Bromus attenuatus Swallen 1950
Creators: name: Saarela, Jeffery M.
name: Peterson, Paul M.
name: Valdés-Reyna, Jesus
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy

description: 3. Bromus attenuatus Swallen (1950: 397). Figs. 8, 9.
Type:— MÉXICO. Nuevo León: Dulces Nombres, and just Eof border into Tamaulipas, 24ºN, 99º30'– 100º30'W, alt. 1900 m, in rich humus on ledges above dry stream course in canyon on Eside of Cerro Linadero, 11 August 1948, F. G. Meyer & D. J. Rogers 2937 (holotype US-1962991!, isotypes E-00373825!, G-00099283!, MO-1598493!, P-03630120!).
Plants perennial, not rhizomatous. Culms up to 150 cm tall, (1–) 2–3 mm wide at base, erect or ascending, bases sometimes decumbent, glabrous below inflorescences; nodes 2–4, glabrous or sparsely pubescent. Leaf sheaths glabrous or pubescent, hairs up to 0.2 mm long; auricles present; ligules 0.4–0.6 mm long, glabrous, sometimes with a ring of pilose hairs arising at the base of the blade beneath and above the ligule; blades up to 60 cm × 4–16 mm, conduplicate to involute proximally, flat distally, attenuate, gradually narrowed to the base, adaxial surfaces glabrous between the nerves, pubescent on the nerves, hairs up to 0.5 mm long, abaxial surfaces moderately to densely scabrous on and between the nerves, margins serrulate. Panicles 15.5–24 cm long, open, nodding, branches erect to spreading, scabrous, 1–2(–3) spikelets per branch. Spikelets 2–3 cm long, 6–8-flowered, linear-lanceolate, terete to moderately laterally compressed; glumes glabrous, margins hyaline, miderves glabrous to scabrous distally; lower glumes 6.5–9.8 mm long, lanceolate, 1-nerved, green along the nerve, apices acute; upper glumes 8.6–11 mm long, obovate-lanceolate, 3-nerved, green along the nerves, light green-translucent between the nerves, apices obtuse or acute to mucronate, mucros up to 1 mm long; lemmas 11–14 mm long, linear-lanceolate, rounded over the back, apices acute, 3-nerved, the nerves strong, glabrous, green along the nerves, light green-translucent between the nerves, nerves glabrous to scabrous distally; awns 2.5–4.5(–5) mm long, inserted up to 0.5 mm below lemma apex, straight; paleas shorter and narrower than lemmas, backs glabrous or puberulent, keels glabrous or ciliate, cilia up to 0.1 mm long; anthers 3.5–5.5 mm long; caryopses 9−10 mm long. 2 n = unknown.
Distribution: ― Native. Bromus attenuatus is endemic to the southern Sierra Madre Oriental in northeastern México, in Nuevo León, Tamaulipas, San Luis Potosí and northwestern Hidalgo (Fig. 10).
Ecology: —The species grows on rocky to gentle slopes in pine-oak forests, often on calcareous soils; associated with Liquidambar styraciflura Linnaeus (1753: 999), Juniperus flaccida Schlechtendal (1838: 495), Carya Nuttall (1818: 220), Arbutus xalapensis, Pinus pseudostrobus Lindley (1839: Misc. 63), Picea martinezii Patterson (1988: 131), Abies vejari Martínez (1942a: 629), Tilia Linnaeus (1753: 514), Ulmus Linnaeus (1753:
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225), Triniochloa stipoides (Kunth in Humboldt et al. 1815 [1816]: 131) Hitchcock (1913: 303), Polypodium Linnaeus (1753: 1082), Adiantum Linnaeus (1753: 1094), Cornus stolonifera Michaux (1803a: 92) and Quercus Linnaeus (1753: 994) spp. Elevation: 1809–2250 m.
ATAXONOMIC REVISION OF BROMUS (POACEAE)
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Comments: ―This is the first report of the species from San Luis Potosí, where we collected it in 2010 on Cerro de la Luz. There is a large gap in distribution between the San Luis Potosí and Hidalgo populations to the south and the Nuevo León populations to the north.
Bromus attenuatus is one of three Mexican species with three-nerved lemmas. It is easily distinguished from B. dolichocarpus by its glabrous lemmas, shorter awns and wider leaf blades that narrow towards their bases, and from B. densus by its longer awns, shorter anthers and wider leaf blades that narrow towards their bases. Wagnon (1952) and Soderstrom & Beaman (1968) suggested that B. attenuatus is probably more closely related to B. dolichocarpus than it is to B. densus. Accordingly, in a molecular phylogenetic study, Saarela et al. (2007) found B. attenuatus and B. dolichocarpus to be closely-related and comprise a unique lineage in Bromus, which is here newly recognized as sect. Mexibromus. Bromus attenuatus and B. dolichocarpus have stronger lemma nerves than B. densus.
The epithet attenuatus refers to the morphology of the leaf blades; blades that narrow distinctly at both ends do not occur in any other Bromus species in North America.
Specimens Examined:― MÉXICO. Hidalgo: Barranca de San Vicente near km 238 on highway between Zimapan and Jacala, [20.87°N, 99.28°W], 1800–2000 m, 24 September 1949, H. E. Moore, Jr. 5066 (MEXU- 143525, MICH-1119164). Nuevo León: Sof Zaragoza on road towards Ejido La Encantada, 23.9276°N, 99.7978°W, 2171 m, 21 September 2002, P. M. Peterson, J. Valdés-Reyna & M. Sosa Morales 16759 (ANSM, CAN, MO, US) & 16762 (ANSM, CAN, US); Sierra La Lagunita, 13.5 mi SE of Aramberri on road towards Agua Fría, 24.0417°N, 99.7333°W, 2250 m, 20 September 2002, P. M. Peterson, J. Valdés-Reyna & M. Sosa Morales 16722 (CAN, US); Sierra La Lagunita, 13.5 mi SE of Aramberri on road towards Agua Fría, 24.0423°N, 99.7345°W, 2170 m, 20 September 2002, P. M. Peterson, J. Valdés-Reyna & M. Sosa Morales 16717 (ANSM, CAN, MO, US). San Luis Potosí: 1.3 km Wof La Trinidad, 21.40494°N, 99.0816°W, 2200 m, 23 September 2010, P. M. Peterson, J. M. Saarela & K. Romaschenko 23558 (US); Cerro de la Luz, Wof La Trinidad, 21.40792°N, 99.1023°W, 2300–2688 m, 23 September 2010, P. M. Peterson, J. M. Saarela & K. Romaschenko 23574 (US). Tamaulipas: Sierra Las Cautivas, 21 mi Wof Ejido Guayabas on road to Dulces Nombres, 23.9871°N, 99.48°W, 1830 m, 25 September 2007, P. M. Peterson & J. M. Saarela 21060 (CAN, MO, US); 13.8 mi NE of Dulces Nombres, 23.9866°N, 99.48°W, 1809 m, 23 September 2001, P. M. Peterson & J. Valdés-Reyna 15926 (CAN, MO, US).
description: Published as part of Saarela, Jeffery M., Peterson, Paul M. & Valdés-Reyna, Jesus, 2014, A taxonomic revision of Bromus (Poaceae: Pooideae: Bromeae) in México and Central America, pp. 1-147 in Phytotaxa 185 (1) on pages 28-31, DOI: 10.11646/phytotaxa.185.1.1, http://zenodo.org/record/10090001