Chusquea septentrionalis emend. Ruiz-Sanchez, Art. Castro & Clark

Ruiz-Sanchez, Eduardo, Castro-Castro, Arturo & Clark, Lynn G., 2022, A new informal group in Chusquea subg. Swallenochloa (Poaceae: Bambusoideae: Bambuseae) and emended descriptions for the Mexican endemics C. enigmatica and C. septentrionalis, Phytotaxa 554 (1), pp. 47-58 : 51-55

Chusquea septentrionalis emend. Ruiz-Sanchez, Art. Castro & Clark

TYPE:— MEXICO. Durango. Municipality Pueblo Nuevo: Santa Bárbara, Santa Bárbara State Park to the end of the interpretative trail, 3 km from the bifurcation to the Puentecillas State Park , 2724 m, 15 Dec 2015 (sterile), A. Castro-Castro and J. G. González-Gallegos 4241 (holotype: CIIDIR!; isotypes: IBUG!, ISC!, MEXU!) .

Description:—Rhizomes pachymorph, short-necked. Culms 1.5–3.0 m tall, 10–20 mm in basal diameter, erect, somewhat arching toward the apices. Internodes 80–170 mm long, 15–36 per culm, terete, glabrous, green to dark green purple, hollow, the walls 3–5 mm thick, the lacuna occupying 50% of the total diameter. Culm leaves 100–190 mm long, extending along the whole internode and overlapping the next node, persistent and disintegrating on the culm, glabrous; sheaths 90–140 mm long, rectangular with a strongly convex apex, 3.3–9.0 times as long as the blade, with margins ciliolate from white cilia; blades 10–42 mm long, triangular, erect, persistent, short mucronate at apex, with margins finely ciliate, abaxially and adaxially glabrous becoming adaxially sparsely pubescent toward the apex; girdle absent; inner ligule ca. 0.05 mm long, ciliate. Nodes at mid culm with the central bud slightly larger than the subsidiaries, triangular; subsidiary buds 3–6 per complement, axillary, closely adjacent and linearly arranged in 1 row, with the base of the buds arising about 2 mm above the nodal line; prophylls with ciliate margins; nodal line more or less horizontal, supranodal ridge present and prominent. Branching intravaginal; 3–6 branches per node, growing almost parallel to the main culm, 130–400 mm long, 1–2 mm in diameter, rebranching (second order) and developing a single branch. Foliage leaves 3–9 per complement; sheaths glabrous, with entire margin; blades 90–165 mm long, 5–12 mm wide, L:W 13–21; blades adaxially and abaxially strongly tessellate, glabrous, attenuate at base, subulate at apex, with finely scabrous margin; pseudopetioles 1.5–3.0 mm long, adaxially and abaxially glabrous; inner ligules 5–10 mm long, well developed, clasping the branch, abaxially glabrous; outer ligule a ciliate irregular rim 0.2–1.0 mm long. Synflorescences 45–90 mm long, 1–15 mm wide, narrow, somewhat congested, not fully exserted from the subtending sheath; rachis slightly sinuate, angular, slightly scabrous; branches appressed, but not strongly so, ascending, 10–20 mm long, angular, scabrous; pedicels 1–5(–7) mm long, angular, scabrous. Spikelets (6.2–)7.2–8.8(–10.8) mm long, 1–1.3 mm wide, glabrous, laterally compressed. Glumes I and II ovate, obtuse, glabrous, enervate; glume I (0.2–)0.6– 1(–1.4) mm long, 1/50–1/5 the spikelet length; glume II 0.6–1.2 mm long, 1/15–1/4 the spikelet length. Glumes III and IV scabrous, awned, margin entire, ciliate to the apex; glume III including the awn (4.4–)4.6–6.8(–7.2) mm long, 5-nerved, the awn (0.6–) 1.2–2.2 mm, 1/4–3/4 the spikelet length; glume IV including the awn (5.6–)5.8–7.8(–8.2) mm long, 3–4-nerved, the awn 0.6–1.2 mm long, 1/2–9/10 the spikelet length, 4–5-nerved. Lemmas (6–) 8–9 mm long, 7–nerved, green, scabrous, awned, margin ciliate toward the apex; awn 0.6–0.8 mm long, 5-nerved. Paleas (6–) 8–9 mm long, 2–nerved, scabrous; nerves scabrous, apex biapiculate, the sulcus scabrous. Lodicules 3, membranaceous, 0.6–0.8 mm long, glabrous, hyaline, margin entire, apex truncate. Stamens and stigmas not seen. Fruit not seen ( Fig. 4 ).

Habitat and distribution:— Chusquea septentrionalis was described from Durango state, known from three localities ( Ruiz-Sanchez et al. 2017). This species inhabits coniferous forest growing from 2333–2729 m (including elevation data from the new records first reported here). We recorded the presence of this species far north (25°39’49.17’’N, 107°0’25.44’’W) in Sinaloa state from the type locality ( Fig. 2 , 5 ), making this species unquestionably the northernmost of the genus .

Comparison:—Synflorescences and spikelets of C. septentrionalis are more similar to C. bilimekii than to C. perotensis ( Table 2 ). Synflorescences are congested-paniculate in C. septentrionalis and C. bilimekii and openpaniculate in C. perotensis . Further comparisons will be between C. septentrionalis and C. bilimekii . Glumes I and II are glabrous in C. septentrionalis and abaxially pubescent in C. bilimekii . Glumes III and IV are abaxially scabrous in C. septentrionalis and pubescent in C. bilimekii . Glumes III and IV are awned in C. septentrionalis , but are subulate and apiculate in C. bilimekii . Lemmas are shorter (6–) 8–9 mm and abaxially scabrous in C. septentrionalis , and these are longer (9.6–10.1 mm) and pubescent in C. bilimekii ( Table 2 ).

Etymology:—The specific epithet refers to this species having the northernmost distribution among the members of Chusquea subg. Swallenochloa .

Phenology:—The first known flowering record for this species was collected during the summer of 2019 (A. Castro-Castro et al. 4600). All flowers examined from this specimen, however, were past mature and had no fruits.

Specimens examined:— Durango: Durango municipality, Salto del Agua Llovida, km 58 de la brecha Navios-El Regocijo-San Isidro-Molinillos , a partir del km 72 de la carretera Méx. 40 Durango-Mazatlán , 23°32’15.6’’N, 104°15’15.5’’W, 2333 m, 10 julio 2019, (fl), A. Castro-Castro et al. 4600 (CIIDIR, IBUG); Pueblo Nuevo, La Ciudad, Parque Ecoturístico Mexiquillo, alrededores de la cascada, 23°42’5’’N, 105°40’14.9’’W, 2551 m elevación, 8 agosto 2019, A. Castro-Castro et al. 4497 (CIIDIR); parque la Pirámide, camino en cañada, paralelo al primer túnel, carretera Durango-Mazatlán, 23°43’5.09’’N, 105°31’2.39’’W, 2729 m, 27 agosto 2021, S.E. Centeno & R. Machado 152 (CIIDIR) . Sinaloa: Badiraguato, Santa Gertrudis, camino a Santa Gertrudis-Alisitos-La Herradura , 25°39’49.17’’N, 107°0’25.44’’W, 2560 m elevación, 1 noviembre 2020, E.I. Rojas-Aguilar & M.A. González-Bernal 398a (CIIDIR, IBUG) .

Figures

FIGURE 2. Geographical distribution map of Chusquea enigmatica and C. septentrionalis. Black squares belong to C. enigmatica, black triangles are localities of C. septentrionalis. Black arrows indicate the type locality for each species. Dotted line indicates previous northernmost Chusquea collections.

FIGURE 4. Chusquea septentrionalis. A. Synflorescence. B. Flowering branch showing persistent lower glumes. C. Spikelet. D. Lower glumes (I, II). E. Upper glumes (III, IV). F. Lemma (right) and palea (left). Based on A. Castro-Castro et al. 4600. Illustration by Juvenal Aragón Parada.

FIGURE 5. Chusquea spetentrionalis. A–C. Flowering clumps from Durango (A, C) and Sinaloa (B). D. Flowering branches showing synflorescences. E. Synflorescence showing spikelets. Photos by Arturo Castro-Castro.