Poa annua L., Sp. Pl. 1: 68 1753.

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 : 10-13

2. Poa annua L., Sp. Pl. 1: 68 1753. Fig. 2 A-E

Ochlopoa annua (L.) H. Scholz, Ber. Inst. Lanschafts- Pflanzenokologie Univ. Hohenheim Beih. 16: 58. 2003. Type:Habitat in Europa ad vias. (lectotype: LINN-87.17!, right-hand plant, designated by Soreng 2000: 254).

Description.

Gynomonoecious. Annuals (rarely surviving for a second season); tufted, infrequently short stooling, tufts generally small, bases usually narrow, green to light green; tillers intravaginal (each subtended by a single 2-keeled, longitudinally split prophyll over 0.5 cm long), without cataphyllous shoots, most shoots eventually flowering. Culms 2-20(-45) cm tall, spreading to erect, sometimes geniculate, leafy, slender, terete, smooth; usually 1 nodes. Leaf sheaths terete or weakly compressed, smooth, glabrous; butt sheaths papery, smooth glabrous; flag leaf sheaths 1-6 cm long, margins fused ca. 33% the length; throats and collars smooth, glabrous; ligules 0.5-3(-5) mm long, decurrent, abaxially smooth, glabrous, apices obtuse to truncate; blades 1-10 cm long, 1-3(-6) mm wide, flat or weakly folded, thin, soft. smooth, margins usually slightly scabrous, broadly prow-tipped; blades all about equal in length, flag leaf blades well developed. Panicles 1-7(-10) cm long, 1.2-1.6 × long as wide, erect, open, pyramidal to rhomboid, moderately congested to sparse; rachis with 1-2(-3) branches per node; primary branches ascending to spreading or reflexed, straight, terete or sulcate, smooth; lateral pedicels less than 1/3 the spikelet in length, smooth; longest branches 2-4(-5) cm, spikelets crowded or loosely arranged. Spikelets 3-5 mm long, ovate, laterally compressed; not bulbiferous; florets 2-6, proximal hermaphroditic, distal often pistillate; rachilla internodes terete, smooth, glabrous, more or less concealed or exposed, distal internode less than 1/2(-3/4) length of distal lemma; glumes unequal, smooth, distinctly keeled, keels smooth; apex acuminate to acute or obtuse, sharp pointed or slightly blunt; lower glumes 1-2.2 mm long, 1-veined, narrowly lanceolate, often slightly sickle shaped, or subulate, apex acute; upper glumes 1.5-2.5 mm long, shorter than or subequaling lowest lemma,3-veined, lanceolate to oblanceolate, apex obtuse to acute; calluses glabrous; lemmas 2.2-3.3(-4) mm long, broadly lanceolate, green to light green, sometimes slightly anthocyanic, distinctly keeled, smooth throughout, keels, marginal, and usually intermediate veins moderately to densely crisply puberulent to long villous, rarely glabrous throughout, between veins glabrous, intermediate veins prominent, margins and edges smooth, apices obtuse to acute; paleas keels smooth, short to long villous, rarely glabrous over the keels. Flowers cleistogamous to chasmogamous; lodicules 0.45-0.5 mm long, broadly lanceolate to ovate, with 1 (rarely 2) short lateral lobe(s); anthers 0.6-1.1 mm long, oblong prior to dehiscence, often vestigial in distal flowers of a spikelet. Caryopses 1.6-1.8 mm long, elliptical in side-view, subcylindrical in cross-section, light brown, sulcus almost flat, hilum 0.15 mm long, oval, grain free or adherent to the palea. 2 n = 28.

Distribution.

The species is distributed Worldwide, primarily in temperate and subtropical regions. In Mexico it is recorded from all states, except Campeche, Nayarit, Quintana Roo, Sinaloa, Tabasco, and Yucatán.

Ecology.

The species is a gynomonoecious, ruderal annual (infrequently a short-lived perennial), and is found in waste ground, lawns, gardens, trails, sidewalks, roadsides, fields ranging from sea level to over 4500 m. The species can potentially flower throughout the year.

Specimens examined.

Mexico. Aguascalientes: Municipio Aguascalientes, Aguascalientes, 18 Sep 1978, J.A.Zamarripa-D. (MEXU). Baja California: Guadalupe Island, North Twin Cañon, 50 m, 24 Apr 1958, R.Moran 6622 (US). Baja California Sur: reported by Espejo Serna and Lopez Ferrari (2000). Chiapas: Escuintla, 3 Oct 1936, E.Matuda 312 (US). Chihuahua: vic. of Chihuahua, 1300 m, 27 Apr 1908, E.Palmer 28 (US). Coahuila: Saltillo, Apr 1898, E.Palmer 6 (US). Colima: reported by Espejo Serna and Lopez Ferrari (2000). Durango: Durango, Apr 1896, E.Palmer 97 (TAES, US). Distrito Federal: Azcapotzalco, 27-30 Jul 1910, A.S.Hitchcock 5929 (US). Guanajuato: Municipio Cortazar, Ejido del Rancho del la Gavia, 2330 m, 9 Oct 1996, s. collector (MEXU). Guerrero: Municipio Tlacotepec, Cerro Teotepec, 3350 m, 5 Dec 1963, J.Rzedowski 18145 (MEXU, MSC). Municipio General Heliodoro Castillo, El Jilguero, 2600 m, 30 Oct 1998, N.Diego 8146, B.Ludlow & A.Acosta (MEXU, lemmas glabrous or nearly glabrous). Hidalgo: Pachuca, 6-7 Sep 1910, A.S.Hitchcock 6747 (US). Jalisco: Mt. Nevada, 23-24 Sep 1910, A.S.Hitchcock 7154 (US). Michoacán: 8-10 mi NW of Ciudad Hidalgo, 2850-3000 m, 18 Mar 1949, R.McVaugh 9902 (US). Municipio Tallpujahua, Presa Brockman, 2760 m, I. García 3603 & Y.H.-deG (MEXU, stooling form). Morelos: Morelos, El Parque, 31 Aug 1910, C.R.Orcutt 3858 (US). Mexico: woods near El Oro, 9000 ft [2745 m], 14 Sep 1901, C.G. Pringle 9589 (TAES).Ixtaccihuatl, Oct 1905, C.A.Purpus 1618 (US). Nuevo León: Cerro Potosí, 9000 ft [2745 m], 7 Jul 1963, R.L.McGregor 267, L.J.Harms, A.J.Robinson, R.del Rosario, R.Segal (US). Oaxaca: Oaxaca, 5000 ft [1525 m], 30 May 1894, C.G.Pringle 4671 (US). Puebla: Tehuacán, 9 Aug 1910, A.S.Hitchcock 6049 (US), Ixtaccihuatl S flank, in circ E of the "portal" N of La Amacuilecatl "Los Pies", 19.1543°N; 98.6307°W, 4400 m, 2 Oct 1987, R.J.Soreng 3323 & N.Soreng (US, stooling form). Querétaro: Querétaro, 24-25 Jul 1910, A.S.Hitchcock 5829 (US). San Luis Potosí: Alvarez, 28 Sep to 3 Oct 1902, E.Palmer 173 (US). Sonora: Guadalajara, Jul-Oct 1886, E.Palmer 483 (US). Tamaulipas: Reported (Espejo Serna and Lopez Ferrari 2000). Tlaxcala: Municipio A. Arista, 5 km al sur de San. Felipe Hidalgo, 3000 m, 15 Dec 1988, R.Acosta 2689 & M. Sánchez (MEXU). Veracruz: Jalapa, 4600' [1400 m], 2-4 Sep 1910, A.S.Hitchcock 6625 (US). Zacatecas: near Plateado, 1 Sep 1897, J.N.Rose 2712 (US).

Discussion.

This Old World species is naturalized throughout temperate regions of the New World. The species was already widespread in Mexico by the mid-1800's: Popocatepetl, H.G. Galeotti 5828, 5854 (US fragm. ex CAEN in 1837-1847); Orizaba, F. Müller 2094 (US fragm. ex P in the 1850's); and San Luis Potosí, M. Virlet-d’Aoust 1372, 1394 (US fragm. ex P in 1851). Above we list a single specimen per state for this species, except when there is notable morphological variation. We cite the oldest voucher seen that came from the state. The species probably occurs sporadically in additional states and is surely in Sinaloa but without a collection. Plants from wet areas at high altitudes can perenniate by rooting at the nodes (noted in specimens cited from Michoacán and Puebla), and such forms have been called Poa annua var. reptans Hausskn. We suspect that such forms arise repeatedly in plastic response to the environmental conditions, rather than from unique genetic variation, and are not particularly useful to recognize taxonomically. A form with the lemmas and paleas glabrous or nearly glabrous occurs sporadically around the world, and has been found in Guerrero. All collections from Mexico we have seen identified as " Poa infirma " belong to Poa annua , and only one specimen was redetermined by us as Poa infirma from among hundreds of Poa annua specimens. DNA data support the hypothesis that Poa annua , a tetraploid species, arose from hybridization between two Eurasian diploid species, Poa infirma × supina Schrad. ( Soreng et al. 2010). Poa infirma is a short-lived annual and Poa supina is a stoloniferous perennial. Species of this complex [ Poa sect. Micrantherae Stapf; syn. Poa sect. Ochlopoa Asch. & Graebn., Ochlopoa (Asch. & Graebn.) H. Scholz.] have spikelets with perfect lower florets and pistillate upper florets, smooth branches and spikelet bracts, and soft puberulent lemma keels and marginal veins, soft puberulent palea keels, and glabrous calluses. Poa annua frequently approaches Poa infirma in form, presumably in part due to expression of particular genes, or segregation of those genes toward the parental species. This hypothesis explains the difficulty of identifying true diploid Poa infirma . In a separate review of US New World specimens previously identified as Poa annua or Poa infirma by Hildemar Scholz (B, dets. of 2007), only one specimen from Central America was identified as other than Poa annua (see Poa infirma discussion below).

Figures

Figure 2. A-E Poa annua L. A habit B inflorescence C glumes D floret with palea and anthers E florets F-H Poa infirma Kunth F habit G spikelet H floret with palea and anthers. Drawings from Soreng (2007).