Materials and methods

In August 2014 and September 2015, the authors collected about 165 moss specimens, mainly in north- and southwestern localities in Aguascalientes (Table 1, Figure 1). Abandoned fields (San Antonio Montoya), riparian vegetation or stream beads (Ojo de Agua, Charco Azul), and scrubland vegetation elsewhere were the source of our collections. In addition, 140 miscellaneous specimens from the herbarium of Universidad Autónoma de Aguascalientes (HUAA), served to update the floristic list for that state. All specimens were identified and deposited in the Bryophyte Collection of the National Herbarium (MEXU), with duplicates for HUAA and other herbaria.

Figure 1 Collecting localities in Aguascalientes. Localities reported by ^{Delgadillo et al. (2015)} are indicated by diamonds. Solid circles represent recent collections by the authors and by HUAA personnel. 

Results

The list of taxa in Table 2 contains 50 new records for the moss flora of Aguascalientes. These are unmarked under “A” to distinguish them from previously reported records (^{Delgadillo et al. 2015}), and bring the total number to 95 taxa, i.e., four species above the previously estimated number. Most of the species are also known from Jalisco or Zacatecas so that the Aguascalientes moss flora may indeed represent an extension of the flora from those states (^{Delgadillo et al. 2015}).

The moss flora of Aguascalientes contains numerous taxa from dry land areas. Among them, the Pottiaceae are rather frequent, with 34 species and varieties for a 36 % of the total state moss flora. The Bryaceae, with 11 species, only make a 12 %. The Grimmiaceae, with seven species (ca. 7 % of the total), are also noteworthy because they are rock inhabitants and more diverse than fifteen other families that are represented by five or less in the state moss flora. At the generic level mosses are represented by 43 genera, or nearly 13 % of the Mexican moss flora.

The list contains such taxa as Anomobryum conicum that seem rare or may be infrequently collected while others such as Aloina hamulus and Didymodon spp., are rather frequent in the region. The flora also includes a significant number of high elevation taxa that are known to occur in Jalisco or in the alpine regions of central Mexico; Aongstroemia orientalis and species of Grimmia are in this group. Most species live on soil or rocks. The number of epiphytes is comparatively small (14 species, Table 2) because, in addition to low rainfall, tree cover is sparse and may offer scarce protection against desiccation. Species of Fabronia, Leskea, Lindbergia, and Orthotrichum usually occupy these habitats.

Hennediella stanfordensis, only known from the state of Guerrero, is represented by two poorly preserved specimens from San Francisco de los Romo area, but the identification is facilitated by a differentiated papillose leaf margin with thick-walled elongated cells, and a mucro standing against an entire leaf apex. Jaffueliobryum arsenei and Ptychomitrium chimborazense have narrow ranges; the former is known from Zacatecas to Querétaro, but in Aguascalientes it seems more frequent although it is officially recognized as rare (^{Delgadillo 1996}). The distribution of the latter in Mexico extends from Zacatecas to Puebla, but collections have been occasional, only. Archidium donnellii, Pleuridium mexicanum, and Tortula acaulon are the only cleistocarpic mosses known for this state. Anomobryum plicatum and Entosthodon obtusatus are tentatively included in the list because specimen identification was uncertain due to immature or sterile material available. There are no species restricted to Aguascalientes, but its flora includes Grimmia involucrata, G. pulla, Hennediella heteroloma, Jaffueliobryum arsenei, and Trichostomum subangustifolium, endemic to Mexico.

Although most species are cited in ^{Sharp et al. (1994)}, the keys introduced in this contribution reflect recent taxonomic and nomenclatural arrangements. They should facilitate the identification of mosses from Aguascalientes. For this purpose, observations in the following paragraph are to be considered.

Moss keys usually distinguish the erect from the prostrate habit. Such growth forms may be labeled as “acrocarpous” and “pleurocarpous”, as defined in standard floras and glossaries, but they have been omitted in the keys to avoid confusion. Broadly speaking, such terms describe the position of the perichaetium in a branching system. In the acrocarpous mosses, a single perichaetium is formed at the end of a primary module of a branch system; in the pleurocarpous mosses one or more perichaetia are produced per primary or secondary module, at the end of lateral innovations that lack branch primordia or developed branches. A third moss growth type that is seldom mentioned is termed “cladocarpous” where the primary modules end in vegetative growth and the perichaetia are produced at the end of lateral branches of secondary or tertiary branches (^{La Farge-England 1996}). ^{Withey (1996)} suggests that the cladocarpous condition is a special form of pleurocarpy. In Aguascalientes, the species of Braunia may be considered as acrocarpous while Anoectangium aestivum is cladocarpous. However, because of their prostrate or erect condition, they have been termed pleurocarpous and acrocarpous, respectively, in standard taxonomic or floristic manuals.

Discussion

The Aguascalientes floristic list might contain a larger number of species for various reasons. There are many field sites that require exploration, but are privately owned and are not readily accessible. On the other hand, farmland, cattle ranches, and industrial facilities are common and represent heavily disturbed areas whose value in moss diversity studies is virtually nil. Frequent disturbance favors the arrival of tolerant species such as Bryum argenteum, B. chryseum or Funaria hygrometrica while many other species are displaced from their original substrates. Despite the need for additional exploration, because the predicted number of species is essentially the same as the number of taxa recovered in our sampling, we conclude that species richness for the state has been conveniently evaluated.

With a land surface area of about 5,471 km² (^{García de Miranda & Falcón de Gyves 1984}), Aguascalientes is one of the smallest states in Mexico. In spite its small size, its moss flora holds species or groups of species with peculiar features. There is a group of species that occupies disturbed areas whose frequency varies in response to human activities, as mentioned above. In this regard, the eastern and central portions of the state harbor cities, industry, highways, farm and cattle ranges that reduce or modify species dynamics depending on soil management practices. Group composition may vary with the geography, climate, and vegetation of the state; the northern areas are dominated by the dry land species while the western elevations incorporate highland taxa. Detailed mapping and phytosociological evaluations are required in this and neighboring states to detect associations. One such association may be represented by mosses growing on limestone or soils derived from calcareous rocks. Aloina hamulus, Didymodon revolutus, Globulinella globifera, and Pseudocrossidium replicatum are frequently found together in the same areas so that by finding one species the presence of others may be predicted. The frequency of sites where these species occur perhaps reflect the extent of human interference in natural moss communities.

The cleistocarpic species, represented by Archidium donnellii, Pleuridium mexicanum y Tortula acaulon, illustrate the structural and functional diversity of mosses in Aguascalientes. These species may be more frequent in disturbed sites because, in the absence of a dehiscent system, capsules may open by mechanical disturbance by cattle or agricultural equipment. The presence of such species as Jaffueliobryum arsenei marks the existence of other peculiar features in the area. For instance, the monoicous condition termed “cryptoicous” observed in J. arsenei is characterized by the position of both sex organs on the same stem. The perichaetial leaves enclose a small male branch growing from the vaginula, at the base of the sporophyte. The same condition has been described in Ptychomitrium (^{Deguchi 1977}, ^{Deguchi & Takeda 1986}) and Jaffueliobryum (^{Churchill 1987}); both genera are part of the Aguascalientes moss flora.

From the geographical point of view, diversity studies may benefit from the use of environmental indicators. The introductory contribution (^{Delgadillo et al. 2015}) indicated that the potential number of species in the flora would be about 91moss taxa. Because of the information in this contribution, this may be regarded as a well-known flora. Nevertheless, further exploration elsewhere may confirm or expand knowledge of the distribution of individual taxa and assist in the evaluation of the conservation status of rare or endangered species.

Key to the known moss species in Aguascalientes

Mosses with prostrate or lateral sporophytes

Mosses with erect stems and apical sporophytes