﻿Revision of the genus Agrostis (Poaceae, Pooideae, Poeae) in Megamexico

﻿Abstract Agrostis is one of the most diverse genera of the Poaceae, including ca. 198 species, principally distributed in cold and temperate regions of the world, but also found in the high mountains of the tropics. We present a revision based on morphoanatomical evidence, for the biogeographic region known as Megamexico 3 (i.e., Mexico including the desert areas of southern USA and the Central America territory, to northern Nicaragua). We include taxonomic descriptions and an identification key for the found taxa, maps with the known geographical distribution of the species, and figures with the morphoanatomical characteristics, elevation and phenology. Agrostis is represented in the study zone by 20 species, of which four are endemic and three are introduced. Most records of the genus are distributed in the mountains, above 1500 m a.s.l., in open areas of temperate forests, with conifers and Quercus. Specimens with spikelets occur year round, but most records occur during the wet season, in the months of July to October. We propose a preliminary conservation assessment for each species in the study zone, according to the International Union for Conservation of Nature categories: one with Deficient Data (DD), six as Endangered (EN), two as Vulnerable (VU), and 11 as Least Concern (LC).


Introduction
The genus Agrostis L. includes ca. 198 species (Soreng et al. 2022), principally distributed in cold and temperate regions of the world, but also found in the high mountains of the tropics. The genus belongs to the subfamily Pooideae Benth., tribe Poeae R. Br., and subtribe Agrostidinae Fr. (Soreng et al. 2022). Agrostis species are characterized by the usually fragile habit of the plants, synflorescences of the panicle type, spikelets one-flowered, floret notably shorter than the glumes, usually 1/3-3/4 the length of the glumes, rarely longer, lemma with usually five nerves, palea often reduced or absent, and rachilla prolongation absent. Some of the species are forage plants of regular to excellent quality (Mejía-Saulés and Dávila 1992), while others are agricultural weeds, and some are excellent lawn grasses in cool climates (Harvey 2007).
The systematics of Agrostis has been considered as challenging, since the limits between this and other genera remain poorly understood, and there are several species complexes where the limits between taxa are difficult to establish due to morphological variation. Attempts at infrageneric classifications have been made in the past, based on the habit of the plants, presence of awns in the glumes and lemmas, and the presence of transversal thickenings in the outer walls of the lemma epidemal cells (called the "Trichodium net"), but some authors indicate that the established groups are unnatural (e.g. Clayton and Renvoize 1986). Several authors recognize at least two subgenera, on the basis of the absence (A. subg. Vilfa (Adans.) Rouy) or presence of paleas (A. subg. Agrostis). Peterson et al. (2020) provide a molecular phylogeny of some European species of Agrostis and allied genera, where two clades that correspond with these two groups are recovered. Studies of the genus that incorporate several lines of evidence are scarce, but some outstanding works are the ones of Björkman (1960), Carlbom (1967), Widén (1971) and Romero-García et al. (1988). Recent studies based on molecular evidence include some species of Agrostis, showing that the sampled species form a well-supported clade, including species of Bromidium Nees & Meyen, Chaetopogon Janch, Lachnagrostis Trin., and Polypogon Desf. (Saarela et al. 2010(Saarela et al. , 2017Tkach et al. 2020;Orton et al. 2021). Despite the existence of previous studies, the systematic knowledge of Agrostis has been far from ideal for decades, urging a worldwide revision of the genus (e.g., McVaugh 1983;Pohl and Davidse 1994).
Mexico is considered as a mega-diverse country, since 10-12% of the known species across the globe inhabit its territory (Llorente and Ocegueda 2008). In this country, ca. 23,314 native species of vascular plants have been reported, and a little more than half are endemic, which places Mexico in second position for endemism, after South Africa (Villaseñor 2016). Rzedowski (1991), based on the geographic affinities and endemism of the phanerogamic flora of Mexico, proposed three phytogeographic areas, which extend beyond the political limits of the country as follows: 1) Megamexico 1, which includes the Sonoran, Chihuahuan and Tamaulipan desert areas of the southern USA; 2) Megamexico 2, which includes the Centroamerican territory up to northern Nicaragua; 3) Megamexico 3, which includes the latter two (Fig. 1). This region has been recognized as a biodiversity hotspot and unique in its complex geology, orography, and its climatic heterogeneity (Rzedowski 1991;Ferrusquía-Villafranca 1993;García 2004).
One of the first taxonomic studies of Agrostis in Megamexico 3 was the work of Fournier (1886), where several species that are still accepted were described. Another pioneering work was from Hitchcock (1905), who studied the taxonomy of North American species of Agrostis. Years later, the same author provided a synopsis of the Mexican species of the genus (Hitchcock 1913). As part of North American Flora, Hitchcock (1937) updated and expanded his 1905 work. Several decades later, Beetle et al. (1983) provided a taxonomic revision of the Mexican species, but this work contains some errors and omissions (see Vigosa-Mercado 2022b), and since its publication, several of the included species have been transferred to other genera and new records have been made.
Other relevant works for Agrostis in Megamexico 3 are the catalogs of Mexican Poaceae species by Espejo-Serna et al. (2000), Dávila et al. (2006Dávila et al. ( , 2018, Villaseñor (2016) and Sánchez-Ken (2019). The genus has also been studied in state catalogs and regional floras, including the states of Chihuahua  (Acosta 2001) and the Valley of Tehuacán-Cuicatlán (Vigosa-Mercado 2017). Other works that partially cover Megamexico 3 are those of Harvey (2007), which is part of the Flora of North America North of Mexico, and Pohl and Davidse (1994), as part of the Flora Mesoamericana. In this study, we provide an updated review of the morphoanatomy, taxonomy, distribution, and conservation of Agrostis in Megamexico 3.
The analysis of the specimens consisted of: 1) verification of their correct identification, 2) correction of erroneous determinations, 3) updating of the names in synonymy, 4) identification of unnamed specimens, 5) taking measurements of vegetative and reproductive structures for descriptions, and 6) integration of information of the specimens in a database. The synonyms of some of the species are too extensive, whereby only the names with types collected in the study zone, or names widely used in the literature, are cited in the main text. A list of other heterotypic synonyms is provided in Suppl. material 1. Descriptions are based on the examined specimens from the study zone, but measurements reported in the literature from other regions (e.g., Harvey 2007), are included as comments, below the species descriptions. The descriptions of species with few herbarium specimens were complemented with information from the literature. Below the description of each species, one to three representative specimens per state are cited. A list of additional examined specimens is provided in Suppl. materials 2, 3.

Anatomical and micromorphological study
Samples of mature leaves and florets were taken from herbarium specimens, with prior authorization, except for species of which no physical herbarium specimens were seen, as A. idahoensis Nash. For each species, a variable number of specimens was studied according to the availability of material. Specimens studied for leaf anatomy are marked with one asterisk (*), and specimens studied for floret micromorphology are marked with two asterisks (**) in the lists of examined specimens.
Leaf blade samples were rehydrated with hot water for 1-5 minutes. The abaxial epidermis was isolated by removing the adaxial epidermis and underlying tissues with a razor blade. Hand transversal sections were taken with a razor blade from the upper third of the leaf blades. The isolated epidermis and transversal sections were treated with 6% sodium hypochlorite solution to clarify and soften the tissues, then washed with water. Only the transversal sections were stained with 1% safranin, and washed again. Both kinds of preparations were mounted with glycerin gelatin. For the description of the anatomical characteristics, the terminology proposed by Ellis (1976Ellis ( , 1979 was used with some modifications.
Floret samples were mounted in aluminum sample holders with conductive carbon tape, exposing the abaxial surface of the lemma, and covered with a layer of gold. The observation and taking of digital photographs were carried out in a Hitachi SU1510 scanning electron microscope.

Elevation and phenology histograms
Histograms of elevation and phenology were drawn in Microsoft Excel (Microsoft Corporation 2022), using the date of collection of the herbarium specimens, excluding duplicates. Phenology histograms represent both the presence of flowers and fruits, since spikelets in a synflorescence contain both kind of structures during the reproductive season. The Y axis in the graphs represents the proportion of the occurrences.

Distribution maps and conservation assessment.
Maps of known geographic distribution of Agrostis species, are based on the herbarium specimen data. Herbarium specimens examined were georeferenced by using either Google Earth online or Mapa digital de Mexico V. 6 [Digital Map of Mexico] (INEGI 2022). Maps were drawn using QGIS 3.22 (QGIS.org 2022). In the lists of examined specimens, coordinates georeferenced for the purposes of this work appear in square brackets. Records of distribution of Agrostis species in the study zone that we were unable to confirm, are discussed under each species description. These records were taken from several references (e.g., Villaseñor 2016;Dávila et al. 2018;Sánchez-Ken 2019), where no examined specimens are cited.
A preliminary conservation assessment in the study zone was proposed for each species, according to the International Union for Conservation of Nature categories and criteria B (IUCN 2012), as well as other sources of information, such as the size of populations indicated in the specimen labels, number of collections, and the presence of records in protected areas. The Extent of Occurrence (EOO), defined as the area contained within the shortest continuous imaginary boundary, which can be drawn to encompass all the known sites of present occurrence of a taxon, and the Area of Occupancy (AOO), defined as the area within the extent of occurrence which is occupied by a taxon (IUCN 2012), were calculated in km 2 , using the data from localities, in the R package ConR (Dauby 2020), assuming cells of 2 km per side.

Species concept and delimitation
In this work, the cohesive species concept (Templeton 1989) was followed as an explanatory hypothesis to recognize species and infraspecific categories. This concept has a population genetics framework, but does not discard other cohesive factors to explain species or infraspecific taxa recognition, such as the expression of morphology (phenotypic variability constraints on individuals in the group) and habitat distinctiveness (geographic distribution and ecological constraints). Evolutionary processes act on these cohesive factors to maintain populations or generate new taxa. Species recognized here are characterized by a combination of characters, evaluated in most cases in a broad study of herbarium specimens and the individuals in the field, as well as the known distribution of the organism.

Diversity, elevation, habitat, and phenology
The genus Agrostis is represented in Megamexico 3 by 20 species (Table 1), of which four are endemic and three are introduced. We include a list of 16 excluded names of Agrostis, previously reported in the study zone, at the end of the work. The found species are distributed mainly in the mountains of southwestern USA, Mexico and Central America, between 14-4,520 m a.s.l. (Fig. 9A). The mean elevation of the records is 2,544.5 m, and the median is 2,592 m. The species grow in a wide range of habitats, such as grasslands, shrublands, stream edges, and temperate forests. Most records of native species of Agrostis are distributed above 1,500 m a.s.l. (Fig. 9B), usually in open areas of temperate forests, with conifers and Quercus. Some species, such as Agrostis microphylla (Fig. 9N), A. pallens (Fig. 9O), as well as the populations in the southwestern USA of A. exarata (Fig. 9H), A. hyemalis (Fig. 9K), A. perennans (Fig. 27A), and A. scabra (Fig. 27B), are distributed at lower elevations, often in drier environments. Introduced species are distributed between 651-3300 m a.s.l. (Fig. 9C) and seem to prefer disturbed habitats. They are found mainly in moist soils of ditches, marshy habitats, and stream edges. Specimens with flowers and fruits occur all year round, but most records are during the wet season (Fig. 10A), between the months of July to October. Records of native species of Agrostis show the same pattern (Fig. 10B), while specimens of introduced species are found during the months of June to December and no specimens of introduced species were found from January to May (Fig. 10C). Elevation, habitat, and phenology for each species are discussed under each species description.

Distribution
Distribution of most found species extend beyond the study zone, and there are several main patterns of the native species: 1) species widely distributed in the Americas (A. hyemalis, A. perennans, A. scabra); 2) species widely distributed in North America, with a southern distribution limit in southwestern USA (A. elliottiana, A. idahoensis); 3) species distributed from Alaska to central Mexico (A. exarata); 4) species distributed from Canada to Baja California peninsula (A. microphylla, A. pallens, A. variabilis); 5) species distributed from northern Mexico to South America (A. tolucensis); 6) species distributed from central or southern Mexico to Central America (A. ghiesbreghtii, A. laxissima, A. subpatens, A. turrialbae); and 7) species distributed in central Mexico (A. bourgaei, A. calderoniae). Agrostis subrepens is an outlier by its disjunct distribution in Chihuahua, Mexico, and South America. Table 1 shows the distribution of the species in Megamexico 3. Distribution for each species is discussed under each species description.

Taxonomy
The two subgenera of Agrostis are represented in the study zone. The three introduced species belong to subgenus Vilfa (A. capillaris, A. gigantea, A. stolonifera), characterized by the stoloniferous or rhizomatous habit of the plants, spikelets with a usually well-developed palea, reaching (1/5-)1/3-3/4 of the lemma length, and epidermal cells of the lemmas without transversal thickenings. The remaining species belong to subgenus Agrostis, characterized by the usually caespitose habit of the plants, spikelets with usually reduced palea, less than 1/5 of the lemma length, and epidermal cells of the lemmas with transversal thickenings.
In the subgenus Agrostis, there are several informal groups of morphologically similar species, where the taxonomy is often complex, since the differences between the species are often subtle and intermediate forms are common. However, through a combination of characters, a reasonably good separation can be made. These groups are: 1) species with usually open panicles and usually awnless lemmas (A. bourgaei, A. calderoniae, A. ghiesbreghtii, A. hyemalis, A. laxissima, A. idahoensis, A. perennans sensu lato, A. scabra, A. subrepens, A. turrialbae); 2) species with usually narrow and dense panicles, and often acuminate to awned glumes (A. exarata, A. microphylla, this group is called the A. exarata complex by Carlbom (1967)); 3) species with mostly basal leaves, usually conduplicated to convolute leaf blades, and usually narrow and dense panicles (A. subpatens, A. tolucensis, A. variabilis). Particularly challenging is the taxonomy of Agrostis perennans sensu lato (see Sylvester et al. 2020a), where numerous entities have been identified under this name. There is still much work to do on the taxonomy of Agrostis, and molecular evidence may help in the systematics of the group (Vigosa-Mercado in prep.).

Conservation status
We propose a preliminary conservation assessment for each species in the study zone (

Morphoanatomy
A general morphoanatomical characterization of the species found in the study zone is presented below. Description of the morphology and anatomy of each species is presented in the taxonomic treatment.
Habit. All the species of Agrostis in the study zone are herbaceous plants, usually perennial, but some annual species occur (A. elliottiana, A. microphylla). Most species are caespitose, with the culms growing densely in tufts, some species develop stolons (A. stolonifera, Fig. 33A; rarely A. capillaris and A. gigantea), rhizomes (A. capillaris, A. capillaris, A. gigantea, A. tolucensis, rarely A. exarata), or pseudostolons that have the appearance of rhizomes on herbarium specimens (A. perennans sensu lato, A. subrepens, Fig. 35B). Usually, the species in the study zone develop extravaginal tillers that are covered with cataphylls. While the type of tillering has been considered as a character of taxonomic importance (Philipson 1937;Widén 1971), this character is difficult to observe on herbarium specimens.
Roots. They are fibrous, and the presence of arbuscular mycorrhiza has been reported in Agrostis capillaris (Gollotte et al. 2004).
Culms. They are unbranched, hollow, and usually erect, but sometimes are decumbent in the lower portion. The length of the culms is variable, from a few centimeters to 1.2 meters in some species (A. gigantea). The number of nodes is variable, from one to several.
Leaves. They are formed by the sheath, leaf blade and ligule. They could be basal (Fig. 38A), cauline (Fig. 24A), or both, as in most species of Megamexico 3.
Sheaths. They are tubular. Their margins are free and clasp the culms. In the species of the study zone, the sheaths range from shorter to longer than the internodes, and their abaxial surface are glabrous or scaberulous.
Ligules. The length and form of the ligules have been recognized as a valuable taxonomic character (Philipson 1937;Widén 1971;Romero-García et al. 1988). In the species of the study zone, the ligules are variable, but in most cases no significant differences were found between the species. The ligules range from longer or shorter than wide, their abaxial surfaces are usually scaberulous, and the apices are acute, erose or truncate. In several species of Megamexico 3, the old ligules are often lacerate (e.g., A. bourgaei, Fig. 3B).
Leaf blade abaxial epidermis. Among the species in the study zone, the abaxial epidermis is quite homogeneous and thus its taxonomic value is poor, as previously noted by Romero- García et al. (1988).
The abaxial epidermis presents two differentiated regions, the intercostal and costal zones ( Fig. 2A). The intercostal zone is made up of elongated cells of constant shape and size, their walls are straight, the sidewalls are angled outwards, and end walls are vertical or angled (Fig. 2B). In the intercostal zone there are one or two rows of stomata ( Fig. 2A), with guard cells parallel-sided or low dome-shaped. No short cells were seen in the intercostal zone of the studied species. The costal zone presents elongated cells similar to the intercostal zone, but sometimes their walls are slightly thickened, with short cells (Fig. 2B), and silica bodies. Prickle hairs are present on both zones ( Fig. 2A). They are medium sized, with a short and raised barb. No micro or macrohairs were seen in the abaxial epidermis of the studied species.
Leaf blade transversal section anatomy. The leaf blades of Agrostis species display a no-Kranz anatomy (C3 photosynthesis). The anatomical features of the leaf blade have been considered of taxonomic importance, particularly the patterns of sclerenchyma distribution (Romero- García et al. 1988). In the studied species, leaf blade anatomy is a useful character for distinguishing some species, but several species share similar attributes.
A keel with several vascular bundles and parenchyma was found only in some individuals of A. exarata (Fig. 15A). There are one to three vascular bundles of second order between the bundles of first order, where all of them are at the same level, closer to the abaxial surface (Figs 6,15,22,31,37), and their shape is circular (Fig. 6B) to slightly elliptical (Fig. 31B). Sometimes there are third order vascular bundles, between the first and second order bundles, or near the leaf blade margins (Figs 6D, 22F). There are two sheaths surrounding the vascular bundles, an outer parenchymatous sheath that is interrupted abaxially (Fig. 15B), or sometimes also adaxially (Fig. 31E), and an inner sclerenchymatous complete sheath (Fig. 15J). Sclerenchyma is found associated with vascular bundles of first and second order, in abaxial or adaxial strands or girders (Figs 6,15,22,31,37). There are small caps of sclerenchyma in leaf margins (Fig. 22F). In some species, abaxial strands of sclerenchyma between the vascular bundles are found (Fig. 6E), and only in some individuals of A. ghiesbreghtii a hypodermal abaxial layer of sclerenchyma is detected (Fig. 15D, E).
The mesophyll is non-radiate, with regular small cells, isodiametric, and tightly packed (Fig. 6G). Colorless cells were found associated with the outer bundle sheath, only in some individuals of A. exarata (Fig. 15A). In all species, there are fan-shaped groups of small, bulliform cells in the base of adaxial furrows ( Fig. 6E), but sometimes in dried specimens they could be collapsed. In all species, there are prickle hairs in adaxial and abaxial epidermis.
Spikelets. They are small, no more than 4.5 mm long. They are made up of two basal bracts called glumes and a single floret (Fig. 3C). The florets consist of a lower bract called the lemma, an upper bract called the palea, and a bisexual flower (Fig. 3E). The base of the floret is slightly hardened (callus), usually with two tufts of hairs (Figs 5,30).
Glumes. They are longer than the floret, equal to unequal in size between them and keeled on the back. Their apices are usually acute to acuminate (Fig. 14C), or sometimes awned (A. microphylla, Fig. 23C; sometimes A. exarata).
Their consistency is membranous, with a single vein, and are scaberulous on the keel (Fig. 19D), and sometimes in the rest of the body. It has been considered that the glumes do not have characters of taxonomic value (Widén 1971).
Lemma micromorphology. Transversal thickenings in the outer walls of the abaxial epidermis cells, especially the ones of the lower half portion, could form a pattern that has been called the Trichodium net. It has been noted that this character is useful to form broad groups, and it has been proposed that it is an important character for the infrageneric classification of the genus (Björkman 1960;Widén 1971;Romero-García et al. 1988). Widén (1971) has recognized seven types of net, based on the width of the transversal thickenings. In the studied species of Agrostis, taxa with absent or reduced paleas have a conspicuous net, while the species with paleate spikelets usually lack, or have fragmentary nets (Figs 7,32), as noted in previous studies (Björkman 1960;Widén 1971;Romero-García et al. 1988). In the species of Agrostis present in Megamexico 3, it has also been found that this character is useful for distinguishing some morphologically similar species that are often confused (e.g., A. bourgaei and A. gigantea).
Flowers. They consist of a perianth with two scales (lodicules), an androecium of three stamens (one in A. elliottiana), and a unilocular gynoecium with two styles and two plumose stigmas.
Commentaries. The name Agrostis was first described in the work of Linnaeus, Genera Plantarum (Linnaeus 1737: 19), with a Latin diagnosis. According to the International Code of Nomenclature for Algae, Fungi and Plants (Art. 13.1) (Turland et al. 2018), the beginning of effective publication dates for generic names is 1 st May 1753, with the publication of Species Plantarum (Linnaeus 1753). In this latter work, Linnaeus described 12 names, classified in two groups: 1) Aristatae (A. spica-venti L., A. miliacea L., A. arundinacea L., A. rubra L., A. canina L., A. paradoxa L.); and 2) Muticae (A. stolonifera L., A. capillaris L., A. alba L., A. minima L., A. virginica L., A. indica L.). No type species was designated by Linnaeus. Hitchcock (1905) designated A. alba as the type, but the original material of this name is a Poa L. species (Widén, 1971), and the adoption of this name as lectotype would result in Agrostis becoming a synonym of Poa (McNeill et al. 1987). Years later, Hitchcock (1920), proposed A. stolonifera as lectotype, but this name conflicts with the original description of the genus, since it mentions that the lemmas are awned (Linnaeus 1737), and the original description of A. stolonifera mentions that the lemmas are unawned (Linnaeus 1753). Philipson (1937) was the first to propose as lectotype the name A. canina. Widén (1971) agreed with that choice, and formally designated this name, since it is the one that keeps better the usage of the generic name. Jarvis (1992) proposed the conservation of the name Agrostis, with a conserved type.
The species of this genus are often confused with other genera found in the study zone, with one-flowered spikelets, such as Lachnagrostis Trin., Muhlenbergia Scherb., Podagrostis (Griseb.) Scribn. & Merr., Polypogon Desf., Sporobolus R. Br., and some species of Peyritschia E. Fourn., but it is distinguished from them by the following combination of characters: spikelets disarticulating above the glumes, florets shorter than the glumes, usually 1/3-3/4 the length of the glumes, rarely longer, lemmas with usually five veins, dorsal awns often present, palea often reduced or absent (sometimes reaching up to 3/4 of the lemma length), and rachilla not prolonged. See the work of Sylvester et al. (2020b) for a key to differentiate Agrostis from morphologically similar genera.
Anatomy and micromorphology. Leaf blades flat in transversal section; adaxial furrows medium-sized, wide; adaxial ribs rounded; keel absent; first order bundles circular in outline, sheath interrupted adaxially and abaxially, abaxial and adaxial sclerenchyma in girders, narrowing towards the bundle; second order bundles circular in outline, sheath interrupted abaxially, abaxial sclerenchyma in girders, narrowing towards the bundle, adaxial sclerenchyma in strands or t-shaped girders; intercostal sclerenchyma absent; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells absent ( Fig. 6A-C). Lemmas with transversal thickenings polygonal, wider than the unthickened portions of the wall; prickle hairs scarce (Fig. 7A).
Distribution and habitat. Endemic. Herbarium specimens of A. bourgaei have been collected in Mexico City and the Mexican states of Hidalgo, México, Michoacán, Morelos, Puebla, and Oaxaca (Fig. 8A). The species has also been reported for Durango, Guanajuato, Querétaro, Tlaxcala, and Veracruz (Villaseñor 2016;Dávila et al. 2018;Sánchez-Ken 2019), but no specimens from these states were seen. Agrostis bourgaei is mainly found on edges of streams and moist soils, in open areas of conifer forests of the Trans-Mexican Volcanic Belt, between 1800-3800 m a.s.l., with some outliers in Morelos found lower, at 725 m a.s.l. (Fig. 9D).
Phenology. Specimens with spikelets have been collected from June to February, but most of the records are from August (Fig. 10D).
Commentaries. Agrostis bourgaei is similar to A. gigantea, and both are often confused. They share very similar leaf anatomy and paleate spikelets, but A. bourgaei is distinguished from the latter in the much more fragile aspect of the plants, caespitose habit, lateral branches of the panicle without spikelets near their base, lemmas with prickle hairs, transversal thickenings, and shorter paleas of up to 0.7(-1) mm long (vs. robust plants, usually rhizomatous habit, often some inferior branches with spikelets near their base, lemmas glabrous, without transversal thickenings, paleas up to 1.2 mm long in A. gigantea). The specimen García-Mendoza 1116 (MEXU) from Oaxaca lacks vegetative parts that may allow a more acceptable identification, but is included tentatively in this species for its paleate spikelets.
Conservation status. Agrostis bourgaei is an abundant and widespread species in Central Mexico. It is represented by 61 collections, with several populations occurring in 13 protected areas. The EOO is 45,765 km 2 and the AOO is 1,476 km 2 . Following the IUCN criteria, the preliminary assessment category is Least Concern (LC).
Representative specimens examined.
Anatomy and micromorphology. Leaf blades convolute or v-shaped in transversal section; adaxial furrows deep, narrow; adaxial ribs rounded to triangular; keel absent; first order bundles circular in outline, sheath interrupted abaxially, abaxial sclerenchyma in strands or girders in the central bundle, narrowing towards the bundle, adaxial sclerenchyma in strands; second order bundles circular in outline, sheath not interrupted, abaxial and adaxial sclerenchyma; intercostal sclerenchyma present, abaxial; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells absent (Fig. 6D, E). Lemmas with transversal thickenings irregular, wider than the unthickened portions of the wall; prickle hairs abundant (Fig. 7B).
Distribution and habitat. Endemic. Agrostis calderoniae has only been collected in the western slope of the Iztaccíhuatl volcano, in the state of México (Fig. 8B). This species grows in moist soils near the edge of streams, in open areas of temperate forests with Pinus, between 3500-3800 m a.s.l. (Fig. 9E).
Phenology. Specimens with spikelets have been collected in January, July, and August (Fig. 10E).
Commentaries. This species is similar to A. bourgaei, in the caespitose habit and paleate spikelets, but it is distinguished in the mostly basal leaves, leaf blades conduplicate or convolute, with deep adaxial furrows, abaxial intercostal sclerenchyma, longer spikelets of 2.5-3.5 mm long, and lemmas with transversal thickenings of irregular shape (vs. basal and cauline leaves, leaf blades flat, with medium-sized adaxial furrows, without intercostal sclerenchyma, spikelets of 2-2.7 mm long, lemmas with polygonal transversal thickenings in A. bourgaei).
Distribution and habitat. Introduced. Agrostis capillaris is native to Europe. This species has been collected in Francisco Morazán, Honduras, and in the state of México, Mexico (Fig. 8C). It grows in cloud forests and Pinus forests, at 2000-2830 m a.s.l. (Fig. 9F).
Phenology. Specimens with spikelets have been collected in June (Fig. 10F).
Commentaries. This species is often confused with A. castellana (see notes under excluded species). Some individuals of A. capillaris can develop ligules of the flowering culms longer than wide.
Distribution and habitat. Agrostis elliottiana is native to North America, distributed on the East Coast of USA, from Pennsylvania to Florida, and from northern California to Texas (Harvey 2007). Herbarium specimens from the study zone of this species have been collected in southern Arizona and New Mexico, USA (Fig. 8D). Agrostis elliottiana has also been reported from the Mexican state of Yucatán (Beetle et al. 1983), but herbarium specimens associated with this record have not been found. This species grows in the edges of streams, in the middle of scrublands, with Arctostaphylos and Juniperus, between 1189-1676 m a.s.l. (Fig. 9G). There are more records of this species in the study zone, on databases (GBIF 2023a), but not all of them have images, and thus we were unable to confirm their identity.
Phenology. Specimens with spikelets have been collected in April (Fig. 10G). Commentaries. Agrostis elliottiana is often confused with A. hyemalis but differs from it in the annual habit of the plants, leaf blades sometimes conduplicated, with triangular adaxial ribs and abaxial intercostal sclerenchyma, spikelets not clustered, lemmas with a flexuous awn, and only one anther (vs. perennial plants, leaf blades flat, with rounded abaxial ribs, without intercostal sclerenchyma, spikelets clustered at branch tips, lemmas unawned, three anthers in A. hyemalis).
Anatomy and micromorphology. Leaf blades flat in transversal section; adaxial furrows deep, narrow; adaxial ribs rounded; keel sometimes present, with three vascular bundles; first order bundles circular in outline, sheath interrupted abaxially, abaxial and adaxial sclerenchyma in girders, narrowing towards the bundle; second order bundles circular in outline, sheath interrupted abaxially, abaxial sclerenchyma in girders, narrowing towards the bundle, adaxial sclerenchyma in strands; intercostal sclerenchyma absent; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells present, associated with first and second order vascular bundles ( Fig. 15A-C). Lemmas with transversal thickenings polygonal, wider than the unthickened portions of the wall; prickle hairs absent or scarce (Fig. 7E).
Distribution and habitat. Agrostis exarata is distributed from Alaska to central Mexico, and is also found in Kamchatka and the Kuril Islands (Harvey 2007). In the study zone, this species has been collected in the USA states of Arizona, California, New Mexico and Texas, and in the Mexican states of Baja California, Baja California Sur, Chihuahua, Coahuila, Durango, Guanajuato, Hidalgo and Sonora (Fig. 8E). It has also been reported from Mexico City and the Mexican states of México and Puebla (Villaseñor 2016;Sánchez-Ken 2019), but no specimens from these states were seen. It grows in moist soils of stream edges and lake margins, in open areas of temperate forests with Pinus or Quercus, and shrublands, between 350-2900 m a.s.l. (Fig. 9H). The USA and Baja California populations of this species grow in lower elevations than the southern ones.
Phenology. Specimens with spikelets have been collected from April to November (Fig. 10H).
Commentaries. For other regions it has been reported that the panicles can reach 4 cm wide, and paleas up to 0.5 mm long (Harvey 2007).
Agrostis exarata is a variable species. Several specific names or infraspecific taxa have been proposed, but none of them are recognized in this work. Mexican populations of this species have been called A. durangensis, and are characterized by the unawned lemmas, and the presence of a short, veinless palea, but these characters overlap with populations of other regions. Agrostis exarata is often confused with several Polypogon species, which are often sympatric, but differs from them in the spikelets disarticulating above the glumes (vs. disarticulation below the glumes, with a pedicel fragment). Mexican populations of A. exarata are sometimes confused with some individuals of A. tolucensis with wide leaf blades, but differ from it in the spikelets often with a palea, and lemma usually unawned (vs. spikelets without a palea, lemma awned in A. tolucensis). This species is also confused with A. blasdalei and A. densiflora (see the notes in excluded species).
Conservation status. Agrostis exarata is a widespread species in the study zone. It is represented by 61 collections, with several populations occurring in 13 protected areas. The EOO is 1,402,821 km 2 and the AOO is 188 km 2 . Following the IUCN criteria, the preliminary assessment category is Least Concern (LC).
Leaf anatomy. Leaf blades convolute, rarely flat in transversal section; adaxial furrows deep, narrow; adaxial ribs rounded; keel absent; first order bundles circular in outline, sheath interrupted adaxially and abaxially, abaxial and adaxial sclerenchyma in girders; second order bundles circular in outline, sheath interrupted abaxially, abaxial sclerenchyma in girders, narrowing towards the bundle, adaxial sclerenchyma in strands; intercostal sclerenchyma usually present, a hypodermal band, sometimes absent; leaf margins with sclerenchyma continuous with the hypodermal band; colorless cells absent (Fig. 15D, E). Lemmas with transversal thickenings oblong, wider than the unthickened portions of the wall; prickle hairs abundant (Fig. 7F).
Distribution and habitat. Endemic. Agrostis ghiesbreghtii is distributed from central Mexico to Guatemala. In Mexico, it has been collected in Mexico City and the states of Chiapas, Guanajuato, Guerrero, Hidalgo, México, Michoacán, Morelos, Oaxaca, Puebla and Veracruz (Fig. 8F). It is also reported from Chihuahua and Durango (Sánchez-Ken 2019), but no specimens from these states were seen. In Guatemala, it has been collected in the departments of Quetzaltenango and Sacatepéquez. This species grows in open areas of temperate forests, with Abies, Pinus, Quercus, and alpine grasslands, between 1110-3700 m a.s.l. (Fig. 9I).
Phenology. Flowering and fruiting specimens have been collected year round, but most of them between the months of August and February (Fig. 10I).
Commentaries. This species is similar to A. laxissima in the open panicles, awned lemmas and lemma micromorphological features, but it is distinguished in the leaf blades stiffer, usually convolute or involute, with deep adaxial furrows and usually with a hypodermal bland of abaxial sclerenchyma, and usually larger spikelets of (2.5-)3-4 mm long (vs. leaf blades lax, flat, with medium-sized adaxial furrows, without intercostal sclerenchyma, spikelets of 1.7-3 mm long in A. laxissima). Some specimens with unusually wide and flat upper leaf blades have been collected in Guerrero and Chiapas, but the other characters are congruent with A. ghiesbreghtii. This species is also very similar to A. mertensii, and more studies are needed to define its taxonomic boundaries (see the notes in excluded species).
Anatomy and micromorphology. Leaf blades flat in transversal section; adaxial furrows medium-sized, wide; adaxial ribs rounded; keel absent; first order bundles circular in outline, sheath interrupted adaxially and abaxially, abaxial and adaxial sclerenchyma in girders, narrowing towards the bundle; second order bundles circular in outline, sheath interrupted adaxially and abaxially, abaxial and adaxial sclerenchyma in girders, narrowing towards the bundle; intercostal sclerenchyma absent; leaf margins with small to well-developed sclerenchyma caps, rounded; colorless cells absent (Fig. 15F-H). Lemmas without transversal thickenings, or these poorly developed; prickle hairs absent or scarce (Fig. 7G).

Distribution and habitat. Introduced. Agrostis gigantea is native to Eurasia.
In the study zone, it has been collected in the USA states of Arizona, California, New Mexico, Texas, and in Mexico City, and the Mexican states of Durango, México, Michoacán, San Luis Potosí, and Sonora (Fig. 18A). This species has also been reported from Guanajuato, Morelos, and Oaxaca (Sánchez-Ken 2019), but no specimens from these states were found. Agrostis gigantea grows in disturbed areas, mainly in moist soils of ditches, marshy places and stream edges, between 651-3300 m a.s.l. (Fig. 9J).
Phenology. Specimens with spikelets have been collected from June to December (Fig. 10J).
Commentaries. It has been reported for other regions that the blades can reach 12 mm wide, spikelets up to 3.2 mm long and lemmas up to 2.2 mm long (Harvey 2007). This species is often confused with A. bourgaei (see the note under the description of that species). Agrostis gigantea also is similar to A. stolonifera in the paleate spikelets, but differs from it in the rhizomatous habit of the plants and more open panicle (vs. stoloniferous plants, panicle usually contracted in A. stolonifera).
The rhizomatous plants of Agrostis, with paleate spikelets, were formerly known as A. alba L., a name that was described without a type designation (Linnaeus 1753). Hitchcock (1905) considered the specimen LINN 84.23 as the type, but this was received by Linnaeus long after 1753 (Jarvis 2007). Widén (1971) indicates that this name must be typified by a specimen at the Van Royen Herbarium (L0052692), since A. alba was based on the work of Royen (1740), but that specimen corresponds to Poa nemoralis L., so currently A. alba is a synonym of the latter.
Conservation status. Since Agrostis gigantea is an introduced species in the study zone, its conservation status is considered as Least Concern (LC).
Anatomy and micromorphology. Leaf blades flat in transversal section; adaxial furrows medium-sized, wide; adaxial ribs rounded; keel absent; first order bundles circular in outline, sheath interrupted adaxially and abaxially, abaxial and adaxial sclerenchyma in girders, narrowing towards the bundle; second order bundles circular in outline, sheath interrupted abaxially, abaxial sclerenchyma absent or in girders, narrowing towards the bundle, adaxial sclerenchyma absent or in strands; intercostal sclerenchyma absent; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells absent (Fig. 15I-K). Lemmas with transversal thickenings oblong, wider than the unthickened portions of the wall; prickle hairs abundant to scarce (Fig. 7H).
Distribution and habitat. Agrostis hyemalis is distributed from Ontario province in Canada to central Mexico, and is also present in the West Indies and Ecuador (Harvey 2007). The records of this species in western North America could represent the confusion with A. scabra (see note below). It has also been reported from Perú (Soreng and Peterson 2003). In the study zone, this species has been collected in southern Arizona and Texas, USA, and in the Mexican states of Aguascalientes, Baja California, Baja California Sur, Chihuahua, Coahuila, Durango, Hidalgo, Jalisco, México, Michoacán, Puebla, Querétaro, San Luis Potosí and Sonora (Fig. 18B). It has also been reported from the Mexico City and the states of Colima, Guanajuato, Morelos, Nuevo Leon, Oaxaca, Sinaloa, Tlaxcala and Veracruz (Villaseñor 2016), but no specimens from these states were found. Agrostis hyemalis grows in open areas of temperate forests, with Abies, Juniperus, Pinus or Quercus, cloud forests, rocky areas of grasslands and stream edges, between 14-2710 m a.s.l. (Fig. 9K). The Texan populations of this species grow in lower elevations than the Mexican ones.
Phenology. Specimens with spikelets have been collected from January to November, but most of the records are from May (Fig. 10K).
Commentaries. It has been reported for other regions that the panicles can reach 36 cm long (Harvey 2007).
Agrostis hyemalis is often confused with A. elliottiana (see the note under the description of that species). It is also similar to A. scabra, in the panicle branches rebranching in the upper third and somewhat clustered spikelets, and also shares several leaf blade anatomy features. Agrostis hyemalis differs from the latter in the culms with usually more than three nodes, basal and cauline leaves, more clustered and shorter spikelets, of 1-2(-2.5) mm long, and smaller anthers of 0.2-0.5 mm long (vs. culms with usually 1-2(-3) nodes, usually mostly basal leaves, spikelets of 2-3(-3.4) mm long, anthers 0.5-1.4 mm long in A. scabra). The identification of these two species is especially difficult if the plants are not collected with the basal parts.
Conservation status. Agrostis hyemalis is a widespread species in the study zone. It is represented by 86 collections, with several populations occurring in 15 protected areas. The EOO is 1,491,700 km 2 and the AOO is 248 km 2 . Following the IUCN criteria, the preliminary assessment category is Least Concern (LC).
Anatomy and micromorphology. Not seen. Distribution and habitat. Agrostis idahoensis is distributed from Alaska to California and New Mexico (Harvey 2007). It is also present in Chile and Argentina (Rúgolo and Molina 1997). In the study zone, this species has been collected in southern Arizona and California (Fig. 18C). It grows in stream edges of temperate forests, with Abies, Arctostaphylos, Picea or Pinus, between 3084-3121 m a.s.l. (Fig. 9L). There are more records of this species in the study zone, on databases (GBIF 2023b), but not all of them have images, and thus we were unable to confirm their identity.
Phenology. Specimens with spikelets have been collected in July and August (Fig. 10L).
Commentaries. Agrostis idahoensis is similar to A. perennans sensu lato. It differs from it in the mostly basal leaves, persistent, with leaf blades 0.5-2 mm wide (vs. basal and cauline leaves, the basal ones often drying before anthesis, with leaf blades often more than 2 mm wide in A. perennans). It is also similar to A. scabra, from which it differs in the branches of the panicle rebranching about or slightly above mid-length, and spikelets not clustered at the branch tips (vs. branches rebranching in the upper third, spikelets somewhat clustered in A. scabra). Agrostis idahoensis is scarcely different from A. turrialbae, distributed from central Mexico to Central America. The former differs in flatter and wider leaf blades, 0.5-2 mm wide (vs. conduplicate or involute leaf blades, 0.3-0.5 mm wide in A. turrialbae).

Agrostis laxissima
Anatomy and micromorphology. Leaf blades flat in transversal section; adaxial furrows medium-sized, wide; adaxial ribs rounded; keel absent; first order bundles circular in outline, sheath interrupted abaxially, abaxial sclerenchyma in girders, narrowing towards the bundle, adaxial sclerenchyma in strands; second order bundles circular in outline, sheath interrupted abaxially, abaxial sclerenchyma in girders, narrowing towards the bundle, adaxial sclerenchyma in strands; intercostal sclerenchyma present, abaxial; leaf margins with well-developed sclerenchyma caps, extending along abaxial side of the leaf; colorless cells absent (Fig. 22A-C). Lemmas with transversal thickenings irregular to oblong, wider than the unthickened portions of the wall; prickle hairs abundant (Fig. 7I).

Distribution and habitat. Endemic. Agrostis laxissima is distributed from
Southern Mexico to Guatemala (Pohl and Davidse 1994). It has also been reported in Honduras (Soreng and Peterson 2003). This species has been collected from the Mexican state of Chiapas, and the departments of Quezaltenango, Sacatepéquez, San Marcos and Solola in Guatemala (Fig. 18D). Agrostis laxissima grows in temperate forests, with Abies, Pinus, or Quercus, in cloud forests and grasslands, between 2250-3200 m a.s.l. (Fig. 9M).
Phenology. Specimens with spikelets have been collected from June to March, but most of the records are from December and January (Fig. 10M).
Commentaries. Agrostis laxissima is often confused with A. ghiesbreghtii (see the note under the description of that species).
Conservation status. Agrostis laxissima is only known from a few localities of southern Mexico and Guatemala. It is represented by 17 collections, with several populations occurring in six protected areas. The EOO is 2,615 km 2 and the AOO is 44 km 2 . Following the IUCN criteria, the preliminary assessment category is Vulnerable (VU).
Anatomy and micromorphology. Leaf blades flat in transversal section; adaxial furrows shallow, wide; adaxial ribs rounded; keel absent; first order bundles circular in outline, sheath interrupted adaxially and abaxially, abaxial and adaxial sclerenchyma in girders, narrowing towards the bundle; second order bundles circular in outline, sheath interrupted abaxially, abaxial and adaxial sclerenchyma in strands; intercostal sclerenchyma absent; leaf margins with small sclerenchyma caps, rounded; colorless cells absent (Fig. 22D-F). Lemmas with transversal thickenings irregular to oblong, wider than the unthickened portions of the wall; prickle hairs scarce to abundant (Fig. 7J).
Distribution and habitat. Agrostis microphylla is distributed from British Columbia, Canada, to the northern peninsula of Baja California, Mexico (Harvey 2007). In the study zone, this species has been collected in the Mexican state of Baja California (Fig. 18E), where it grows in stream edges and vernal pools, between 37-315 m a.s.l. (Fig. 9N). It has also been reported from the state of Baja California Sur, but the database record linked to this report has no images (GBIF 2023c), and thus we were unable to confirm its identity.
Phenology. Specimens with spikelets have been collected from April to June (Fig. 10N).
Commentaries. It has been reported for other regions that the culms can reach 45 cm long, panicles up to 12 cm long, spikelets up to 5 mm, and awns up to 8 mm (Harvey 2007).
Agrostis microphylla is one of the few annual Agrostis species. It is often confused with the smaller forms of A. exarata, from which it differs in the annual habit, spikelets of 3-4.5 mm long and lemmas with an awn of 3.5-6 mm long (vs. perennial plants, spikelets of 2-2.5 mm, lemmas unawned or with an awn up to 3 mm long in A. exarata), as well as the leaf blade anatomy and lemma micromorphology.
Anatomy and micromorphology. Leaf blades flat in transversal section; adaxial furrows deep, narrow; adaxial ribs rounded; keel absent; first order bundles circular in outline, sheath interrupted adaxially and abaxially, abaxial sclerenchyma in strands or girders, narrowing towards the bundle, adaxial scleren- chyma in strands or t-shaped girders; second order bundles circular in outline, sheath interrupted abaxially, abaxial and adaxial sclerenchyma in strands; intercostal sclerenchyma absent; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells absent (Fig. 22G-I). Lemmas with transversal thickenings polygonal, wider than the unthickened portions of the wall; prickle hairs abundant (Fig. 7K).
Distribution and habitat. Agrostis pallens is distributed from British Columbia, Canada, to Baja California, Mexico, and is also present in Montana and Utah (Harvey 2007). In the study zone, this species has been collected in southern California and the Mexican state of Baja California (Fig. 18F). It grows in coastal sands, stream edges, temperate forests with Pinus or Quercus, and xeric shrublands, between 40-1635 m a.s.l. (Fig. 9O).
Phenology. Specimens with spikelets have been collected from June to August (Fig. 10O).
Commentaries. It has been reported for other regions that panicles can reach 6(-8) cm wide (Harvey 2007).
The Mexican populations of A. pallens have lemmas with longer awns, up to 2.5 mm long, than those of southern California, but the other characters are congruent with the previous descriptions of this species. The plants of lower elevations have more contracted panicles than those of higher elevations, as noted previously by Harvey (2007). Plants of lower elevations are often confused with A. exarata, from which they differ in the rhizomatous habit, mostly cauline leaves, and palea absent or up to 0.2 mm long (vs. usually caespitose habit, basal and cauline leaves, palea often present, up to 0.8 mm long in A. exarata).
Conservation status. Agrostis pallens is apparently a rare species in the study zone. It is represented by 12 collections, with several populations occurring in four protected areas. The EOO is 10,902 km 2 and the AOO is 48 km 2 . Following the IUCN criteria, the preliminary assessment category is Vulnerable (VU). Representative
Distribution and habitat. Agrostis perennans sensu lato is distributed from Alaska to Patagonia, in Argentina and Chile, and also in the West Indies (Sylvester et al. 2020a). In the study zone, this species has been collected in Mexico City and the Mexican states of Chiapas, Chihuahua, Durango, Guanajuato, Guerrero, Hidalgo, Jalisco, México, Michoacán, Morelos, Oaxaca, Puebla, Querétaro, Tlaxcala, Veracruz, and Zacatecas; in the Guatemalan departments of Alta Verapaz, Baja Verapaz, Huehuetenango, Quetzaltenango, Quiché and San Marcos; in the Honduran state of Ocotepeque (Fig. 26A). It has also been reported from the Mexican states of Coahuila and San Luis Potosí Sánchez-Ken 2019), but no specimen from these states have been found. Records from the southern USA, in California, Arizona, New Mexico and Texas, appear to be misidentified specimens of A. scabra (Harvey 2007). This species grows in open areas of temperate forests, with conifers and Quercus, in cloud forests, stream edges, roadsides, and often in marshy places, between 622-3847 m a.s.l. (Fig. 27A).
Phenology. Specimens with spikelets have been collected year round, but most of them between the months of July and October (Fig. 28A).
Commentaries. Agrostis perennans is a widespread and variable species. It is considered a "dustbin" taxon (Sylvester et al. 2020a), which includes plants with basal and cauline leaves, usually flat leaf blades, more or less open panicles, usually unawned lemmas, and absent or minute paleas. More studies are necessary to clarify the relationships of the plants that have been included under this name, thus a wide circumscription of this species is adopted in this work.
Plants examined from the study zone fit well in A. perennans sensu lato, but at least three forms were observed: 1) fragile plants with open panicles; 2) more robust plants with open panicles; 3) robust plants with slightly contracted, denser panicles, and sometimes awned lemmas. The plants of the latter form have been called A. schaffneri, but despite the form of the panicles, no differences have been found in other characters, such as leaf anatomy and lemma micromorphology thus, this name is considered a synonym of A. perennans sensu lato.
Young plants of A. perennans sensu lato often have more conspicuous basal leaves and are confused with A. scabra, but differ from it in the leaf blades often greater than 2 mm wide, branches rebranching slightly above mid-length, and spikelets not clustered (vs. leaf blades up to 2(-3) mm wide, branches of the panicle usually rebranching in the upper third, with the spikelets usually clustered at the tips in A. scabra).
Agrostis perennans sensu lato is often confused with several species distributed in the study zone, which share several macromorphological, leaf blade anatomy, and lemma micromorphology characters. These species are A. bourgaei, A. calderoniae, A. ghiesbreghtii, A. hyemalis, A. laxissima, A. idahoensis, A. perennans, A. scabra, A. subrepens, and A. turrialbae. In the identification key provided in this work, a reasonably good separation of the mentioned species was reached using a combination of characters. Conservation status. Agrostis perenanns is a common and widespread species in the study zone. It is represented by 229 collections, with several populations occurring in 18 protected areas. The EOO is 992,915 km 2 and the AOO is 700 km 2 . Following the IUCN criteria, the preliminary assessment category is Least Concern (LC).
Anatomy and micromorphology. Leaf blades flat in transversal section; adaxial furrows medium-sized, wide; adaxial ribs rounded; keel absent; first order bundles circular to slightly elliptical in outline, sheath interrupted adaxially and abaxially, abaxial and adaxial sclerenchyma in girders, narrowing towards the bundle; second order bundles circular in outline, sheath interrupted abaxially, abaxial and adaxial sclerenchyma in strands; intercostal sclerenchyma absent; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells absent (Fig. 31A-C). Lemmas with transversal thickenings oblong, wider than the unthickened portions of the wall; prickle hairs abundant (Fig. 32A). Distribution and habitat. Agrostis scabra is native from Alaska to Guatemala. It has been introduced in Argentina and Chile (Rúgolo and Molina 1997), Venezuela, the West Indies and Europe (Dorr 2014). In the study zone, this species has been collected in the USA states of Arizona, California, New Mexico and Texas; in the Mexican states of Baja California, Baja California Sur, Chiapas, Chihuahua, Coahuila, Durango, Guanajuato, Jalisco, México, Michoacán, Morelos, Nuevo León, Oaxaca, Puebla, Querétaro, San Luis Potosí, Sinaloa, Sonora, Veracruz and Zacatecas; in the Guatemalan state of Huehuetenango (Fig. 26B). It has also been reported from Mexico City, and the Mexican states of Aguascalientes, Hidalgo, and Tlaxcala Sánchez-Ken 2019), but no specimens from these states were found. Agrostis scabra grows in open areas of temperate forests, with conifers and Quercus, also in cloud forests, alpine grasslands, stream edges and shrublands, between 630-3500 m a.s.l. (Fig. 27B).
Phenology. Specimens with spikelets have been collected year round, but most of them between the months of April and October (Fig. 28B).
Commentaries. The plants of this species are variable and at least two forms were observed in the study zone: 1) plants with very conspicuous basal leaves, with filiform and involute blades, distributed in Mexico and Guatemala; 2) plants with well-developed cauline leaves, with broader leaf blades, common in southern USA. Agrostis scabra is often confused with A. perennans, which share several leaf anatomy and lemma micromorphology characters (see the note under the description of that species). Agrostis scabra has been considered a synonym or a variety    Widén (1971: 77): L (L0059234 [image!])).
Anatomy and micromorphology. Leaf blades flat to convolute in transversal section; adaxial furrows medium-sized to deep, wide; adaxial ribs rounded; keel absent; first order bundles circular to slightly elliptical in outline, sheath interrupted adaxially and abaxially, abaxial and adaxial sclerenchyma in girders, narrowing towards the bundle; second order bundles circular in outline, sheath interrupted abaxially, abaxial and adaxial sclerenchyma in strands; intercostal sclerenchyma absent; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells absent (Fig. 31D, E). Lemmas without transversal thickenings, prickle hairs abundant to scarce (Fig. 32B).
Distribution and habitat. Introduced. Agrostis stolonifera is native to Eurasia and northern North America (Harvey 2007). In the study zone, this taxon has been collected from the Mexican states of Baja California and Veracruz (Fig. 26C). Agrostis has also been reported from the southern United States and Mexico City, also from the states of Chiapas, Chihuahua, Coahuila, Hidalgo, Jalisco, México, Michoacán, Nuevo León, Puebla, and Tlaxcala (Dávila et al. 2018;Sánchez-Ken 2019), but no specimens from these states have been seen. This taxon has been collected on stream edges and open areas of pine forests, between 1800-2100 m a.s.l. (Fig. 27C). There are more records of this species in the study zone, on databases (GBIF 2023d), but not all of them have images, and thus we were unable to confirm their identity.
Phenology. Specimens with spikelets have been collected from June to August (Fig. 28C).
Commentaries. Agrostis stolonifera is often confused with A. gigantea (see the note under the description of that species). This is a variable species and several infraspecific taxa have been recognized (e.g., Pohl and Davidse 1994;Rúgolo and Molina 1997). The plants from the study zone fit well in A. stolonifera var. palustris, which is distinguished from the typical variety in the more contracted panicles, up to 3 cm wide, and smaller spikelets of 1.6-2 mm long (vs. more open panicles, up to 6 cm wide, spikelets 2-2.5 mm long in the typical variety). The width of the panicles could be related to the age of the panicles, since they become contracted after anthesis, and thus varieties are not recognized here.
This taxon is also confused with Polypogon viridis (Gouan) Breistr., from which it is distinguished in the spikelets disarticulating above the glumes (vs. disarticulation below the glumes, with a pedicel fragment in P. viridis).

Agrostis subpatens
Anatomy and micromorphology. Leaf blades convolute to v-shaped in transversal section; adaxial furrows deep, narrow; adaxial ribs rounded to triangular; keel absent; first order bundles circular in outline, sheath not interrupted, abaxial and adaxial sclerenchyma in strands; second order bundles circular in outline, sheath not interrupted, abaxial and adaxial sclerenchyma in strands; intercostal sclerenchyma present, abaxial; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells absent (Fig. 31F, G). Lemmas with transversal thickenings irregular to oblong, wider than the unthickened portion of the wall; prickle hairs abundant (Fig. 32C).
Distribution and habitat. Agrostis subpatens is distributed from Chiapas, Mexico to Costa Rica (Pohl and Davidse 1994). It has also been reported from Venezuela (Luteyn 1999). In the study zone, it has been collected in the Mexican state of Chiapas and in the Guatemalan departments of Chimaltenango and Huehuetenango (Fig. 26D). This species has also been reported from Mexico City and the Mexican states of Hidalgo, Jalisco, México, Michoacán, Oaxaca, Puebla, Querétaro, Tlaxcala and Veracruz (Villaseñor 2016;Dávila et al. 2018; Sánchez-Ken 2019; Vigosa-Mercado and Ruiz-Sánchez, 2020), but these records correspond to misidentified specimens of A. tolucensis and A. turrialbae.

Agrostis subpatens grows in open areas of temperate forests with Pinus and
Juniperus, and in alpine grasslands, between 2900-3790 m a.s.l. (Fig. 27D).
Phenology. Specimens with spikelets have been collected in January, August and September (Fig. 28D).
Commentaries. This species is similar to A. tolucensis and A. turrialbae, with which it shares the basal filiform leaves, as well as several leaf blade anatomy and lemma micromorphology characters. Agrostis subpatens differs from A. tolucensis in the less dense and often more open panicles, with pedicels usually longer than the spikelets (vs. usually dense and spiciform panicles, pedicels usually shorter than the spikelets in A. tolucensis). It differs from A. turrialbae in the awned lemmas and absent palea (vs. unawned lemmas, palea up to 0.2 mm long in A. turrialbae).
Conservation status. Agrostis subpatens is known in the study zone from a few localities in southern Mexico and Guatemala. It is represented by seven collections, with several populations occurring in two protected areas. The EOO is 5,589 km 2 and the AOO is 20 km 2 . Following the IUCN criteria, the preliminary assessment category is Endangered (EN Anatomy and micromorphology. Leaf blades flat in transversal section; adaxial furrows deep, narrow; adaxial ribs square to triangular; keel absent; first order bundles circular in outline, sheath not interrupted, abaxial and adaxial sclerenchyma in strands; second order bundles circular in outline, sheath not interrupted, abaxial and adaxial sclerenchyma in strands; intercostal sclerenchyma absent; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells absent (Fig. 31H, I). Lemmas with transversal thickenings irregular, wider than the unthickened portion of the wall; prickle hairs abundant (Fig. 32D).
Distribution and habitat. Agrostis subrepens was described from the Sierra Madre Occidental, in Chihuahua, Mexico (Fig. 26E). It has also been reported from South America, in Bolivia, Ecuador, Colombia, Paraguay, Perú and Venezuela (Soreng and Peterson 2003;Idárraga-Piedrahita et al. 2011), but the specimens from these countries were not seen, and could represent misidentifications of other species. In the study zone, A. subrepens grows in wet areas, in forests with Pinus and Quercus, between 2000-2168 m in elevation (Fig. 27E).
Phenology. Specimens with spikelets have been collected from August to September (Fig. 28E).
Commentaries. The status of A. subrepens as a distinct species and its distribution has been put in doubt recently (Sylvester et al. 2020a). This species is very similar to A. perennans sensu lato and other awnless species of the study zone, but differs from them in the presence of pseudostolons, leaf blades with square to triangular adaxial ribs, and lemmas with irregular thickenings (vs. caespitose plants, leaf blades with rounded adaxial ribs, lemmas with usually polygonal thickenings). Some individuals of A. perennans sensu lato sometimes develop pseudostolons, but despite the leaf anatomy, there are few differences between the two taxa. We recognise A. subrepens as a distinct species, until more evidence is available.
It could also be confused with A. pallens from California and Baja California, but it is distinguished in the more open panicles, and unawned lemmas (vs. panicles often contracted, often awned lemmas), as well as the leaf anatomy.

Leaf anatomy.
Leaf blades involute to v-shaped in transversal section; adaxial furrows deep, narrow; adaxial ribs rounded to triangular; keel absent; first order bundles circular in outline, sheath not interrupted, abaxial and adaxial sclerenchyma in strands; second order bundles circular in outline, sheath not interrupted, abaxial and adaxial sclerenchyma; intercostal sclerenchyma present, abaxial; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells absent (Fig. 37A, B). Lemmas with transversal thickenings irregular to oblong, wider than the unthickened portion of the wall; prickle hairs abundant (32E).
Distribution and habitat. Agrostis tolucensis is distributed from northern Mexico to Chile. In the study zone, it has been collected in Mexico City, and the Mexican states of Chiapas, Durango, Guerrero, Hidalgo, Jalisco, México, Michoacán, Morelos, Oaxaca, Puebla, Tlaxcala, and Veracruz; in the Guatemalan departments of Sacatepéquez and San Marcos (Fig. 26F). It has also been reported from the Mexican states of Colima, Guanajuato, and San Luis Potosí (Villaseñor 2016;Sánchez-Ken 2019), but no specimens from these states were found. Agrostis tolucensis grows in open areas of temperate forests with Abies, Pinus, and Quercus, and alpine grasslands, between 1330-4520 m a.s.l. (Fig. 27F).
Phenology. Specimens with spikelets have been collected year round, but most of them between the months of July and November (Fig. 28F).
Commentaries. It has been reported that South American populations of this species develop long rhizomes (e.g. Renvoize 1998). This species is often confused with A. exarata and A. subpatens (see the notes under the description of these species). Agrostis tolucensis is a variable species, and several infraspecific taxa have been described, none of which are recognized in this work. In the study zone, at least three forms have been observed, but there is a continuous interval of variation in the populations of this species: 1) small plants with narrow leaf blades and panicles shortly exceeding the foliage, 2) larger plants with narrow leaf blades and panicles long-exserted from the foliage, 3) larger plants with broader leaf blades, more open panicles, and lemmas with awn inserted above mid-length of the lemma. The plants of the latter form have been called A. virescens, but they fit well in the continuous interval of variation of the populations. This species is also confused with A. meyenii Trin. (see the note under excluded species).
Anatomy and micromorphology. Leaf blades v-shaped to involute in transversal section; adaxial furrows deep, narrow; adaxial ribs rounded to triangular; keel absent; first order bundles circular in outline, sheath interrupted abaxially, abaxial and adaxial sclerenchyma in strands; second order bundles circular in outline, sheath interrupted abaxially, abaxial and adaxial sclerenchyma in strands; intercostal sclerenchyma present, abaxial; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells absent (Fig. 37C, D). Lemmas with transversal thickenings irregular to oblong, wider than the unthickened portion of the wall; prickle hairs present, abundant (Fig. 32F).
Distribution and habitat. Agrostis turrialbae is distributed from central Mexico to Costa Rica. It has also been reported from Colombia and Venezuela (Luteyn 1999;Soreng and Peterson 2003). In the study zone, this species has been collected in the Mexican states of Chiapas, México, Querétaro, Tlaxcala, and Veracruz, and the Guatemalan departments of Huehuetenango and San Marcos (Fig. 39A). It has also been reported from Hidalgo (Sánchez-Ken 2019), but no specimens from this state were seen. Agrostis turrialbae grows in open areas of temperate forests, with Pinus and Quercus, and alpine grasslands, between 1600-4240 m a.s.l. (Fig. 27G).
Phenology. Specimens with spikelets have been collected from June to February (Fig. 28G).
Commentaries. Populations of this species from central Mexico have been confused with A. subpatens by some authors (e.g., Acosta 2001; Vigosa-Mercado and Ruiz-Sánchez 2020) (see the note under the description of that species).  Agrostis turrialbae is similar to A. perennans sensu lato, and its identity has been put in doubt recently by Sylvester et al. (2020a). Both species share open panicles and unawned lemmas, as well as several lemma micromorphology characters. In the study zone, it has been found that the plants identified as A. turrialbae are consistently different from A. perennans, and are characterized by the small size of the plants, mostly basal leaves, leaf blades narrow and conduplicated to involute, with adaxial ribs rounded to triangular, with abaxial intercostal sclerenchyma, and purplish spikelets (vs. usually larger plants, usually basal and cauline leaves, but the basal ones often drying at anthesis, leaf blades wider and flat, with rounded adaxial ribs, without intercostal sclerenchyma, greenish to purplish spikelets in A. perennans). This species is scarcely different from A. idahoensis, from the southern USA (see the note under the description of that species).
Conservation status. Agrostis turrialbae is a widespread species in the study zone. It is represented by 30 collections, with several populations occurring in six protected areas. The EOO is 183,426 km 2 and the AOO is 84 km 2 . Following the IUCN criteria, the preliminary assessment category is Least Concern (LC).
Representative specimens examined.
Anatomy. Leaf blades convolute to v-shaped in transversal section; adaxial furrows medium-sized to deep, narrow; adaxial ribs rounded to triangular: keel absent; first order bundles circular in outline, sheath interrupted abaxially, abaxial sclerenchyma in strands or girders, narrowing towards the bundle, adaxial sclerenchyma in strands; second order bundles circular in outline, sheath interrupted abaxially, abaxial and adaxial sclerenchyma in strands; intercostal sclerenchyma absent; leaf margins with well-developed sclerenchyma caps, rounded; colorless cells absent (Fig. 37E, F). Lemmas with transversal thickenings irregular to oblong, wider than the unthickened portion of the wall; prickle hairs present, scarce (32G). This species has recently been transferred to the genus Podagrostis, under the name P. rosei (Swallen) Sylvester & Soreng (Sylvester et al. 2020b). It is endemic to Mexico, known from the states of Durango and Zacatecas (Vigosa-Mercado, 2022b). See the note under A. exserta for the differences between Agrostis and Podagrostis species. This name is a synonym of Polypogon viridis (Gouan) Breistr., which differs from Agrostis species in the spikelets disarticulating below the glumes, with a fragment of the pedicel (vs. disarticulation above the glumes).

Agrostis tandilensis (Kuntze) Parodi., Darwiniana 6: 158. 1943.
This species is native to South America, introduced to USA, where it is known to occur in vernal pools in coastal zones of Monterrey, San Diego, and Solano Counties (Rúgolo 2007), outside the study zone. It has also has been reported from Baja California, Mexico (Beetle et al. 1983), but no herbarium specimens associated with this record have been found. Some authors have treated this and other South American species as part of the genus Bromidium. Agrostis tandilensis differs from other Agrostis species in the hairy lemmas, with lateral veins excurrent as two long teeth (vs. lemmas glabrous or with hairs only on the callus, veins not or shortly excurrent).