Poa infirma Kunth, Nov. Gen. Sp. (quarto ed.) 1: 158. 1815 [1816].

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 : 32-33

10. Poa infirma Kunth, Nov. Gen. Sp. (quarto ed.) 1: 158. 1815 [1816]. Fig. 2 F-H

Megastachya infirma (Kunth) Roem. & Schult., Syst. Veg., editio decima sexta 2: 585. 1817. Eragrostis infirma (Kunth) Steud., Nomencl. Bot. (ed. 2) 1: 563. 1840. Ochlopoa infirma (Kunth) H.Scholz, Ber. Inst. Lanschafts-Pflanzenokologie Univ. Hohenheim Beih. 16: 59. 2003.Type: Nova Granada, Aug 1801, Humboldt & Bonpland 134 (holotype P-HUMB!; isotypes: B-WILLD - 1974! pl. 223, LE-TRIN-2638.01 fragm. & illustr.!, US-1851276! fragm. ex P, US-2851277! fragm. ex P-HUMB).

Description.

Gynomonoecious or hermaphroditic. Annuals; tufted, tufts mostly small, bases narrow, light green; tillers intravaginal (each subtended by a single 2-keeled, longitudinally split prophyll over 0.5 cm long), without cataphyllous shoots, most shoots flowering. Culms 2-18 cm tall, spreading to erect, sometimes geniculate, slender, leafy, terete, smooth; usually 1 node exerted. Leaf sheaths terete or weakly compressed, smooth, glabrous; butt sheaths thin papery; flag leaf sheaths 1-5 cm long, margins fused ca. 33% their length; throats and collars smooth, glabrous; ligules 0.5-3 mm long, decurrent, abaxially smooth, glabrous, apices obtuse to truncate; blades 1-7 cm long, 1-3(-4) 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 1-6 cm long, 1.5-3 × long as wide, erect, more or less open, rhomboid, moderately congested; rachis with 1-2(-5) branches per node; primary branches mostly ascending, straight, terete or sulcate, smooth; lateral pedicels less than 1/5 the spikelet in length, smooth; longest branches 1.5-3 cm, spikelets crowded along the branches, with up to 10 spikelets from the base to distal 1/2. Spikelets 3-5 mm long, lanceolate, laterally compressed; not bulbiferous; florets 2-6, proximal hermaphroditic, distal sometimes pistillate; rachilla internodes terete, smooth, glabrous, usually exposed in side view, distal internode 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 1-1.5 mm long, 1-veined, narrowly lanceolate, often slightly sickle shaped, or subulate; upper glumes 2-2.5 mm long, usually shorter than or subequaling lowest lemma, 3-veined, lanceolate to oblanceolate; calluses glabrous; lemmas 2-2.5 mm long, broadly lanceolate, light green, distinctly keeled, smooth throughout, keels, marginal, and intermediate veins densely crisply puberulent to long villous, between veins glabrous, intermediate veins prominent, margins and edges smooth, apices obtuse to acute; paleas keels smooth, short to long villous over the keels. Flowers cleistogamous to weakly chasmogamous; lodicules 0.15-0.2 mm long (the upper sometimes rudimentary); anthers 0.1-0.55 mm long, more or less spherical to short elliptical prior to dehiscence, distal flower ones sometimes vestigial. Caryopses 1.4 mm long, elliptical in side-view, subcylindrical in cross-section, pale green, sulcus almost flat, hilum 0.1 mm long, round to oval, grain slightly adherent to the palea. 2n = 14.

Distribution.

The species is indigenous to western Eurasia, Middle East (especially Mediterranean countries), and North Africa; introduced in Australia and the Americas. In North America the species is known from sporadic locations in British Columbia, Canada; California, Georgia, Oregon in the USA; and Baja California, Mexico. In South America the species is known from Argentina, Bolivia, Chile, Columbia, Peru, and in Central America it has been reported from Guatemala ( Soreng et al. 2003b).

Ecology.

This species occurs from near sea level in temperate regions with Mediterranean climates, to elevations with cool temperate to frigid climates in tropical latitudes (to 4400 m). Flowering late winter to early spring.

Specimens examined.

Mexico. Baja California: between Maneadaro and San Carlos Hot Springs, 18 Apr 1973, A.A.Beetle M-2838 (TAES).

Discussion.

This diploid species name was applied to various early collections from Mexico, and later treated as synonym of Poa annua ( Hitchcock 1913, 1935). Poa annua is a tetraploid species derived from Poa infirma × Poa supina ( Soreng et al. 2010) that sometimes looks quite similar to its parental types, making identifications challenging. Poa infirma has more crowded and small spikelets on branches that are more ascending, in addition to shorter anthers [0.2-0.5(-0.6) mm], and is a short-lived ephemeral. Soreng et al. (2003a) cited Poa infirma for Mexico, but review of the US vouchers by Hildemar Scholz (B), and subsequently again by RJS and also for MO and MEXU vouchers did not reveal any authentic material. Since then, one authentic specimen was found in a loan from TAES. It is expected to be present elsewhere in Mexico. It is well established in lower elevations of central and southern California west of the Sierra Nevada, and occurs at scattered high elevation locations from Colombia south to Argentina. One old collection from Guatemala, 1880s, H. vonTürckheim 907 (US) originally distributed as Poa infirma , was redetermined by H. Scholz (det. 2007) as Ochlopoa maroccana (Nannf.) H. Scholz (≡ Poa maroccana Nannf.). This is the only US specimen from the New World that he determined as this species, and RJS redetermined (det. 2011) it as " Poa infirma ?" Only one anther (0.3 mm long) was found on this specimen, pointing to Poa infirma , but the panicles are short and spreading, and more similar in aspect to Poa annua .

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).