Poa occidentalis (Vasey) Vasey, Contr. U.S. Natl. Herb. 1(8): 274-275. 1893.

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 : 37-38

13. Poa occidentalis (Vasey) Vasey, Contr. U.S. Natl. Herb. 1(8): 274-275. 1893. Fig. 4 F-M

Poa trivialis var. occidentalis Vasey, Descr. Cat. Grass. U.S. 85. 1885. Type: USA, New Mexico, Las Vegas, 1881, G.R. Vasey s.n. (lectotype: US-79610! designated by Vasey 1893: 275; isolectotypes: S-G-6757! fragm., S-G-6758! fragm., US-156871!, US-824855!, US-919188!).

Description.

Hermaphroditic. Perennials, short-lived; tufted, tufts fairly dense, usually medium girth and height, bases narrow or moderately wide, green, to bluish-green; tillers intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), and extravaginal (basally cataphyllous), all erect. Culms 20-110 cm tall, erect, slender to stout, leafy, slightly compressed, smooth or scabrous; nodes terete, (3-)4-6, (1-)2-4 exerted. Leaf sheaths distinctly compressed and keeled, usually densely retrorsely scabrous, rarely lightly scabrous, margins not ciliate; butt sheaths papery in age, smooth, glabrous; flag leaf sheaths 5-22 cm long, margins fused (20-)15-50(-60)% the length, subequal to its blade; ligules 3-12 mm long, abaxially densely scabrous, apices acute to acuminate; blades (1.2-)1.5-6(-10) mm wide, flat, lax, abaxial and abaxial surfaces and margins scabrous along the veins, broadly prow-tipped; flag leaf blades 4-18(-30) cm long. Panicles (6-)12-40 cm long, nodding, lax, eventually open, pyramidal, moderately congested, spikelets numerous, to 200+; rachis with (2-)3-7 branches per node; primary branches eventually spreading, drooping, angled, angles densely scabrous; lateral pedicels mostly 1/4-1/2 the spikelet in length, sca brous; longest branches (3-)5-18(-23) cm, with (5-)8-40(-120) spikelets. Spikelets (3-)4-7(-8) mm long, ovate, laterally compressed; not bulbiferous; florets 3-7, hermaphroditic; rachilla internodes terete, less than 1 mm long, smooth or slightly muriculate, glabrous; glumes distinctly keeled, keels scabrous, apex acuminate; lower glumes 2-3.5 mm long, 1-3-veined; upper glumes 2.5-4.2 mm long, shorter than or subequaling lowest lemma, 3-veined; calluses dorsally webbed, web distinct, hairs woolly; lemmas 2.6-4.2 mm long, narrowly lanceolate, distinctly keeled, scabrous distally, keels to 1/2 and marginal veins to 1/3 short to long villous, intermediate veins and between veins usually sparsely softly puberulent, intermediate veins prominent, apices narrowly acute; paleas scabrous, glabrous over the keels. Flowers mainly cleistogamous; lodicules 0.6 mm long, lanceolate; anthers 0.3-1.0 mm long. Caryopses 2 mm long, elliptical-fusiform in side-view, strongly laterally compressed, light brown, sulcus narrow, shallow, hilum 0.2 mm long, elliptical, grain adherent to the palea. 2 n = 14, 28.

Distribution.

The species is known from Arizona, Colorado, New Mexico, and Texas, USA; and Coahuila, Mexico (Madera del Carmen).

Ecology.

The species occurs on slopes in wooded canyons with Pinus , Pseudotsuga , Cupressus , Abies , Ceanothus , Cornus stolonifera Michx., Bromus richardsonii Link, Festuca viridula Vasey, Festuca thurberi Vasey, and Quercus ;ranging between 2280-2550 m. Flowering August to September.

Conservation status.

The species is rare in Mexico.

Specimens examined.

Mexico. Coahuila: Madera del Carmen; canyon above Campo El Dos, 28°59'23.6"N, 102°36'43.0"W, 2280-2320 m, 8 Sep 2005, P.M.Peterson 18918 & J.Valdes-Reyna (US; DNA voucher, unpublished). 13.8 mi NE of Los Pilares, 28°57'13.0"N, 102°35'7.3"W, 2335 m, 21 Sep 2007, P.M.Peterson 20979, J.M.Saarela, S.Lara-Contreras & J.Reyna-Alvarez (US). 1.8 mi from Campo Uno, up the road towards the summit, 29°0'14.2"N, 102°36'22.7"W, 2547 m, 23 Sep 2007, P.M.Peterson 21036 J.M.Saarela, S.Lara-Contreras & J.Reyna-Alvarez (US).

Discussion.

This is the first report Poa occidentalis for Mexico, and is a range extension of 460 km to the southeast. This species was previously known to occur from eastern Arizona (White Mountains) to southern Colorado, south through the mountains of New Mexico to the Guadalupe Mountains of Eddy County, Texas ( Soreng 1985, 2007). Three new collections were gathered in northern Mexico in 2005 and 2007, in the upper coniferous forest belt of the Madera del Carmen, and these presumably represent a relictual population. The first glume of Poa occidentalis was reported as 1-veined (Soreng ibid.), whereas it is principally 3-veined in the Mexican specimens, but re-examination of New Mexican specimens revealed this character state to vary from 1 to 3 veins. Poa occidentalis can be distinguished from other species Poa in Mexico by the following characters: its tall stature; short-lived perennial nature; long acute to acuminate, abaxially scabrous ligules that are longer than the leaf blades are wide; long and widely open, many spikeleted panicles; and anthers 0.5-1.0 mm long. Vasey (1893) considered his Poa trivialis var. occidentalis published in 1885 to be "without description", and taxonomists have traditionally accepted this. However, in 1885, he provided an adequate diagnosis of his indi genous Poa occidentalis var. occidentalis, from Colorado and New Mexico, by comparing it to the introduced Poa trivialis L., which he described and noted had been established in the United States outside of cultivation (mainly in the eastern USA at low to moderate elevations). The isolectotypes indicate "July 1881", and "Mts. near Las Vegas", or "Mts. west of Las Vegas", but there is no habitat "at Las Vegas" for the species, we presume all the material was collected in the mountains near or west of Las Vegas and to be of the same gathering as the lectotype. Vasey’s collection notebooks at US are not helpful and there is only one listing (no. 566) as Poa trivialis under Arizona and New Mexico 1881 (without other details).

Figures

Figure 4. A-E Poa bigelovii Vasey & Scribn. A habit B blade apex abaxial view C inflorescence D spikelet E lemma and palea F-M Poa occidentalis (Vasey) Vasey F habit G sheath, collar, blade, abaxial view H sheath, ligule, blade I inflorescence J branch segment with spikelets K spikelet L floret M palea. Drawings from Soreng (2007).