Bromus arizonicus (Shear) Stebbins

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 : 24-28

2. Bromus arizonicus (Shear) Stebbins in Stebbins et al. (1944: 309). Figs. 5 , 6 .

Basionym: Bromus carinatus var. arizonicus Shear (1900: 62) . Ceratochloa arizonica (Shear) Holub (1973: 170) . Type:— UNITED STATES OF AMERICA. Arizona: Pima Co., Tucson, Santa Cruz Valley, 3 May 1884, C.G. Pringle s.n. (holotype US-81568!, isotypes GH-00023238!, MIN-1000471!, PH-01038760!, PH-01050337!).

Plants annual, tufted. Culms (8–) 30–90 cm tall, (1–) 1.5–2 mm wide at base, erect, glabrous below inflorescences; nodes 2–4, glabrous or weakly pubescent. Leaf sheaths puberulent to pubescent, hairs up to 1 mm long; ligules

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1–2.1(–3) mm long; auricles absent; blades up to 30 cm × (1.5–) 2–6 mm, flat, abaxial and adaxial surfaces pilose, sometimes glabrous, hairs up to 0.6 mm long, margins serrulate. Panicles (3–) 5–30 cm × 1–2(–3) cm, erect, ± contracted, at least when young, branches erect to ascending, scabrous, often shorter than spikelets, 1–2 spikelets per branch. Spikelets 1.5–2.5(–2.7) cm long, 4–9-flowered, elliptic to lanceolate, strongly laterally compressed; glumes glabrous or scabrous, margins hyaline, midnerves glabrous proximally, scabrous distally, apices acute; lower glumes (6–) 8–13 mm long, lanceolate, 3–5-nerved, green to purplish-green along and between nerves; upper glumes (7–) 9–15 mm long, ± equal in length to the lowest lemma, ovate-lanceolate, 5–9-nerved, green to purplishgreen along and between the nerves; lemmas 9.5–14 mm long, lanceolate, strongly keeled, apices acute, margins usually weakly to moderately pubescent throughout or distally, sometimes scabrous to short-pubescent, hairs up to 0.5 mm long, backs glabrous, scabrous or pubescent, hairs usually shorter than those along margins, midnerves glabrous to scabrous distally, margins hyaline; awns (4–) 7–15 mm long, inserted up to 0.5(–0.6) mm below the lemma apex, straight; paleas shorter and narrower than lemmas, backs glabrous, keels ciliate, cilia up to 0.1 mm long; anthers 0.4–0.5 mm long; caryopses 8−9.5 mm long. 2 n = 84 ( Stebbins et al. 1944, Klos et al. 2009).

Distribution:―Native. In México this species is known only from Baja California and Sonora ( Fig. 7 ). Its range includes California, southwest Nevada and New México ( Pavlick & Anderton 2007). There are numerous collections of B. arizonicus on the border of Sonora and Arizona (R. Felger, pers. comm. 2014). Its distribution in Sonora is likely broader than shown here. In addition to Baja California and Sonora, Espejo-Serna et al. (2000) reported this species from Coahuila; this report is likely based on a misidentification. For example, Palmer 266, collected in Saltillo, Coahuila, and determined as B. arizonicus by Beetle in 1972, was found to be B. carinatus upon examination.

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Ecology: —This species is a winter-spring ephemeral and occurs in stabilized sand dunes, on slopes, along dried creek bottoms and roadsides often on volcanic soils; associated with Fouquieria columnaris ( Kellogg 1860: 101) Kellogg ex Curran (1885: 133) and Ambrosia dumosa (A. Gray in Frémont 1845: 316) Payne (1964: 422). Elevation: 10–1124 m.

Common Names: ― Arizona brome (English).

Comments: ― Bromus arizonicus is a duocecaploid, and Stebbins et al. (1944) hypothesized that it may be an intersubgeneric allopolyploid derived from B. catharticus (sect. Ceratochloa ) and the hexaploid B. berteroanus (sect. Neobromus), or an unknown close relative of the latter. It can be difficult to distinguish from B. carinatus (octoploid), from which it differs by its annual habit, upper glumes that are approximately equal in length to the lowest lemmas and lemmas usually with hairs along the margins. Also, most branches are shorter than their spikelets, resulting in erect and narrow inflorescences. This latter characteristic is not helpful for distinguishing the species in Baja California, as most individuals of B. carinatus from this region also have narrow, short-branched inflorescences. Elsewhere in México panicles of B. carinatus are more open with longer branches.

Some authors have treated B. arizonicus as a synonym of B. carinatus . Soderstrom & Beaman (1968) were not able to distinguish the taxa in Baja California, and treated all plants as B. carinatus , including two cited in the protologue of B. arizonicus: Wiggins 5291 and Epling & Stewart s.n. Several specimens at SD determined as B. carinatus var. arizonicus by F.W. Gould in 1978, but later determined as " Bromus carinatus H. & A., near B. marginatus Nees " by G.L. Stebbins in 1980 ( Gould & Moran 1981), are readily identifiable as B. arizonicus (Gentry & Cech 8875, Purer 7166A, Moran 16999, 16930, 16880, 6551). Specimens from the Sonoran desert in Arizona were recently found to be difficult to distinguish, except as ephemeral (annual) vs. perennial (R. Felger pers. comm. 2014, Felger 2014; also see comments of J.R. Reeder in Halvorson & Guertin 2003).

Specimens Examined:― MÉXICO. Baja California: 2.0 km Nof Colonia Guerrero, [30.75°N, 116°W], 80 m, 3 April 1958, P. H . Raven , H . Lewis & H . Thompson 12141 ( GH); 16 km SE of El Rosario, 30°N, 115.6167°W, 210 m, 18 April 1958, P. H . Raven , M . Mathias & J . Turner 12496 ( GH); 24.3 mi Eof Rosario, 32.3333°N, 116.62°W, 11 April 1931, I. L . Wiggins 5291 ( GH, MICH-1119175 , NY, RSA-POM-265012 , US) ; 7–8 mi Sof Punta Prieta , 28.86°N, 114.2833°W, 29 March 1973, H. S . Gentry & F . Cech 8875 ( MICH-1119163 , RSA-POM- 5688867 , SD-86524 , US-2079818 ); Arroyo Agua Amarga, southern San Pedro Mártir , 30.75°N, 115.2167°W, 823 m, 13 May 1941, I. L . Wiggins 9952 ( US-1842711 ); Isla del Norte, Los Coronados , [32.4167°N, 117.25°W], 20 March 1966, R. N . Philbrick & E. R . Blakley B66-223 ( RSA-POM-638847 ); Isla San Martín , [30.5°N, 116.1167°W], ca. 60 m, 1 April 1988, R. F . Thorne 63172 ( RSA-POM-500962 ); Rosario Wash , 10 April 1931, I. L .

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Wiggins 5241 (MICH-1119179, NY, GH, US-1721766); S Coronado Island , [32.4167°N, 117.25°W], 50 ft, 19 March 1966 , E. R. Blakley 6702 ( RSA-POM-638849 ); Santa Catarina Landing , [29.5926°N, 115.258°W], 10 March 1930 , I. L. Wiggins 4425 ( MICH-1119180 , US-1721772 ); San Quintín , 17 April 1958 , [30.5602°N, 115.9425°W], 30 m, P. H. Raven , M. Mathias & J. Turner 12346 ( GH); San Quintín , [30.5602°N, 115.9425°W], 5 April 1936 , C. Epling & Wm. Stewart s.n. ( MICH-1119270 ); Arroyo Socorro, Socorro wash, 16 mi Eof Hwy. 1, [30.3167°N, 115.8167°W], 24 April 1984 , P. M. Peterson & C. R. Annable 02273 ( CAN, US); 1 km Eof El Morro , 32.2583°N, 116.9792°W, 10 m, 27 March 1982 , R. Moran 30069 ( SD-110770 ); Santo Tomás, near Paloma Rch Trailer Park , [31.57°N, 116.52°W], 180 m, 16 September 1979 , J. R. Reeder & C. G. Reeder 7215 ( SD-116029 ); Tijuana River bottom, 32.5333°N, 117.0167°W, 20 m, 18 April 1981 , R. Moran 29552 ( SD-108517 ); Coronado Islands , N Island, on top, 32.4375°N, 117.3°W, 100 m, 20 March 1958 , R. Moran 6551 ( SD-49332 ); Sof Playa Hotel, Ensenada, 31.8667°N, 116.6167°W, 25 March 1937 , E. A. Purer 7166 A ( US-1648131 , SD-39682 ); 2 mi SE of El Progreso , 29.4667°N, 115.1667°W, 490 m, 25 March 1970 , R. Moran 16880 ( SD-76758 ); Puerto Santa Catarina , 29.5167°N, 115.2667°W, 5 m, 27 March 1970 , R. Moran 16999 ( SD-76828 ); Arroyo Santa Catarina, Ammonite area 5 mi Nof the mouth of arroyo, 29.5833°N, 115.2333°W, 75 m, 26 March 1970 , R. Moran 16930 ( SD-76816 ); Coronado Islands , N Grande Island, [32.4467°N, 117.2983°W], 25 March 1990 , T. Oberbauer 90-30 ( SD-162832 ); Coronado Islands , Eslope above landing on N island, 32.4467°N, 117.2983°W, 50 m, 3 March 1970 , R. Moran 16795 ( SD- 76240 ); Mpio. Ensenada, City of Ensenada , 31.8606°N, 116.6178°W, 31 March 2007 , F. Casillas 73 ( SD-182569 ); Ensenada, Todos Santo Bay , 31.8606°N, 116.6178°W, 21 March 1948 , H. S. Gentry 7911 ( RSA-POM-364157 ); Cuesta de Jarahuai and vicinity, 732–914 m, 31.6°N, 116.3833°W, 6 April 1950 , H. S. Gentry & F. Cech 9005 ( ARIZ-265015 , MICH-1119162 , US-2810955 , US-2079823 ); Arroyo Cataviña , in bed of arroyo near the mouth, 29.4167°N, 115.1°W, 10 m, 29 March 1970 , R. Moran 17048 ( MSC-276930 , SD-76825 ). Sonora: Mpio. Elías Calles. 16.6 km on Mex. Hwy 8 SW of Sonoyta, 31º47’30”N, 112º59’15”W, 415 m, 29 April 1991 , Felger 91-56 ( ARIZ-327325 , det. R. Felger, 2014); Imuris , 30.7833°N, 110.8583°W, 840 m, 31 May 1995 , T. R. Van Devender 95-546 ( ARIZ-319529 , det. R. Felger 2014) .

Figures

FIGURE 5. Bromus arizonicus. A. Habit. B. Inflorescence. C. Lemma D. Spikelet. Illustration by C.T. Roché, reproduced from Barkworth et al. (2007) with permission.

FIGURE 6. Bromus arizonicus. Wiggins 5241 (MICH-1119179).

FIGURE 7. Geographical distribution of Bromus arizonicus in México.