China. Qinghai, Tongren City, Guashize Township. 35°29'11"N, 102°16'21"E, 3200 m a.s.l., 17 July 2025, leg. Yong-Chao Zhang 2019002 (holotype: HNWP 389653!).

Elymus chaobotryus resembles several Elymus species commonly occurring in the Qinghai–Tibet Plateau and northern China, particularly E. multiramosus, E. sibiricus, E. nutans and E. dahuricus var. dahuricus. These species share features such as tufted habit, erect culms, 1 or 2 spikelets per node and lanceolate glumes. Elymus chaobotryus can be readily distinguished by its unique pendulous compound spike, in which short lateral branchlets are produced from nearly all nodes of the main rachis and the lateral branches become progressively longer toward the base, giving the inflorescence a characteristic grape-like appearance.

Perennials, tufted, without rhizomes. Culms 80–130 cm tall, erect, sometimes slightly decumbent at base; leaf sheaths open to the base, glabrous; ligules almost obsolete, represented by a very short membranous rim with shortly ciliate margins; blades 17–23 × 0.2–0.5 cm, flat, linear to narrowly lanceolate, green to grey-green, surfaces smooth or nearly smooth, sometimes slightly scabrous along margins and midrib; inflorescence 16–19 cm long, a pendulous compound spike; rachis slender, scabrous on angles, without cilia, rachis nodes dilated; branches: lateral branches produced from nodes along almost the entire main rachis, from the lower part to near the apex. At each node, a single longer lateral branch (2–4 cm long, with 3–7 nodes) is typically associated with one or two shorter lateral branchlets (0.7–1.5 cm long), and/or sessile spikelets lacking branch elongation. The shorter branchlets are ascending and more or less appressed to the main axis, more numerous on the lower and middle nodes and sparser toward the apex; lateral branches become progressively longer from the apex toward the base of the inflorescence, giving a conspicuous grape-like appearance; spikelets usually 1 per branch node, occasionally 2 at the basal branch nodes, laterally compressed, containing 1–3 florets, disarticulating below the fertile florets at maturity; glumes 3–4 mm long and 0.4–0.6 mm wide, lanceolate, shorter than the first lemma, 3-veined, glabrous and scabrid along the veins, apices acute, usually bearing a mucro < 0.9 mm long; lemmas 5–7 mm long, lanceolate, awned, 3-veined (veins obscure near the base), midvein prominently raised, surfaces scabrous or sparsely puberulent toward the apex and margins; awns 3–4 mm long, slightly shorter than the lemma body, densely covered with small bristles on the surface; paleas about as long as the lemmas, keeled, ciliolate along both keels, sparsely puberulent between the keels; flowers perfect, lodicules 2, stamens 3; anthers 1.1–1.4 mm long, yellow; caryopsis narrowly rectangular-ellipsoid, 3.8–4.2 × 1.0–1.2 mm (L × W), adherent to lemma and palea; embryo 0.7–0.9 mm long; ventral sulcus narrow, shallow, linear, extending nearly the full length.

Elymus chaobotryus flowers in late August and fruits in late September.

The specific epithet chaobotryus is a compound of chao (from the given name of the collector, Yongchao Zhang) and botryus, a Latinized form of the Greek botrys (“a bunch/cluster of grapes”), referring to the branched, grape-like compound spikes bearing numerous spikelets.

Pú Suì Pī Jiǎn Cǎo (Chinese pronunciation); 葡穗披碱草 (Chinese name).

Inflorescence. Inflorescence pendulous, forming a compound spike 16–19 cm long, with 10–15 short lateral branchlets (2–4 cm long) produced from nearly all nodes of the main rachis; the lateral branches become progressively longer toward the base of the inflorescence, giving the whole spike a slightly lax, characteristic grape-like appearance. In Elymus multiramosus, the compound spike has far fewer branches (3–6 per inflorescence) and appears more compact, whereas E. sibiricus, E. nutans and E. dahuricus var. dahuricus bear simple, unbranched spikes that lack any such lateral branchlets (Table 1).

Spikelets and glumes. Spikelets usually 1 per branch node, occasionally 2 at the basal branch nodes, laterally compressed, containing 1–3 florets, disarticulating below the fertile florets at maturity. Glumes lanceolate, shorter than the first lemma, 3–4 mm long and c. 0.4–0.6 mm wide, 3-veined, glabrous but scabrid along the veins, with acute apices that usually bear a mucro less than 0.9 mm long. In Elymus multiramosus, the spikelets are also 1–2 per node, but the glumes are distinctly longer (4–7 mm) and their apical awns are much longer (1.5–2.2 mm). E. sibiricus has narrowly lanceolate glumes 4–5 mm long with 3–5 veins and a conspicuous short awn to about 4 mm, whereas in E. nutans the glumes are oblong, 3–4 mm long, 3–4-veined, with acuminate or shortly awned apices (awn 1–4 mm). E. dahuricus var. dahuricus differs even more in having lanceolate to linear-lanceolate glumes 8–10 mm long with 3–5 veins and well-developed awns about 5 mm long. Thus, the combination in E. chaobotryus of lanceolate, relatively short glumes (3–4 mm), consistently 3-veined and with mucros (< 0.9 mm) is unique among these closely related species (Table 2).

Lemmas and paleas. In Elymus chaobotryus, the lemmas are lanceolate, relatively short, 5–7 mm long, 3-veined (the veins obscure near the base), with the midvein prominently raised and the surfaces scabrous or sparsely puberulent toward the apex and along the margins; the awns arise from the lemma apex, 3–4 mm long, slightly shorter than the lemma body and densely covered with fine bristles. Paleas are about as long as the lemmas, keeled, ciliolate along both keels, sparsely puberulent between the keels, with the apex rounded or slightly flattened. In E. multiramosus the lemmas are distinctly longer (7–10 mm) but still 3-veined and bear much longer awns (9–12 mm) that clearly exceed the lemma body, while the palea apex is likewise rounded or flattened. E. sibiricus has 5-veined lemmas 8–11 mm long with awns 10–15 mm and paleas with a conspicuously 2-lobed apex; E. nutans possesses oblong-lanceolate, 5-veined lemmas about 10 mm long with awns 12–20 mm, and its paleas have obtuse-rounded or truncate apices. E. dahuricus var. dahuricus differs further in having 5-veined lemmas c. 9 mm long with long awns 10–20 mm and paleas with truncate apices. Thus, the combination in E. chaobotryus of comparatively short, 3-veined lemmas (5–7 mm) with short awns (3–4 mm), together with paleas bearing a simple rounded or flattened apex, clearly separates it from these allied species (Table 3).

Leaf sheaths and blades. In Elymus chaobotryus, the leaf sheaths are completely glabrous and the blades are flat, linear to narrowly lanceolate, 17–23 cm long and 2–5 mm wide, green to grey-green, with surfaces smooth or nearly smooth and only slightly scabrous along the margins and midrib; the ligules are almost obsolete, represented by a very short membranous rim with shortly ciliate margins. In E. multiramosus the leaf sheaths are likewise glabrous and the blades are also flat, but they are distinctly broader (18–22 cm × 5–7 mm). E. sibiricus has smooth and glabrous sheaths and flattened blades 10–20 cm long and 5–10 mm wide, while in E. nutans the blades, although flattened, are shorter and broader (6–8 cm × 3–5 mm) and often sparsely pilose above and scabrous or smooth below. E. dahuricus var. dahuricus differs even more in having smooth and glabrous sheaths and long, flattened blades 15–25 cm long and 5–12 mm wide, sometimes becoming slightly involute. Thus, among these allied species, E. chaobotryus is characterized by its combination of glabrous sheaths and conspicuously narrower, almost smooth leaf blades (2–5 mm wide) (Table 4).

Culms. Elymus chaobotryus is perennial and tufted, without rhizomes; the culms are erect, sometimes slightly decumbent at the base and 80–130 cm tall. E. multiramosus shares the tufted habit and culms that are erect with a slightly decumbent base, but the plants are generally shorter, with culm height only 82–95 cm. In E. sibiricus, the culms are solitary or sparsely tufted, erect or with the base slightly inclined and 60–90 cm tall, whereas E. nutans has tufted culms 50–70 cm tall with the bases slightly geniculate rather than decumbent. In E. dahuricus var. dahuricus and its allied varieties the culms are erect and reach 70–140 cm, but the tufts are usually more sparsely developed. Some other related species, such as E. purpuraristatus and E. dahuricus var. violeus, are much taller, with stout, erect culms up to 160–225 cm. Thus, the combination in E. chaobotryus of a tufted, non-rhizomatous habit with culms erect, only slightly decumbent at the base and of intermediate height (80–130 cm) distinguishes it from both the shorter, weakly tufted species and the markedly taller robust species in the complex (Table 5).

The species is presently known only from a small area in Guashize Township, Tongren City, southeastern Qinghai Province (35°29'11"N, 102°16'21"E), on the north-eastern Qinghai-Tibetan Plateau.

Field surveys documented seven local populations totaling ca. 36 individuals. Individuals were strongly tufted and typically produced more than 30 tillers. All observed plants bore the distinctive pendulous compound spike, with short lateral branchlets present along most nodes of the main rachis.

Elymus chaobotryus was discovered in the corner of the walled courtyard of a herder’s house, at an elevation of 3200 m a.s.l., and 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.

Other plant species in the vicinity include Carex parvula O. Yano, Carex alatauensis S. R. Zhang, Carex capillifolia (Decne.) S. R. Zhang, Elymus dahuricus Turcz., Dasiphora fruticosa (L.) Rydb., Poa araratica Trautv., Festuca sinensis Keng ex E. B. Alexeev.

The taxon was first noticed in the field in 2019, when seeds were collected. Since 2020, plants raised from these seeds have been grown continuously in a forage germplasm nursery near Qinghai Lake on the Qinghai-Tibet Plateau (ca. 3200 m a.s.l.). Across multiple years of cultivation, the diagnostic inflorescence architecture (a pendulous compound spike with lateral branchlets, producing a grape-like outline) has remained stable, and a seed stock has been built up. In 2025, replicated field plots were established in Haibei Tibetan Autonomous Prefecture (three counties; three replicates per county; 3 × 5 m per plot) using a sowing rate of 22.5 kg ha^–1. The diagnostic inflorescence architecture remained stable in both nursery-grown and field-grown plants (Suppl. material 1).

None of the examined specimens of E. dahuricus or the other surveyed Elymus taxa possessed the compound-spike architecture observed in E. chaobotryus (Suppl. material 3: table SS2). Several specimens showed lax, flexuous, pendulous, or superficially branched-looking spikes; however, in all such cases the inflorescence retained a single continuous main rachis and lacked lateral spike-bearing branchlets and secondary rachises. The apparent branching was associated with loose spikelet arrangement, spreading awns, overlapping culms or spikes, leaf obstruction, or specimen pressing. Accordingly, no surveyed specimen showed the hierarchical compound-spike organisation characteristic of E. chaobotryus.

Flow-cytometric analysis yielded estimated genome sizes of 11.43 Gb for Elymus chaobotryus, 11.32 Gb for E. multiramosus, and 7.10 Gb for E. sibiricus (Table 6). Based on relative fluorescence intensity and genome-size comparison among the Elymus samples, E. chaobotryus and E. multiramosus were inferred to be hexaploid (6x), whereas E. sibiricus was inferred to be tetraploid (4x).

Chromosome counts from DAPI-stained metaphase cells showed that the examined Elymus chaobotryus sample had 2n = 42 chromosomes (Fig. 9A). The chromosomes were approximately 5.0–8.0 μm long and were predominantly metacentric to submetacentric. Genomic in situ hybridization (GISH) using total genomic DNA of Pseudoroegneria spicata as a probe identified 14 St-genome chromosomes (Fig. 9B). Sequential FISH with Oligo-HvCSR and Oligo-pTa535 revealed distinct hybridization patterns among the remaining chromosomes, allowing them to be assigned to two groups interpreted as representing the H and Y genomes, with 14 chromosomes in each group (Fig. 9C). Together, these results support a hexaploid chromosome complement (2n = 6x = 42) in E. chaobotryus and are consistent with an StHY genomic constitution.