Poa pratensis irrigata (Lindm.) H. Lindb., Sched. Pl. Findland. Exs. 2: 20. 1916.

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 : 48

16d. Poa pratensis irrigata (Lindm.) H. Lindb., Sched. Pl. Findland. Exs. 2: 20. 1916. Fig. 18 A, B

Poa humilis Ehrh. ex Hoffm., Deutschland Flora 1: 45. 1800. Type: Sweden, Uppsala, Ehrhart 115 (isotypes: LE! plant B on sheet, plant A on sheet is Poa pratensis subsp. alpigena, LE! [2 sheets] plant B ex E. Fries Herb. Normal, LE-TRIN-2598.02! plant B ex E. Fries Herb. Normal).

Poa bourgeaei E. Fourn. Mexic. Pl. 2: 113 1886. Type: Mexico, Distrito Federal, pres San Angel, 23 May 1865, E. Bourgeau 225 (isotype: US-89690! fragm.).

Description.

Tufts sparse or dense to loose, sometimes forming turf, or some or all shoots solitary; dark green, or bluish-gray-green; tillers mainly extravaginal. Culms 8-30(-50) cm tall. collar margins commonly retroresly strigulose. Ligules of lower culm and tiller leaves commonly pubescent abaxially; blades of cauline leaves flag leaf blades flat, thin, soft; sterile shoot blades usually less than 15 cm long, 2-4.5 mm wide, usually glabrous adaxially. Panicles 2-10 cm long, open, broadly pyramidal; rachis with 1-3(-5) branches per node; primary branches widely spreading, smooth or sparsely to moderately scabrous; longest branches 1.5-6 cm, with 4-8 spikelets. Spikelets lanceolate to broadly lanceolate, not bulbiferous; glumes subequal, often glaucous; lower glumes (1-)3-veined; upper glumes usually subequaling the lowest lemma; lemmas 3-6(-6) mm long, finely muriculate, intermediate veins glabrous; paleas scabrous, medially glabrous over the keels, intercostal region glabrous. 2 n = 54, 56, 65, 80, 82-147.

Distribution.

The subspecies occurs in Eurasia, North America (Canada, Greenland, USA, and Mexico (Veracruz).

Ecology.

The introduced subspecies iscultivated as a turf grass in mesic, cool temperate regions.

Specimens examined.

Mexico. Veracruz: Municipio Perote, Escobillo, 19°31'30"N, 97°13'W, 3000 m, Mar 1991, H.R.Sandoval 78 (MEXU).

Discussion.

The subspecies is often cultivated for pastures and lawns and many of the cultivars originate from Eurasian selections, or plants selected from foreign strains established in North America; and cultivated strains are certainly present in Mexico (see type of Poa bourgeaei ). Of more than 700 chromosome counts RJS has compiled from the literature for this taxon the vast majority are between 2 n = 80 and 147. Cultivated forms selected for lawns with soft flat leaves and loose tufts have generally been referred to Poa pratensis subsp. irrigata, which is considered Eurasian in origin. Some authors suggest Poa pratensis subsp. latifolia (Weihe ex Mert. & W.D.J.Koch) Schübl. & G.Martens is the same taxon and is the correct name ( Portal 2005). At the species rank this subspecies has been called Poa humilis Ehrh. ex Hoffm. and Poa subcaerulea Sm. Poa pratensis is possibly the World’ s most complex species, fascinating in itself, but of which we know both much and too little.

Figures

Figure 18. Poa pratensis L. A, B Poa pratensis subsp. irrigata (Lindm.) H. Lindb. A habit B spikelet C-J subsp. pratensis C habit D sheath, ligule blade lateral view E blade apex lateral view F blade apex adaxial view G inflorescence H branch segment with spikelets I spikelet J floret. Drawings from Soreng (2007).