Updated checklist of Poa in the Iberian Peninsula and Balearic Islands

Abstract Based on our study of 4,845 herbarium sheets of the genus Poa from the area covered by Flora iberica, namely, the Iberian Peninsula and the Balearic Islands, we recognise 24 taxa (17 species, 1 subspecies and 8 varieties), mostly perennials. Most of these taxa have wide global and/or European distributions, while two (P. legionensis and P. minor subsp. nevadensis) are Spanish endemics and two have restricted distributions (P. ligulata, Iberia–North Africa; P. flaccidula, Iberia–North Africa and the Balearic Islands, extending to Provence, France). We have studied the original publications of more than 225 names considered as synonyms, with those more historically cited in Flora iberica taken into account in this paper; a total of 26 are new synonyms. The following names are typified: P. alpina var. involucrata Lange, P. annua var. lanuginosa Sennen, P. minor subsp. nevadensis Nannf., P. paui Font Quer, P. sulcata Lag. and P. trivialis var. flaccida Willk. ex J.J. Rodr. We include P. compressa L. in the flora of Portugal for the first time and present detailed illustrations of three very interesting taxa (P. legionensis, P. minor subsp. nevadensis and P. ligulata). In addition to a general species key, we provide the following information for each taxon: synonyms, types, typification, the most relevant iconography, regional flowering time, regional and general distribution and, as supplementary material, the number of sheets examined and a list of selected materials.


Introduction
The genus Poa L., included within subfamily Pooideae, supertribe Poodae and subtribe Poinae (Soreng et al. 2015), is considered to be monophyletic. This monophyly is supported by analyses of plastid and nuclear DNA markers (Gillespie et al. 2008). In addition, evidence for reticulation between this genus and other genera in Poinae has been uncovered; the same is true within the genus itself (e.g. P. annua) (Soreng et al. 2010). The genus comprises approximately 550 annual and perennial species  of cosmopolitan distribution, primarily in cold and temperate regions. Most species are polyploids, but 9% are diploids, with an additional 4%-6%, mostly in Europe and rarely in Asia, having both diploid and polyploid populations (Soreng et al. 2010, Giussani et al. 2016. Many species are important weeds (e.g. P. annua), while others are cultivated for forage (e.g. P. pratensis) or used in pastures (e.g. P. trivialis, P. alpina and P. bulbosa) or lawns and golf courses (e.g. P. nemoralis and P. pratensis) (Watson and Dallwitz 1992).
The genus is characterised by a great diversity of sexual systems and its species can be strictly hermaphroditic, the most common reproductive system, or diclinous (Giussani et al. 2016). Apomictic reproduction by seeds, either facultative or obligate, is common in some species (reviewed in Soreng and Peterson 2012). The production of pseudoviviparous/bulbiferous spikelets occurs in some species, such as P. bulbosa and, to a lesser extent, P. alpina.
The first taxonomic treatment of Poa on the Iberian Peninsula, by Willkomm (1870), was remarkable: he recognised 15 species and numerous varieties in the territory of Spain and later increased this total by two (Willkomm 1893). In the 20 th century, 19 of the 53 species and subspecies recognised by Edmonson (1980) in Europe were included in Flora iberica, a publication also encompassing the Balearic Islands. Of these, slightly less than half were listed for Portugal (see also Franco and Rocha 1998). The latest revision to Poa on the peninsula was carried out by Hernández Cardona (1978), who basically followed Edmonson. In this revision, Hernández Cardona also defined a new section (Flaccidula Á.M. Hern.) to accommodate P. flaccidula and recognised 19 species and subspecies plus two varieties.
In a recently completed revision of the genus Poa for a future volume (XIX) of Flora iberica, we recognised 18 species and subspecies and 8 varieties. The main aim of the present paper was to present an updated checklist of the genus. The information provided includes a general key to accepted taxa as well as a list of their most important synonyms, many of which are unknown outside of the Iberian Peninsula because they are found only on herbarium sheets or published in works of limited distribution. Some of the synonyms and an accepted name are typified and updated information on the ecology and flowering characteristics of each taxon in the covered territory is given along with its regional and worldwide distribution.

Methods
The taxonomic classification scheme followed in this paper, which begins with the type species P. pratensis, reflects currently understood relationships amongst recognised sections in the genus. An infrageneric classification of accepted species of Poa in the Iberian flora is also presented in the Results section.
We reviewed 4,845 sheets housed in the following herbaria: BC, BC-Sennen, C-Lange, COI, COI-Willk., G-Boiss., GDA-GDAC, HGM, HSS, JACA, MA, MAF, MGC, SALA-SALAF, SEV, UPP-Nannf. and UNEX (acronyms according to Thiers, continuously updated). We studied the most important synonyms of each accepted name and consulted the original publications, with a special focus on names directly related to the territory covered by Flora iberica. For each accepted taxon, we recorded synonyms, types (type protologue) and, in some cases, the typification. After studying the herbarium sheets, we obtained updated information on flowering phenology and the ecology of the area. We also researched the worldwide distribution of each taxon and its presence or absence in each province covered by Flora iberica, including the territories of Andorra (And.), Portugal (Port.) and continental Spain (Spa.) plus the Balearic Islands. In the taxonomic treatment that follows, those provinces are ordered alphabetically using the same abbreviations given in Flora iberica (http://www.floraiberica.es/; see Fig. 1). If the name of a province appears in parentheses, a bibliographic citation exists but no herbarium sheet was studied to confirm it, while a question mark indicates that the bibliographic citation is not entirely reliable. A selected list of herbarium sheets studied from each province is provided in the Suppl. material 1. Finally, some observations are included as explanatory notes for most species and subspecies. The sequence of species in this checklist is not alphabetical, but instead starts with sect. Poa because that section includes the type species; species are then ordered according to phylogenetic relationships, an arrangement more or less the inverse of that adopted by other authors, i.e. from more derived clades to those in a more basal position (see Gillespie et al. 2008;Soreng et al. 2010 Ecology. Grasslands at edges of watercourses, ravines, ponds and alpine wetlands ("borreguiles"), walls, wet soils on slopes, ditches, cultivated fields, clearings surrounded by pines, holm oaks, Portuguese oaks and other oaks; edaphically indifferent; 0−2400 m a.s.l. Notes. Poa pratensis is one of the most polymorphic taxa in the genus for a variety of reasons: its great morphological and cytological variation, the predominance of agamospermy, its vegetative propagation and wide distribution, the latter due in part to its introduction into many parts of the world for use on lawns, as fodder or for soil stabilisation (Soreng and Barrie 1999). At least 220 crop varieties are recognised (Stoneberg Holt et al. 2004).

Poa legionensis
Distribution. Endemic to the CN of the Iberian Peninsula. Spa.: Av Cc Le Lu O Or (S) Sa (Za). For a representative list of studied materials, see Suppl. material 1.  Type. "Secus torrentes sabulosos exsiccatos in monte Cenisio". (Type material conserved in TO according to Kerguélen 1975, pg. 238).
Distribution. Mountainous areas of C and S Europe. Mountains of N Spain (Pyrenees, Cantabrian Mountains and N Iberian System). And. Spa.: Ge Hu L Le Lo (O) P (S) So Z. For a representative list of studied materials, see Suppl. material 1.  Notes. Poa nemoralis is a polymorphic species with two recognised patterns of variation and numerous transitional forms in the territory encompassed by Flora iberica. The first recognised variety, Poa nemoralis var. nemoralis [Poa cinerea Vill., Hist. Pl.   Flowering. May to September (October). Ecology. Meadows and grasslands, forests, gravelly areas, margins of roads and slopes; edaphically indifferent, although preferring basic substrates; (75) 540−1990 (2300) m a.s.l.

Poa chaixii
Distribution. Circumboreal (most of Europe, to SW Asia); introduced in N, C and S America (Peru, Argentina) and Australia. CN and E Spain, rarer in the south.

And. Port.: TM. Spa.: A (Ab) B (Bi) Bu (Cs) Cu Ge Gr Gu H Hu J L (Le) Lo (Lu) M Na (Or) P S Sa Sg So T Te (V) Va Vi (Z) Za. For a representative list of studied materials, see Suppl. material 1.
Notes. Plants of this species usually have a glaucous green colour. The lower (and sometimes higher) leaves of many studied herbarium specimens are missing their blades and are frequently fragmented with the ligule exposed. Inflorescences of P. compressa are frequently narrow and interrupted, with almost adpressed branches and spikelets are variable in size and number of flowers. The spikelets may be long, almost always entirely glabrous and glaucous, with 4-9 flowers or short and bear 2-5 flowers, and this variability may be present in the same population or even on the same plant. Poa compressa has not been previously listed in the flora of Portugal. Flowering. July to September. Ecology. Rocky places, stony places and high mountain waterfalls, on shale, schist and granite; (1900) 2300−3150 m a.s.l.

Poa laxa
Distribution. C and N of Europe, reaching the Carpathians, Balkans, Apennines and Pyrenees, and N America. N and NE Iberian Peninsula. And. Spa.: Ge Hu L (P). For a representative list of studied materials, see Suppl. material 1. Two subspecies of P. minor are recognised in the territory encompassed by Flora iberica. A key to their identification is given below:

Poa minor
1 Blades of most leaves conduplicate, rarely flat, those of basal and shoot leaves 0.4-1.6(-2.1) mm wide; branches of the inflorescence flexuous; spikelets ovateoblong; lemma hairy at the nerves and the base, hairs of the latter usually longer than the width of the lemma; anthers 0. inval., syn. nov. Ill. Fig. 3.   Notes. Poa trivialis is variable with regard to habit, leaf size and inflorescence morphology. The most distinctive feature of this species is the elongated ligule, which is always longer than the width of the leaf blade, ovate or ± triangular in the basal leaves and irregularly dentate or bilobed with an acute apex in the uppermost ones. In addition, the spikelets have 2 or 3 flowers and the sharp, arched glumes converge around the lemma. The base of the lemma is very woolly or extremely rarely glabrous and the hairs are clearly longer than its width.
Some plants have somewhat thickened and constricted stolons, with a more or less moniliform appearance. These individuals were described as Poa sylvicola Guss. (= P. attica var. gaditana Pérez Lara ex Willk.; = P. trivialis var. umbrosa Balansa). According to Soreng (pers. comm.), P. trivialis subsp. sylvicola (Guss.) H. Lindb. fil. is common in the Mediterranean region, while subsp. trivialis is rather infrequent and, conversely, subsp. sylvicola is infrequent northwards. Other characteristics of subsp. sylvicola are smoother sheaths and the consistent presence of hairs on the lower part of the marginal lemma veins vs. their absence in subsp. trivialis. Practically speaking, the marginal vein is hairy in Mediterranean populations but glabrous or nearly so in northern ones. In both types of populations, however, the differing combinations of forms of these characters makes it almost impossible to delimit these two taxa. Consequently, we have opted not to recognise them as separate subspecies.
Poa feratiana Boiss. & Reut. is also included here as a synonym of P. trivialis. Plants labelled as P. feratiana on herbarium sheets had 2 flowers per spikelet, which is diagnostic for this species, but this characteristic is also very common on most studied sheets of P. trivialis. In addition-as indicated by Hernández Cardona (1976) after studying the type material (G-herbarium Boissier)-some of the characteristics attributed to this species in the original description were incorrect. For instance, the number of veins of the lemma is actually 5, not 3, a feature likely overlooked by the original authors because the marginal veins are usually very close to the edge. As another example, the lemma is indeed woolly at the base, as is common in P. trivialis.
Plants with some of their spikelets completely sterile and reduced to a set of whitish or hyaline membranes are also known.
Flowering. April to July. Ecology. Stony places, cliffs, scrub clearings and understoreys, on limestone; (200)  Notes. Spikelets in this species usually have 2-3 flowers, but can have 3-7, a rare phenomenon observed more frequently in populations in NE Spain. The most distinctive characteristic of Poa flaccidula is the sericeous or appressed-hairy indumentum of the intervein zone of both the lemma and palea. This species is sometimes confused with P. annua, but, along with other differences, the latter is an annual, not a perennial. Poa flaccidula can also be confused with P. trivialis, which, like P. flaccidula, has a ligule that is longer than the width of the leaf blade and possesses hairs at the base of the lemma that are longer than its width; however, both the palea and the internerval surface of the lemma is glabrous in P. trivialis. P. flaccidula subsp. guadianensis F.M. Vázquez, Folia Bot. Extremad. 9: 66 (2016) has recently been described from Extremadura (SW Spain), but examination of the type material (HSS 65616; COF 62937 isotypus) reveals that this taxon is in no way attributable to P. flaccidula. The most we can say, given the immaturity of the specimens, is that it may be of hybrid origin, with P. bulbosa possibly one of the parents.  Sennen, Pl. Espagne n. 605. 1908, nom. nud., in sched. (MA 11165), p.p., syn. nov. Poa annua var. lanuginosa Sennen, Diagn. Nouv. sér. 1933: 209, n. 8980. 1936 Rif Orient.: 132. 1934, nom. nud., syn. nov. Poa annua var. pilantha Ronniger, Verh. Deutsch. Bot. Ges. Wien 88-89: 97. 1941.
Flowering. All year. Ecology. Pastures and grasslands along roads, fallow fields, gardens, margins of watercourses and more or less nitrified soils of all types; edaphically indifferent; 0−2100 m a.s.l.
Distribution Notes. Plants are found in the territory covered by Flora Iberica that have hairy lemmas, at least towards the internerval basal zone, with this indumentum being more perceptible in apical flowers of the spikelet. This characteristic is usually accompanied by a very dense silky indumentum in the veins. In other cases, the spikelet has lemmas with a glabrous internerval surface, usually accompanied by a lower density of indumentum in the nerves, with sometimes even the medium ones being glabrous or glabrescent. The first variation corresponds to Poa annua var. lanuginosa Sennen (Diagn. Nouv. sér. 1933: 209, n. 8980. 1936, a name that prevails over the name P. annua var. pilantha Ronninger (Verh. Deutsch. Bot. Ges. Wien 88-89: 97. 1941). When Scholz in Ber. Deutsch. Bot. Gesell. 81: 19 (1968) raised Ronninger's taxon to the subspecies category, he stated that the distribution of this subspecies was Mediterranean (e.g. Greece, Italy, Spain and Morocco) and extra-Mediterranean for the type subspecies. Although plants of Mediterranean environments in the Iberian Peninsula tend to have hairier lemmas, we have also found specimens assignable to var. annua and, conversely, we have observed plants with hairy lemmas in typically Eurosiberian areas (e.g. Lugo, Minho, Oviedo and Santander) and even Macaronesia (e.g. Madeira).
In certain populations, some spikelets are completely sterile and reduced to a set of whitish or hyaline membranes. Although infrequent, plants with loosely antrorsescabrid inflorescence branches have been detected, perhaps as a result of hybridisation with other species (e.g. MA 420475, MA 449625).
DNA sequence data support the hypothesis that P. annua, a tetraploid species, has arisen by hybridisation-and subsequent polyploidisation-between two Eurasian diploid species, the annual P. infirma Kunth and the rhizomatous perennial P. supina Schrad. (Soreng et al. 2010;Mao and Huff 2012), as suggested by Nannfeldt (1937).
Flowering. October to May (July). concinna Gaudin] in E Spain are mistaken, as this taxon is actually only distributed from SE France to the Balkan Peninsula. That taxon differs from P. bulbosa by their smaller sizes and narrower leaves, 0.8-2.2 mm ligules and never-proliferating spikelets with 6-10 flowers. In a few peninsular populations, plants with spikelets bearing 9-10 flowers have been detected, but they coincide with P. bulbosa in all other characters.
Caryopses are formed in this species, but sexual reproduction is infrequent; more common propagation routes include the formation of bulbs at the base of the plant or bulbils at the inflorescence level. This latter phenomenon, pseudovivipary, is extraordinarily frequent in P. bulbosa and involves the formation of bulbils for vegetative multiplication in the place of normal flowers ("proliferated spikelets"; Ofir and Kigel 2014). These bulbils may or may not coexist with normal flowers on the same spikelet or plant or in the same population. The balance between clonal and sexual reproduction is controlled mainly by day length and temperature; short days and low temperatures usually promote proliferating inflorescences, whereas long days and high temperatures induce normal and seminiferous ones. The proliferating spikelets usually carry (1-) 2-3 bulbils and have deformed floral parts: the glumes are usually narrower, the lemma is typically long (up to 20 mm), thin and either glabrous or only hairy on the central and marginal veins and the palea is missing or fully integrated into the bulbil, similar to the lodicules. Stamens are also missing or very reduced in size. The bulbils tolerate desiccation, are dormant during the summer and are dispersed by wind and ants. Both the basal bulbs, which are also dormant during the summer and the inflorescence bulbils sprout at the peak of the winter rainy season (cf. Ofir and Kigel 2014).
Two Bulbs appear to have arisen in Poa at least twice and possibly as many as four times (Cabi et al. 2016). Taxa having bulbs are distributed in four clades: (1) P. supersect. Poa

Conclusions
In the territory covered by Flora iberica, the genus Poa is represented by 24 taxa (17 species, 1 subspecies and 8 varieties), mostly perennial. The majority of these taxa have broad global and/or European distributions, whereas two (P. legionensis and P. minor subsp. nevadensis) are Spanish endemics and two have restricted distributions (P. ligulata, Iberian-North African; P. flaccidula, Iberian-North African and the Balearic Islands, extending to Provence, France). The most widely distributed species are P. bulbosa and P. annua, reflecting their worldwide range. The provinces with the greatest representation of Poa are Huesca, Santander, Lérida and Andorra, all located in the N Iberian Peninsula, which are traversed by mountain systems and subjected to a temperate climate.