monotropsis, Monotropastrum, and Monotropa was sister to a group containing Allotropa, Hemitomes, Pityopus, and Hypopitys. Clade 2 comprised the core Ericaceae, subdivided into Vaccinioideae and Ericoideae.

Divergence dating with fossil calibrations placed the split between Pyroloideae and the remaining subfamilies at approximately 67.77 million years ago, in the latest Cretaceous. Arbutoideae and Monotropoideae diverged around 66.57 million years ago, and diversification within Monotropoideae began about 63.35 million years ago, immediately after the end-Cretaceous extinction. The genus-level splits came much later: Sarcodes and Pterospora separated roughly 45.79 million years ago, Monotropsis split from the lineage leading to Monotropa and Monotropastrum about 39.73 million years ago, and those two genera diverged about 26.74 million years ago. The rapid radiation of Rhododendron and Vaccinium, by contrast, occurred only around 1 to 2 million years ago.

Perhaps the most striking finding concerns geography. Ancestral-range estimation using the DIVALIKE+J model in RASP placed the most recent common ancestor of Clade 1 in Asia during the late Cretaceous to early Cenozoic. From there, the lineage dispersed to North America, most plausibly across the Bering Land Bridge, which connected the continents from the latest Cretaceous into the early Paleocene, when a warm, humid belt of deciduous broadleaf forest stretched across the region. Then came a remarkable reversal: the ancestor of the Monotropsis, Monotropastrum, and Monotropa lineage appears to have dispersed back to Asia during the late Eocene to early Oligocene, around 39.70 million years ago, giving rise to the East Asian endemics Monotropastrum humile and Monotropa callistoma. The ghost plants, in other words, crossed the world twice.

The comparative analysis also yielded a testable hypothesis about the order in which plastid genes are lost as plants abandon photosynthesis. Across the 30 species examined, the ndh genes were absent everywhere, followed by photosystem, cytochrome, rubisco, and ycf3/4 genes, then the RNA polymerase genes, then atp genes, and finally the ribosomal, transfer RNA, and housekeeping genes such as accD, clpP, and matK. The sole exception was Burmannia cryptopetala, which retains atp genes, a pattern associated with mixotrophic or partially parasitic lifestyles. The team proposes that the degree of a plant’s absolute dependence on fungal hosts correlates with the breadth of plastid gene loss, with Monotropa, whose plastid genes evolve roughly 13 times faster than its nuclear genes, representing an advanced stage of degradation in which even clpP has been discarded.

Yet the decay is not random, and that is the deeper lesson of the study. Housekeeping genes persist with remarkable consistency: accD, which catalyzes the first committed step of fatty acid biosynthesis and is essential for building the plastid’s own membranes, was retained in every single mycoheterotrophic species examined. The retention of matK across all Monotropoideae and Burmanniaceae, despite its patchy record in orchids, and the lineage-specific survival of ycf1 and ycf2 in some orchids and Burmanniaceae but not others, show that different lineages face different residual functional constraints. The endpoints of plastid genome reduction form a spectrum rather than a single destination, ranging from the streamlined but intact genomes of Monotropoideae to the complete loss of the plastid genome in Balanophora, which has transferred even accD to the nucleus. When an organelle’s core function is outsourced, its genetic system converges, again and again across independent lineages, toward the same extreme simplification. The ghost plants of Asia and North America, silent and white beneath the forest canopy, are carrying out that experiment in real time, and their genomes are the record.

Subject of Research: Plastome evolution and phylogenomics of the mycoheterotrophic subfamily Monotropoideae (Ericaceae)

Article Title: Phylogenomics Clarifies Plastome Reduction and Phylogenetic Relationships in Monotropoideae

Article References: Deng, G., Duan, K., Xiang, N., Gao, F., Zhan, P., Shu, R., Lin, Q., Zuo, Q., & Yuan, T. (2026). Phylogenomics Clarifies Plastome Reduction and Phylogenetic Relationships in Monotropoideae. Ecology and Evolution, 16(10), Article e74449. https://doi.org/10.1002/ece3.74449

Image Credits: AI Generated

DOI: 10.1002/ece3.74449

Keywords: Monotropoideae, mycoheterotrophy, plastome reduction, Ericaceae, Monotropa callistoma, phylogenomics, Bering Land Bridge, biogeography, gene loss, relaxed selection, ghost plants, divergence dating