Rodriguez, Saarela & Peterson & Valdés-Reyna, 2014

Saarela, Jeffery M., Peterson, Paul M. & Valdés-Reyna, Jesus, 2014, A taxonomic revision of Bromus (Poaceae: Pooideae: Bromeae) in México and Central America, Phytotaxa 185 (1), pp. 1-147 : 68-72

7. Bromus densus Swallen (1950: 396) . Figs. 25–27 .

Type:— MÉXICO. Nuevo León: Mpio. Zaragoza, Cerro del Viejo, 15 mi W Dulces Nombres , in open pine forest, alt. 3330 m, densely tufted perennial to 3.5 ft tall, 18 August 1948, F. G . Meyer & D. J . Rogers 2976 (holotype US-1962994 !, isotypes G-00099281!, MO-1599222 !, P-00689802 !) .

Plants perennial, densely caespitose, not rhizomatous. Culms 40–110 cm tall, with a thick, robust base 3–4 mm wide, glabrous or scabrous below inflorescences; nodes 3–4, glabrous. Leaf sheaths glabrous, margins sparsely to densely pilose distally and at collar, hairs up to 4 mm long; auricles usually absent, occassionally present; ligules 0.5–1 mm long, glabrous; blades up to 74 cm × 2–3 mm, flat, pilose proximally, hairs up to 4 mm long, adaxial and abaxial surfaces glabrous, margins serrulate. Panicles 7–22.5 cm × 3.5–4.5 cm, open, nodding, branches ascending, 0.4–10 cm long, shorter or longer than spikelets, scabrous, 1–4 spikelets per branch. Spikelets (1.5–) 2–3.5 cm long, 5–7-flowered, elliptic to lanceolate, terete to moderately laterally compressed, rachillas sometimes visible at maturity; glumes glabrous, margins hyaline, midnerves glabrous or scabrous; lower glumes 6.5–12 mm × 0.5–1 mm, lanceolate, 1-nerved, purplish-green along the nerve, apices acute; upper glumes 8–13 mm × (0.8–) 1–1.3 mm, lanceolate, 3-nerved, purplish-green along the nerves, usually lighter in color between nerves and ± translucent, apices acute to obtuse. Lemmas 10–14 mm × 1–2 mm, elliptic to lanceolate, rounded over the back, apices acute to obtuse, usually minutely bifid, 3-nerved, purplish-green along nerves, usually lighter in color between nerves and ± translucent, glabrous to scabrous, sometimes minutely pubescent along margins proximally, awns (1–) 2–3.5 mm long, arising 0–0.5 mm below lemma apex, straight; paleas 9–11 mm long, backs glabrous to scabridulous, keels ciliate, cilia up to 0.2 mm long; anthers 6–6.5 mm long; caryopses 6−9 mm long, light brown. 2 n = unknown.

Distribution:―Native. Bromus densus is endemic to Mexico in the central Sierra Madre Oriental in Coahuila (Sierra de Zapalinamé), Nuevo León (Cerro Potosí), San Luis Potosí (Cerro de la Luz) and Tamaulipas (Peña Nevada) ( Fig. 28 ).

Ecology:— This species is found on gentle to steep rocky slopes and cliffs, primarily in calcareous soils; associated with Quercus greggii Candolle (1864: 34) Trel. in Standley (1922: 185), Q. emoryi , Pinus greggii Engelm. ex Parlatore (1868: 3) , Pseudotsuga menziesii , Cupressus arizonica , Abies vejarii , Symphoricarpos Duhamel du Monceau (1755: 295) , Pachistima myrsinites Rafinesque (1838: 42) , Ceanothus , Thalictrum Linnaeus

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(1753: 545), Lupinus Linnaeus (1753: 721) , Penstemon barbatus ( Cavanilles 1795: 22) Roth (1806: 49) , Cercocarpus montanus , Campanula rotundifolia Linnaeus (1753: 163) , Trisetum viride (Kunth in Humboldt 1816: 147) Kunth (1829) and Buddleja Linnaeus (1753: 112) . Elevation: 2700–3380 m.

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Common Name: ―Bromo del infiernio ( Saulés & Dávila Aranda 1992) (Spanish).

Comments: ― Bromus densus is one of three Mexican species characterized by 3-nerved lemmas. It is here newly recognized in sect. Mexibromus , along with B. attenuatus and B. dolichocarpus . This is the first report of the species from San Luis Potosí, where we collected it in 2010 on Cerro de la Luz. This is a 255 km range extension to the south. The species is used as fodder ( Saulés & Dávila Aranda 1992).

Specimens Examined:― MÉXICO. Coahuila: Sierra de Zapalinamé , área protegida, El Penitente, 25.3454°N, 100.9008°W, 3123 m, 29 September 2007, S. G . Gómez P., P. M . Peterson & J. M . Saarela 593 ( ANSM); Sierra de Zapalinamé, brecha cortafuegos Chapultepec, al sureste de Saltillo , 25.2633°N, 100.6389°W, 28 August 2008, E. F . Álvarez G . 313 ( ANSM); Sierra de Zapalinamé, El Penitente , 25.3454°N, 100.9008°W, 3123 m, 29 September 2007, S. G . Gómez 590, P. M . Peterson & J. M . Saarela ( ANSM); Sierra de Zapalinamé , along trail from El Cuatro to El Penitente, 25.3494°N, 100.90511°W, 2925 m, 28 September 2007, P. M . Peterson, J. M . Saarela & S. G . Gómez Pérez 21128 ( CAN, MO, US); Sierra de Zapalinamé , [25.3468°N, 100.9016°W], 2940 m, 19 May 1990, G. B . Hinton 20284 ( GH); Sierra de Zapalinamé , 25.3468°N, 100.908°W, 2800 m, 20 September 2003, P. M . Peterson, J . Valdés-Reyna & R. H . Cárdenas 17870 ( CAN, US); Sierra de Zapalinamé , Eof Saltillo, 25.3468°N, 100.9016°W, 2700 m, 2 September 2005, P. M . Peterson & J . Valdés-Reyna 18786 ( US) & 18789 ( US); 40 mi Sof Saltillo , July 1880, E . Palmer 1372 ( GH, mixed sheet with B. anomalus, NY ); Sierra la Viga , 6 km al de Jamé, Puerto Maravillas, 25.3667°N, 100.9553°W, 3000–3150 m, 16 September 1989, J. A . Villarreal, P . Hooge, J . Valdés-Reyna & M . Barkworth VR-1984 ( NY); La Siberia, Sierra de la Marta, cerca del Ejido Sta. Rita ca. 18 km al SE de San Antonio de las Alazanas, 25.2333°N, 100.4167°W, 22 July 1983, J . Valdés-Reyna & L. E . Rodriguez G. s.n. ( ARIZ-284698 ) . Nuevo León: along road up to Cerro Potosí, 24.8875°N, 100.21°W, 2884 m, 21 October 2007, P. M . Peterson, J. M . Saarela & D. Stancik 21453 ( CAN, US); Cerro El Potosí, localizado en Galeana , 24.82°N, 100.07°W, 2950 m, 15 August 1998, J . Garza C. & M . Castillo B . 210 ( MEXU-1089779 ); Cerro Potosí, near microwave tower, 24.8667°N, 100.2167°W, 2743 m, 8 July 1963, R. L . McGregor, L. J . Harms, A. J . Robinson, R . del Rosario & R . Segal 299 ( NY, US-2454944 ); Sierra Madre Oriental, ascent to Sierra Infernillo , ca. 15 mi SW of Galeana, 24.61°N, 100.01°W, 9000–10000 ft, 16 June 1934, C. H . Mueller & M. T . Mueller 811 ( GH, F-938711, MICH-1119215 ); Sierra Madre Oriental , 11.4 mi Wof Dieciocho de Marzo up road towards Cerro Potosi, 3130 m, 18 October 1995, P. M . Peterson & M. B . Knowles 13334 ( US) . San Luis Potosí: Cerro de la Luz, Wof La Trinidad ,

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21.40792°N, 99.1023°W, 2300–2688 m, 23 September 2010, P. M. Peterson, J. M. Saarela & K. Romanschenko 23580 ( US). Tamaulipas: Mpio. Miquihuana, Col. Agr. La Peña , 23.63°N, 99.73°W, 2900 m, 9 June 1982, G. Villegas 489b ( MEXU); on Eand Sslopes and summit of Peña Nevada , 23.7°N, 99.8°W, 19 July 1949, L. R. Stanford, S. M. Lauber & L. A. Taylor 2574 ( NY, RSA-POM-72563 , US-2013060 ) .

Figures

FIGURE 25. Bromus densus. A. Lemma. B. Spikelet. C. Ligule. D. Habit. Based on Peterson et al. 17870 (CAN). Illustration by Paulette Dennis © Paulette Dennis.

FIGURE 26. Bromus densus. Mueller & Mueller 811 (MICH-1119215).

FIGURE 27. A large population of Bromus densus growing on grassy slopes in Sierra Zapaliname, Coahuila, México (Peterson et al. 21128). Photo: J.M. Saarela.

FIGURE 28. Geographical distribution of Bromus densus in México.