Achnatherum pilosum Z.S. Zhang & W.L. Chen, 2018

Achnatherum pilosum Z.S. Zhang & W.L. Chen View in CoL , sp. nov. ( Fig.s. 1–2 View FIGURE 1 View FIGURE 2 )

Achnatherum pilosum View in CoL resembles A. inebrians ( Hance 1876: 212) Keng ex Tzvelev (1968: 40) View in CoL , A. psilantherum Keng ex Tzvelev (1968: 41) , A. inaequiglume Keng (1976: 151 , 443), and A. saposhnikovii ( Roshevitz 1916: 174) Nevski (1937: 224) View in CoL by having ligules truncate, panicles contracted or loosely contracted, lemmas similar in length ( 2.5–4.5 mm long), and calluses 0.2–0.3 mm long, bearded. It differs from them by the combination of panicles loosely contracted; glumes subequal, 5.5–7 mm long; lemmas 2.8–3.2 mm long, evenly pubescent with some slightly long hairs (ca. 0.6 mm long) at the apex; awns 1 - or inconspicuously 2 - geniculate, 0.9–1.5 cm long, scabrous, with twisted columns; and anthers 1.5–1.8 mm long, bearded at the apex.

Type: — CHINA. Sichuan: Dêgê, Chola Shan, alt. 3200 m, 31.82°N, 98.58°E, 14 September 2017, Zhang 2379 ( holotype PE!).

Plants tightly cespitose, not rhizomatous, basal branching extravaginal. Culms erect, glabrous, 40–80 cm tall, 0.5–1.3 mm diam., with approx. 3 nodes. Leaves basal, except in the flowering culms; leaf sheaths glabrous, shorter than the internodes; ligules 0.1–0.9 mm long, truncate, often toothed; leaf blades 8–23 cm × 0.3–3 mm, filiform, flat or folded. Panicles 7–11 × ca. 1 cm, loosely contracted, narrowly oblong or linear; branches 2 to 4 per node, suberect or slightly spreading, up to 4 cm long. Spikelets 5.5–7 mm long, yellowish - brown or purple and hyaline towards the apex; glumes subequal or the lower glume slightly longer than the upper glume by 1 mm, lanceolate, 3 - veined, apex acute to acuminate; floret fusiform; lemma 2.8–3.2 mm long, evenly pubescent on the back, hairs ca. 0.6 mm at the apex and ca. 0.5 mm long below, apex with two lobes ca. 0.1 mm long; awn 0.9–1.5 cm long, persistent, 1 - or inconspicuously 2 - geniculate, scabrid, column twisted; callus ca. 0.3 mm long, subacute; palea slightly shorter than the lemma; anthers three, 1.5–1.8 mm long, bearded at the apex. Caryopsis 2.5–3 mm long, obovate, distal portion slightly exposed between gaping lemma and palea or concealed by floret at maturity.

Etymology: —The specific epithet ‘pilosum’, from the Latin word ‘pilus’ ( Clifford & Bostock 2007), refers to the anthers bearded at the apex. Chinese name: ḂIȐȐḍ.

Comments: —The new species was included in Achnatherum because of the fusiform spikelets ( Fig. 1C–D View FIGURE 1 , 2D View FIGURE 2 ); subacute calluses; lemmas with non - overlapping margins ( Fig. 1F, G View FIGURE 1 ); and awns persistent, twisted, 1 - or inconspicuously 2 - geniculate ( Fig. 1D View FIGURE 1 , 2D, I View FIGURE 2 ), which are the diagnostic features of this genus ( Romaschenko et al. 2012, Kellogg 2015). In addition, its placement in Achnatherum is also supported by the maize - like lemma epidermal pattern ( Fig. 2S View FIGURE 2 ) and chromosome number 2 n = 24 ( Fig. 2T View FIGURE 2 ) ( Romaschenko et al. 2012, Kellogg 2015).

Achnatherum pilosum is morphologically similar to A. inaequiglume , A. inebrians , A. psilantherum , and A. saposhnikovii , which have truncate ligules, contracted panicles ( Fig 2C View FIGURE 2 ), lemmas similar in length ( 2.5–4.5 mm long; Fig 2D–M View FIGURE 2 ), and calluses 2–3 mm long, bearded ( Fig 2I–M View FIGURE 2 ) ( Hooker 1896, Bor 1960, Tzvelev 1976, Freitag 1985, Noltie & Garden 2000, Wu & Phillips 2006). Achnatherum inaequiglume and A. saposhnikovii differ from A. pilosum due to their straight, not twisted awns, and anthers glabrous at the apex ( Fig. 2E, J, O and H, M, R View FIGURE 2 respectively), whereas the new species presents 1(–2)-geniculate, twisted awns, and anthers bearded at the apex ( Fig. 2D, I, N View FIGURE 2 ). The former presents unequal glumes ( Fig. 2E View FIGURE 2 ), long awns ( 1.5–2 cm long) and long hairs ( 3–4 mm long) at the apex of the lemma ( Fig. 2E, J View FIGURE 2 ), whereas the second presents subequal glumes ( Fig. 2H View FIGURE 2 ), short awns ( 0.4 cm long) and lemmas evenly pubescent ( Fig. 2H, M View FIGURE 2 ). The new species differs from A. inebrians by the loosely contracted panicles ( Fig. 2C View FIGURE 2 ), short lemmas ( 2.8–3.1 mm long), shorter hairs at the apex of the lemmas (ca. 0.6 mm long), long awns ( 0.9–1.5 cm long) and shorter anthers ( 1.5–1.8 mm long). The new species differs from A. psilantherum by its short glumes ( 5.5–7 mm long), lemmas ( 2.8–3.1 mm long), awns ( 0.9–1.5 cm long), and short anthers ( 1.5–1.8 mm long) with a cluster of beard at the apex ( Fig. 2N View FIGURE 2 ). Morphological differences among A. pilosum and relatives are summarized in Table 1.

Distribution and habitat: — Achnatherum pilosum grows in forest fringes, grassy mountain slopes and wet river banks ( Fig. 2A–B View FIGURE 2 ). It is endemic to China, restricted to Sichuan and Qinghai provinces ( Fig. 3 View FIGURE 3 ). Achnatherum inebrians is widely distributed in Qinghai - Tibet plateau and central Asia ( Tzvelev 1976, Wu & Phillips 2006). Achnatherum inaequiglume and A. psilantherum occur in the northeast and adjacent areas of Qinghai-Tibet plateau and their distribution area do not overlap with that of the new species ( Tzvelev 1976, Wu & Phillips 2006). Achnatherum saposhnikovii is distributed in central Asia, which is also geographically isolated from the new species ( Tzvelev 1976, Wu & Phillips 2006).

Lemma epidermal pattern: — Achnatherum pilosum presents a MLP, typical of Achnatherum s.s. ( Romaschenko et al. 2012). The FC are thin - walled, approximately equal in length and width to significantly shorter than wide ( Fig. 2S View FIGURE 2 ). The FC are square - round, or longitudinally compressed ( Fig. 2S View FIGURE 2 ). Oval silica bodies regularly alternate with FC ( Fig. 2S View FIGURE 2 ). Lemma surface resembles the surface of a fruiting inflorescence of maize ( Fig. 2S View FIGURE 2 ). Cork cells are absent. Macrohairs are present ( Fig. 2S View FIGURE 2 ).

Cytology: —The diploid chromosome number of Achnatherum pilosum is 2n = 24 ( Fig. 2T View FIGURE 2 ), as well as that of A. calamagrostis ( Linnaeus 1759: 872) Palisot de Beauvois (1812: 146) , type species of Achnatherum , and most species of Achnatherum s.s. ( Tzvelev 1976, Martinovský 1980, Vázquez & Devesa 1996, Romaschenko et al. 2012).

Additional specimens examined ( paratypes): — CHINA. Qinghai: Nangqên , 3650 m, 32.32°N, 96.47°E, 4 September 1996, Ho, et al. 2898 ( PE!) GoogleMaps ; Chindu xian, 3700 m, 32.98°N, 97.35°E, 15 August 1996, Ho, et al. 1828 ( PE!) GoogleMaps .