The new species belongs to Elymus, the largest genus in the wheat tribe Triticeae, which encompasses more than 150 perennial species distributed across temperate Asia, Europe and the Americas. In most members of this tribe, including typical Elymus, the inflorescence is a simple, unbranched spike bearing one or a few laterally compressed spikelets per node of the central axis. Branching of the spike axis is exceedingly rare. That is precisely what makes E. chaobotryus so conspicuous: its compound spike, 16 to 19 centimetres long, produces 10 to 15 short lateral branches, each 2 to 4 centimetres long, from nearly all nodes of the main rachis. The branches lengthen from apex to base, creating the hierarchical, grape-cluster outline that inspired the species name, a combination of the collector’s given name and the Latinized Greek botrys, meaning a bunch of grapes.

The discovery traces back to 2019, when seeds were first collected in Guashize Township, Tongren City, in southeastern Qinghai Province. Plants raised from those seeds have been grown continuously since 2020 in a forage germplasm nursery near Qinghai Lake, at roughly 3,200 metres elevation. Across multiple years of cultivation, the diagnostic inflorescence architecture remained stable, and in 2025 replicated field plots were established in Haibei Tibetan Autonomous Prefecture to confirm that the grape-like compound spike persists in both nursery-grown and field-grown plants. This multi-year stability was critical evidence, because superficially complex-looking spikes can sometimes result from overlapping structures, spreading awns, flexuous rachises or poor specimen preservation rather than true branching.

To rule out that possibility, the team conducted an extensive herbarium survey, examining 1,321 specimens of Elymus and related taxa from Qinghai, Gansu, Xinjiang, Tibet, Inner Mongolia and Sichuan. This included 660 specimens of E. dahuricus, the species to which the new grass is phylogenetically closest, as well as hundreds of specimens of E. nutans, E. sibiricus and other regionally occurring species. None of the examined specimens possessed the hierarchical compound-spike organisation characteristic of E. chaobotryus. Several showed lax, flexuous or pendulous spikes that looked superficially branched, but in every case the inflorescence retained a single continuous main rachis and lacked lateral spike-bearing branchlets. The apparent complexity was attributable to loose spikelet arrangement, awn spreading, overlapping culms or specimen pressing.

Beyond the inflorescence, a consistent set of floral and vegetative characters separates the new species from its morphologically similar relatives. Its glumes are lanceolate, 3 to 4 millimetres long, consistently 3-veined, and tipped with very short mucros of less than 0.9 millimetres. The lemmas are comparatively short, 5 to 7 millimetres long and 3-veined, bearing awns of only 3 to 4 millimetres that are densely covered with fine bristles. The leaf blades are conspicuously narrow, just 2 to 5 millimetres wide, with glabrous sheaths and nearly smooth surfaces. The culms are erect, tufted and non-rhizomatous, reaching 80 to 130 centimetres. In E. multiramosus, the other branched-spike species from the plateau, the glumes are distinctly longer at 4 to 7 millimetres with much longer apical awns, the lemmas bear awns of 9 to 12 millimetres, and the leaf blades are broader at 5 to 7 millimetres. E. sibiricus, E. nutans and E. dahuricus var. dahuricus all bear simple, unbranched spikes and differ further in glume and lemma proportions.

Cytogenetic analysis provided an independent line of evidence. Flow cytometry of fresh leaf tissue, using the maize inbred line B73 as an internal standard, estimated a genome size of 11.43 gigabases for E. chaobotryus, closely matching the 11.32 gigabases measured for E. multiramosus and clearly exceeding the 7.10 gigabases of the tetraploid E. sibiricus. Chromosome counts from DAPI-stained root-tip cells confirmed 2n = 42 chromosomes, predominantly metacentric to submetacentric and approximately 5.0 to 8.0 micrometres long. Genomic in situ hybridization, using total genomic DNA of Pseudoroegneria spicata as a probe, identified 14 St-genome chromosomes. Sequential fluorescence in situ hybridization with Oligo-HvCSR and Oligo-pTa535 probes revealed distinct hybridization patterns among the remaining chromosomes, allowing them to be assigned to two groups of 14 each, interpreted as the H and Y genomes. Together, these results support a hexaploid complement of 2n = 6x = 42 and an StHY genomic constitution, the classic allopolyploid signature of Elymus.

Plastome sequencing added the phylogenetic dimension. The complete chloroplast genome of E. chaobotryus is 135,049 base pairs in length with an overall GC content of 38 percent, exhibiting the typical quadripartite architecture of a large single-copy region of 80,661 base pairs, a small single-copy region of 12,772 base pairs, and a pair of inverted repeats of 20,808 base pairs each. A total of 88 genes were annotated. In maximum-likelihood analyses of complete plastome sequences from 56 taxa, conducted in IQ-TREE under the GTR+F+R3 model with 1,000 bootstrap replicates, E. chaobotryus was recovered as sister to E. dahuricus, embedded within the broader Elymus complex. This placement is consistent with the species’ morphological assignment to Elymus and clarifies its maternal evolutionary history.

Particularly noteworthy is what the phylogeny reveals about the branched inflorescences themselves. Despite both possessing strongly compound spikes, E. chaobotryus and E. multiramosus are recovered in different plastome lineages rather than as a single clade. E. multiramosus forms a well-supported sister pair with E. sinosubmuticus in a separate lineage. This pattern indicates that spike branching is not necessarily associated with close maternal relatedness and may have arisen independently in different Elymus lineages. Spike branching therefore remains highly informative for morphological diagnosis but should be interpreted cautiously in phylogenetic inference, a lesson that echoes broader hypotheses in Triticeae suggesting that the unbranched spike may represent a derived condition resulting from reduction of a more highly branched ancestral inflorescence.

The discovery also highlights the plateau’s role as a centre of mountain plant diversity and the ongoing value of integrative taxonomy. The Qinghai-Tibetan Plateau and the adjacent Himalaya-Hengduan Mountains have long been recognized as major centres of diversification for genera such as Gentiana, Pedicularis, Primula and Rhododendron, and recent field work continues to reveal unrecognised St-genome grass taxa there, including E. multiramosus from western Qinghai and Roegneria yenchiana from the Hengduan Mountains. Elymus species are allopolyploids, each possessing one St haplome from Pseudoroegneria combined with additional haplomes from Hordeum, Agropyron, Australopyrum and an enigmatic Y haplome, and this reticulate evolution has long complicated their classification.

There is also a poignant ecological twist. Field surveys documented seven local populations totaling approximately 36 individuals, all discovered in the corner of the walled courtyard of a herder’s house surrounded by extensive alpine steppe. The herder family had temporarily left the homestead for seasonal pasture rotation. The enclosed courtyard may have provided a small refuge where the species could persist and reproduce, whereas in the open steppe its populations are likely subject to intense grazing pressure, which may help explain why its unusual branched inflorescences had long escaped notice. With so few known individuals and a distribution restricted to a small area of Tongren City, the species’ long-term persistence remains uncertain, and the researchers suggest that compound-spike architecture should be explicitly scored and incorporated into identification keys for Elymus to ensure that such distinctive plants are not overlooked in future surveys.

Subject of Research: Botany

Article Title: Elymus chaobotryus ( Poaceae ), a new species from the north-eastern Qinghai-Tibetan Plateau, China

Article References: Zhang, Y.-C., Xiao, S., Ma, X.-Y., Chen, J.-G., Qin, Y., Liu, Y., Guo, Z.-Y., Zhou, Y.-Q., Zhao, D.-Z., Shan, Q.-S., Lu, H.-Z., & Wei, X.-X. (2026). Elymus chaobotryus (Poaceae), a new species from the north-eastern Qinghai-Tibetan Plateau, China. PhytoKeys, 279, 215-244. https://doi.org/10.3897/phytokeys.279.181697

Image Credits: AI Generated

DOI: 10.3897/phytokeys.279.181697

Keywords: Elymus, Poaceae, Qinghai-Tibetan Plateau, new species, plant taxonomy, cytogenetics, plastome phylogeny, chaobotryus, species, north-eastern, Qinghai-Tibetan, Plateau