Poa chamaeclinos Pilg., Bot. Jahrb. Syst. 37: 379. 1906.

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 : 20-22

6. Poa chamaeclinos Pilg., Bot. Jahrb. Syst. 37: 379. 1906. Figs 6 F-I 7

Type:

Peru, in andibus elevatis supra Lima ad 4500 m, Mar 1904, A. Weberbauer 5118 (lectotype: USM!, designated by Anton and Negritto 1997: 237; isolectotypes: BAA-2510!, US-89685! fragm. ex B).

Description.

Pistillate. Perennials; mat forming, mats dense (to 20 cm across), low (mostly 1.5-3 cm tall), green; tillers intravaginal (each subtended by a single elongated, tubular prophyll), without cataphyllous shoots. Culms 1-3.5(-5) cm tall, erect or arching, leafy, terete or weakly compressed, smooth; nodes 0-1, not exerted, deeply buried in basal tuft. Leaves mostly basal; leaf sheaths laterally slightly compressed, indistinctly keeled, basal ones with cross-veins, smooth or with sparse hooks, glabrous; butt sheaths becoming papery to somewhat fibrous, smooth, glabrous; flag leaf sheaths 0.8-2 cm long, margins fused ca. 50-60% their length, 2-3 × longer than its blade; throats and collars smooth or slightly scabrous, glabrous; ligules 0.5-3.2 mm long, decurrent, scarious, milky-white, abaxially smooth or scaberulous, upper margin entire or denticulate, apices obtuse to acute, sterile shoot ligules equaling or shorter than those of the upper culm leaves; blades 1-2.2 cm long, 1-1.5 mm wide (expanded), folded, often with involute margins, slightly thick, soft, abaxially smooth, veins slightly expressed, margins proximally scabrous, distally smooth, adaxially smooth or lightly scaberulous, with two rows of buliform cells, but otherwise level, apices abruptly prow-tipped; flag leaf blades like the others; sterile shoot blades like those of the culm. Panicles 0.8-1.5 cm long, 3-7 mm wide, erect, densely contracted, narrowly elliptic to ovoid, erect, slightly secund, included in the leaves or eventually exerted by up to 3(-4) cm, congested, with 5-20 spikelets, peduncle smooth; rachis with 1-2 branches per node; primary branches erect, appressed, stiff, slightly angled, smooth or distally slightly to moderately scaberulous on the angles; lateral pedicels less than 1/4 their spikelet in length, scabrous angled, hooks moderate in size to sub-ciliate; longest branches 0.3-0.4 cm, with up to 4 spikelets, flowered from near the base. Spikelets 4-4.5 mm long, 1.5-2.5 mm wide; 2-3 × as long as wide, ovate, laterally compressed, not bulbiferous, slightly lustrous, two toned; florets (1-)2, pistillate; rachilla internodes terete, mostly 0.2-0.5 mm long, smooth, glabrous; glumes obovate to sub-flabellate, herbaceous and pale green below, scarious bronzy and sometimes anthocyanic in margins and apex, veins distinct, equal to subequal, distinctly keeled, sometimes a bit asymmetrical, smooth, margins broadly scarious-hyaline, edges entire or dentate, smooth, apices dentate to shortly lacerate; lower glumes 2.9-3.3 mm long, 3-veined; upper glumes 3.2-3.3 mm long, 3-veined; calluses glabrous; lemmas 3.5-4.2(-4.5) mm long, 5-veined, obovate to sub-flabellate, thinly herbaceous and pale green below, strongly keeled, surfaces smooth, glabrous intermediate veins distinct, upper margins broadly bronzy-anthocyanic, apices obtuse, sometimes lacerated or dentate; paleas glabrous, keels smooth, closely spaced, between keels smooth (or with a few hooks), Flow ers; lodicules 0.4-0.5 mm long, broadly lanceolate, apex rounded; anthers vestigial, 0.1-0.2 mm long. Caryopses 1.8 mm long, elliptical in side-view, cylindrical in cross-section, sulcus indistinct, hilum 0.4 mm long, oval, grain free from the palea, stigma densely plumose. 2 n = unknown.

Distribution.

The species occurs in Bolivia, Peru, and Mexico. In Mexico it is restricted to Volcán Ixtaccihuatl, and possibly to the state of Puebla.

Ecology.

The species occurs as isolated mats in wet meadows and on gentle slopes between 4300-4450 m. The spikelets of this species are strictly pistillate and seed is produced apomicticly. Flowering September to October.

Specimens examined.

Mexico. Mexico or Puebla: Ixtaccihuatl, Jan 1909, C.A.Purpus 3772 (US-924996). Puebla: Ixtaccihuatl, south side of mountain, ca. ½ km NE of summit of Pies, 4300-4350 m, 16 Sep 1958, J.H.Beaman 2555 (MEXU-58016, MSC, US-2381604, TEX, WIS); ditto, in the circ E of the "portal" N of La Amacuilecatl (Los Pies), 19.1507°N; 98.6294°W, 4400-4450 m, 3 Oct 1987, R.J.Soreng 3315 & N.Soreng (US, Soreng 1990, cpDNA voucher).

Discussion.

In Mexico, the Purpus 3772 collection long passed under the name Poa villaroelii Phil. ( Hitchcock 1913, Espejo Serna et al. 2000, Dávila Aranda et al. 2006). However, the first author has studied Poa villaroelii in Chile and the herbarium (including types), and concludes the Mexican specimens are not applicable ( Soreng et al. 2003, Soreng and Peterson 2007). Poa chamaeclinos has strictly pistillate spikelets, reproduces apomicticly, and has broad, bronze-colored, scareous-hyaline lemma apices, whereas Poa villaroelii (now treated as Poa acinaciphylla E. Desv.) has perfect flowers (anthers 2.2-2.8 mm long) with narrow, whitish, scareous-hyaline apices, and is a much more robust species. Clayton et al. (2006 onwards; accessed Dec. 2011) mistakenly accepted Poa acinaciphylla in Mexico and South America and Poa chamaeclinos only in South America.

A further taxonomic problem arises when trying to reliably distinguish Poa chamaeclinos from Poa perligulata Pilg., a closely related species of South America that also has pistillate spikelets and reproduces apomicticly. Negritto and Anton (2000) argued that Poa chamaeclinos differs by lacking rhizomes, and by having short ligules [0.3-1 (-3) mm long] that have truncate apices with entire, erose or denticulate margins versus longer ligules [1.5-3 (-6) mm long] with acute apices and entire margins in Poa perligulata . The Mexican plants lack rhizomes and the vegetative branching seems to be entirely intravaginal (in Poa perligulata some vegetative extravaginal branching is always present). The ligules in the Mexican specimens are ca. 3 mm long, albeit with the denticulate margins. The ligule length overlaps between these taxa and the margin character is not considered reliable for separating the species. Soreng (1990) initially accepted the Mexican plants as Poa chamaeclinos . However, Soreng et al. (2003a) decided to treat the Mexican plants as Poa perligulata since the Poa chamaeclinos isolectotype at US seemed to be a plant of drier habitat with shorter ligules, stiffer leaves, and slightly scabrous lemmas that are slightly firmer and scareous near the apex. The lectotype of Poa chamaeclinos at USM, illustrated by Anton and Negritto (1997, Fig. 5 ) seems to fit the Mexican material, whereas their lectotype for Poa perligulata does not ( Negritto and Anton 2000). They also indicate that the distinction between the two taxa is difficult and needs further wor k ( Negritto and Anton 2000). If the lack of rhizomes is a good diagnostic character for Poa chamaeclinos , then the Mexican material should be referred to that taxon. Beaman (accompanying notes with the US specimens) considered naming the Mexican plants as a new species with the epithet "cordylina". Unlike Poa gymnantha , which does not tolerate poorly drained soils, Poa chamaeclinos and Poa perligulata grow in perennially wet or "waterlogged" habitats, often with densely-interwoven vegetation. On Ixtaccihuatl, RJS recalls a large population to have occurred over much of the wet floor of the southeastern glacial circ, forming discrete, low mats to about 20 cm in diameter.

Figures

Figure 5. Poa calycina var. mathewsii (Ball) Refulio. Photo of Purpus 1633.

Figure 6. A-E Poa gymnantha Pilg. A spikelet B lemma and palea C palea D staminode and lodicules (pistillate-flower) E pistil (pistillate-flower) F-I Poa chamaeclinos Pilg. F spikelet G floret H palea I pistil (pistillate-flower) J Poa palmeri Soreng & P. M. Peterson J spikelet K-M Poa strictiramea Hitchc. K spikelet L floret M palea N-P Poa calycina var. mathewsii (Ball) Refulio N spikelet O floret P palea. A-E drawn from Peterson 12863 et al. from Peru F-I drawn from Soreng 3315 & Soreng; J drawn from Peterson 18790 & Valdes-Reyna K-M drawn from Soreng 3204 & Spellenberg N-P drawn from Beaman 1732.

Figure 7. Poa chamaeclinos Pilg. Photo of Purpus 3772.