Poa bajaensis Soreng, Madrono 48(2): 123, f. 1. 2001 [2002].

Soreng, Robert J. & Peterson, Paul M., 2012, Revision of Poa L. (Poaceae, Pooideae, Poeae, Poinae) in Mexico: new records, re-evaluation of P. ruprechtii, and two new species, P. palmeri and P. wendtii, PhytoKeys 15, pp. 1-104 : 13-15

3. Poa bajaensis Soreng, Madrono 48(2): 123, f. 1. 2001 [2002]. Fig. 3 A, B

Type:

Mexico, Baja California, Sierra San Pedro Mártir, E rim above Yerba Buena, 31°01'N, 115°W, 2700 m, 1 Jun 1968, R. Moran 15070 (holotype: US-259736!; isotypes: SD-69304!, TAES-16825!).

Description.

Hermaphroditic. Perennials; tufted, tufts dense, fairly narrow to medium girth and low to medium height (5-12 [-15] cm tall), pale green to bluish green; tillers intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), without cataphyllous shoots, sterile shoots more numerous than flowering shoots. Culms 20-50 cm tall, erect, blades strongly reduced upward, terete, smooth; nodes 2-3, smooth, upper (0-)1-2 exerted, uppermost at mid-culm. Leaves mostly basal; leaf sheaths slightly keeled, very sparsely to moderately (rarely densely, evenly, finely scabrous; butt sheaths persisting, grayish-brown, papery, their blades disarticulating, the bases smooth, glabrous; flag leaf sheaths 8-15 cm long, margins fused 29-36% their length, (2.5-)10-16 × longer than its blade; collars vestiture like that of the sheath; ligules 0.25-0.5 mm long on basal leaves, to 0.5-1.5(-2) mm long on upper culm leaves, abaxial surface and upper margins densely scabrous, apices truncate to obtuse; blades to 10(-15) cm long, 1.5-2.75 mm wide, folded or flat, margins inrolling, moderately thick abaxially smooth or lightly scaberulous (denser apically), margins scabrous, adaxially smooth or moderately to densely scaberulous, narrowly and abruptly prow-tipped; culm blades sharply reduced upward, flag leaf blades 0.1-1.5(-4) cm long. Panicles 4-13 cm long, erect, open, pyramidal, well exerted, sparse, with 16-50 spikelets, peduncles smooth, proximal internode 1.8-3.9(-5.2) cm long, smooth; rachis with branches 2-3(-5) per node; primary branches widely spreading to reflexed, fairly strict, terete to weakly angled, smooth or sparsely scaberulous proximally, smooth or moderately (rarely densely) distally, hooks not confined to rows on angles; lateral pedicels mostly about half the spikelet length, smooth or sparsely scabrous, prickles fine; longest branches 3-7 cm, with 3-15 spikelets in the distal 1/2. Spikelets 3.75-8 mm long, lanceolate, laterally compressed not bulbiferous, pale green to strongly anthocyanic; florets (1-)2-4(-6), hermaphroditic; rachilla internodes terete, 1.25-2 mm long, smooth, glabrous; glumes, lanceolate to narrowly lanceolate unequal to subequal, shorter than the first lemma, distinctly keeled, thin, smooth or lightly scabrous distally, lateral veins and apical surfaces smooth or lightly scabrous, sharply acute; lower glumes 2.5-3 mm long, ca. 1/2 the adjacent lemma in length, 1(-3)-veined; upper glumes 2.8-3.5 mm long, 3-veined, often 2 × wider than the lower one, ca. 3/4 the adjacent lemma in length, with a broad scarious-hyaline margin; calluses glabrous or webbed, web sparse, hairs to 2 mm long, woolly; lemmas 3.2-4.2 mm long, lanceolate, 5 veined, green to strongly anthocyanic, distinctly keeled, (rarely glabrous throughout), keels to 4/5 and marginal veins to 1/2 sparsely to densely sericate, between veins glabrous or sparsely puberulent in lower 1/2, smooth except for hooks on the upper keel, intermediate veins faint, margins scarious hyaline, edges smooth or with a few fine hooks, apex acute; paleas finely and closely scabrous, glabrous or in some plants medially sparsely softly puberulent, intercostal area glabrous or sparsely puberulent. Flowers chasmogamous; lodicules 1 mm long, lanceolate, apex obtuse, unlobed; anthers 1.7-3.2 mm long (rarely sterile, but then 1.7-1.8 mm long). Caryopses 1.9-2.3 mm long, elliptical in side-view, compressed, light honey-brown, sulcus narrow, shallow, hilum 0.25 mm long, oval, grain free from the palea. 2 n = unknown.

Distribution.

The species is known only from Baja California and is endemic to Sierra San Pedro Mártir.

Ecology.

This species occurs on mountain slopes, flats, and drainages, and is associated with Salix and Populus tremuloides Michx. thickets, Quercus - Pinus jeffreyi forests, and Quercus - Pinus jeffreyi - Poa lambertiana - Abies concolor forests, and open meadows in Pinus jeffreyi Balf. forests. It is found in sandy to rocky to clay, granitic, often duff-covered soils, between 1450-2950 m. Flowering May to June.

Conservation status.

The species is a narrow endemic and locally frequent.

Specimens examined.

Mexico. Baja California: Sierra San Pedro Mártir crest of range N of observatory, head of Cañada el Copal and S slope of Cerro Venado Blanco, 2500-2700 m, 3 Jun 1988, S.Boyd 2311, T.Ross, K.McCulloh (RSA). La Concepcíon, 31°01'N, 115°37'W, ca. 1450 m, 31 May 1968, R. Moran 15006 (SD, TAES). open W slope of Cerro 2828, ca. 31°02'N, 115°27'W, ca. 2800 m, 31 May 1968, R. Moran 15060 (BH, SD, TAES). 2 mi W of Vallecitos, 31°00'N, 115°29'W, ca. 2250 m, 2 Jun 1968, R. Moran 15083 (SD, TAES). 3 km NE of El Alto de Corona, 31°00'N, 115°41'W, ca. 2400 m, 20 Aug 1977, R. Moran 24555 (SD). W slope below summit of El Picacho, 30°59'30"N, 115°22'30"W, ca. 2950 m, 5 May 1978, R. Moran 25611 (SD, TAES). end of road into high end of northern sierra, ca. 64 mi. from end of paved road to Ensenada, 7200 ft [2210 m], 6 Jun 1962, J.D.Olmsted 4561 (RSA; somewhat intermediate to Poa secunda ). central [region], ca. 3 mi ESE of Prado del Corona, ca. 1 mi up canyon from southernmost aspen colony, tributary of Rio San Rafael, 8100 ft [2490 m], 9 Jun 1962, J.D.Olmsted 4711 (RSA). S of Vallecitos near Cerro la Botella Azul, 30°57'20"N; 115°25'26"W, ca. 2440 m, 27 Jun 1998, J.Rebman 5384 & A. Russell (US). near crest of mo untain range, approx. 2 mi SE of the Observatory, 31°14'N, 115°64'W, ca. 2985 m, 28 Jun 1998, J.Rebman 5384 & A.Russell (SD); "Corral Meadow", 7.5 km NW (340°) of the Observatory, 31°06'45"N, 115°29'50"W, 16 Jun 1988, A.C.Sanders 7895, R.Minnich, E.Franco, M.Salazar (RSA, SD, TAES). Vallecitos, ca. 31°02'N, 115°28'W, ca. 2430 m, 18 Jun 1985, R.F.Thorne 60858, R.Dahlgren, S.Boyd & D.Charlton (MEXU, RSA,SD); ditto, ca. 31°02'N, 115°27.5'W, ca. 2430 m, 1 Sep 1985, R.F.Thorne 61394, M.Z.Thorne, L.Thorne & T.Petrella (RSA). just above Observatory living quarters, ca. 31°02'N, 115°28'W, ca. 2600 m, 7 May 1986, R.F.Thorne 61967, T.S.Elias & P.Rojas (MO-3333160, RSA); near gate to UNAM Observatory, 31°02'N, 115°29'30"W, 2520 m, 29 May 1982, G.Yatskievych 82-190, S.Forbes, M.Gallagher, J.Evans & A.Kelley (SD). 55 mi SE of highway 1 on road towards Villecentos at Arroyo Los Alamillos, 31°0.67'N, 115°32.28'W, 2270 m, 24 Sep 2000, P.M.Peterson 15189 & J.Cayouette (US, not flowering). 62 mi SE of highway 1 towards on road towards Villecentos, 31°1.99'N, 115°20.35'W, 2490 m, 24 Sep 2000, P.M.Peterson 15197 & J.Cayouette (US, not flowering).

Discussion.

The species is endemic to the upper elevations of the Sierra San Pedro Mártir, Baja California but apparently was not collected until 1962. Reported and described as Poa orcuttiana Vasey (= Poa secunda ) by Gould and Moran (1981); the five collections they mentioned are all Poa bajaensis . Specimens were sometimes labeled as " Poa interior Rydb." (e.g., at SD and TAES). It is well marked by its sparse open panicles, short flag leaf blades, and dense fascicles of old persisting sheaths from which the blades tend to disarticulate.

Figures

Figure 3. A, B Poa bajaensis Soreng A habit B spikelet C, D Poa thomasii Refulio C habit D spikelet. A, B from Soreng (2002), drawn from holotype collection (Moran 15070) C, D from Refulio-Rodriguez (2007) as Dissanthelium californicum, originally drawn from Trask 324 in Hitchcock (1935).