Materials and methods

Geographical data and richness analyses. Data were obtained from herbarium specimens in the following collections: CHAPA, CIIDIR, ENCB, FCME, FEZA, IBUG, IEB, and MEXU (acronyms according to ^{Thiers 2019}). We also examined the virtual herbaria of ARIZ, ASU, BH, F, GH, MICH, MO, NY, RSABG, US, and WIS; and searched for specimens in the Southwest Environmental Information Network (SEINet) from Symbiota content management system (^{Gries et al. 2014}). In addition, taxonomic treatments, monographs, and floristic studies were reviewed for distributional data (^{Matuda 1975}, ^{Verhoek-Williams 1975}, ^{Piña 1985 a}, ^b, ^c, ^{Piña 1986}, ^{McVaugh 1989}, ^{Ayala-Hernández 2006}, ^{Rodríguez & Castro-Castro 2007}, ^{Castillejos-Cruz 2009}, ^{Rodríguez 2009}, ^{García-Mendoza 2011}, ^{Castro-Castro et al. 2017}, ²⁰¹⁸). When doubtful taxonomic identity records were detected, digitalized voucher specimens were analyzed, or images were requested from the staff of the corresponding herbaria.

Occurrence data was cleaned by eliminating repeated records and ambiguous locations and then visualized using the program ArcView GIS ver. 10.3 (^{ESRI 2014}). The number of Manfreda species in Guerrero was quantified by municipality, vegetation type (^{Rzedowski 1990}), biogeographic province (^{Morrone et al. 2017}), and a standardized grid cell. The grid cell size was chosen according to the criteria of ^{Willis et al. (2003)}, with the modification of ^{Suárez-Mota & Villaseñor (2011)}. Based on this method, the maximum distance of each taxon was averaged, and the value was divided by the number of species with maximum distance values greater than zero, for which 13 species reached the value in our analysis. The quotient was used to define the length of the cell. The grid analysis was performed with DIVA-GIS 4.2 (^{Hijmans et al. 2004}). In this way, the state of Guerrero was divided into 162 cells of 144 km².

Taxonomic treatment. The morphological description and illustration of the new species are based on traditional taxonomic methods (^{Simpson 2006}). Descriptions and measurements were carried out under a Zeiss Stemi 305 stereomicroscope. The line illustration of the new species was prepared from herbarium specimens, alcohol-preserved material and digital photos. The terminology used follows ^{Verhoek-Williams (1975)}, ^{Castillejos-Cruz (2009)}, and ^{Castro-Castro et al. (2017}, ²⁰¹⁸⁾. The morphological data obtained from the revised herbaria specimens were summarized to produce the descriptions, which served to prepare the identification key and the diagnosis of the new species. The conservation status of the new species was determined based on field observations and applying the IUCN red list criteria (^{IUCN 2019}). We used GeoCAT program (^{Bachman et al. 2011}) to estimate the extent of occurrence (EOO) and area of occupancy (AOO) indices for evaluating the geographic range.

Results

Geographical data and richness analyses. Our database included 86 different records, with 114 specimens, for 14 species of Manfreda in Guerrero (Appendix 1). We corroborated the taxonomic identifications and georeferenced 52 % of all records that lacked geographic coordinates. Manfreda collections in Guerrero are limited to 33 of the 81 municipalities in the state. The records and richness by municipalities are concentrated in Chilpancingo de Los Bravo (18 records / 5 spp.), Taxco de Alarcón (8 records / 3 spp.), Chilapa de Álvarez (7 records / 4 spp.), and Leonardo Bravo (7 records / 3 spp.). On the other hand, in Arcelia, Chilapa de Álvarez, Colotlipa, Carrizal de Bravo, Guayameo, Leonardo Bravo, Taxco de Alarcón, Técpan de Galeana, Tzitzio, and Zirándaro are restricted five endemic species to Guerrero (M. arceliensis Art.Castro, J.G. Zavala & Cruz Durán, M. bulbulifera Castillejos & E. Solano, M. guerrerensis Matuda, M. justosierrana García-Mend., and M. parva Aaron Rodr.; Table 1).

Manfreda species in Guerrero have been collected mostly in temperate and cold conditions with coniferous, oak-pine, oak, and pine forest, where 13 species are located: M. arceliensis, M. bulbulifera, M. chamelensis E.J. Lott & Verh.-Will., M. guerrerensis, M. hauniensis (J.B. Peterson) Verh.-Will., M. aff. jaliscana Rose, M. justosierrana, M. maculata (C. Mart.) Rose, M. parva, M. pringlei Rose, M. pubescens (Regel & Ortgies) Verh.-Will. ex Piña, M. scabra (Ort.) McVaugh, and M. umbrophila García-Mend. Meanwhile, in warm climatic conditions with tropical deciduous forest, as in subdeciduous tropical forest, savannoid vegetation, and palmar, it is possible to locate: M. chamelensis, M. hauniensis, M. littoralis García-Mend., A. Castañeda & S. Franco, M. maculata, M. pubescens, and M. scabra (Table 1).

The elevation range in which Manfreda has been collected in Guerrero is wide, from 15-450 m in Acapulco, Ajuchitlán del Progreso, José Azueta, and Técpan de Galeana [M. chamelensis, M. littoralis and M. scabra]; to 1,900-2,628 m in Alpoyeca, Atilxtac, Atoyac de Alvarez, Carrizal de Bravo, Chichihualco, Chilapa de Álvarez, Eduardo Neri, Leonardo Bravo, Metlaltónoc, Taxco de Alarcón, and Técpan de Galeana [M. guerrerensis, M. hauniensis, M. justosierrana, M. pringlei, M. scabra, M. pubescens, and M. umbrophila].

According to ^{Morrone et al. (2017)} biogeographic provinces in Guerrero, Manfreda has been collected in the Sierra Madre del Sur (37 records / 10 spp.), Balsas Basin (26 records / 9 spp.), Transmexican Volcanic Belt (8 records / 4 spp.), and Pacific Lowlands (8 records / 3 spp.) (Figure 1).

In the grid analysis, 34 cells had at least one record, that is, ±7 % of the analyzed area. The number of species per cell varied from one to four, but just two cells contained four species. In the first of these cells inhabit Manfreda aff. jaliscana, M. justosierrana, M. maculata, and M. pringlei. While M. guerrerensis, M. justosierrana, M. pringlei, and M. pubescens were found in the second cell. In general, Manfreda richness is concentrated in 8 cells located in the municipalities Chilpancingo de los Bravo, Leonardo Bravo and Taxco de Alarcón, which are in the Balsas Basin, Sierra Madre del Sur, and Transmexican Volcanic Belt biographical provinces, and bring together nine species (Figure 1).

Discussion

As might be expected, the Manfreda species richness distribution patterns in Guerrero are similar to those patterns found in other angiosperm groups. For example, there is a geographical correspondence between Manfreda richness areas in Guerrero and the diversity and endemism patterns for another 507 species of Mesoamerican geophyte monocots (^{Sosa & Loera 2017}). Moreover, the same areas identified here are also associated with a high degree of richness, endemism and conservation priority for other plant groups; such as the perennial herbs species of Cosmos section Discopoda (DC.) Sherff (^{Vargas-Amado et al. 2013}, ²⁰¹⁹), bulbous herbaceous of Iridaceae tribe Tigridieae (^{Munguía-Lino et al. 2016}), 79 species of the genus Salvia L. (^{Martínez-Gordillo et al. 2016}) and the areas of endemism found for 32 taxa restricted to the Sierra Madre del Sur (^{Santiago-Alvarado et al. 2016}).

The greatest species richness of Manfreda in Mexico is found in Guerrero, wherein 14 species have been registered and five are endemic (^{Castro-Castro et al. 2017}, ²⁰¹⁸; Table 1). The relatively low number of collections for the genus, which have been carried out in a period of just less than 100 years (1926-2014), is striking. Manfreda collections in Guerrero are limited to 33 of the 81 municipalities in the state, 40.7 % of the political territory of the state. Given the high diversity of Manfreda in Guerrero, the elevated endemism and the low coverage of botanical explorations focus on this group in the state, current estimates of species diversity are likely under-estimates and new species are likely to be found. For example, although in Guerrero the greatest diversity of Manfreda has been found in temperate and cold environments, it is advisable to focus on the collection efforts towards the tropical areas of Pacific Lowlands, since according to ^{Castro-Castro et al. (2017}, ²⁰¹⁸⁾, in this province is where the genus Manfreda has its highest species richness in Mexico. A final recommendation in this regard, is the detailed review of the plants included as M. aff. jaliscana. The six specimens analyzed show a homogeneous morphology among them, but contrasting in the sizes of the leaves, flowers and filaments with respect to other specimens collected in western and northwestern Mexico, the area where the species was described (^{Rose 1903}), and it has been reported more frequently (^{Castro-Castro et al. 2017}). In addition, the phenology of the populations of Guerrero differs in what is known for M. jaliscana, which has been reported in bloom mostly during the dry period (see Appendix 1 and ^{Rodríguez & Castro-Castro 2007}).

During the present investigation it was possible to detect another set of specimens that could not be assigned to any of the known species in Manfreda. The plants were collected in the municipality of Arcelia, an area where only two specimens of the genus had been previously collected before 2006 (Appendix 1). Given the general morphology, these plants could be related to M. maculata and M. parva. However, there are multiple differences that allow them to be recognized as an undescribed species. These dissimilarities and similitudes are detailed in the following lines together with data on the ecological preferences, taxonomic notes of the new species and a key for the identification of Manfreda in Guerrero.

Taxonomic treatment. Manfreda arceliensis Art.Castro, J.G. Zavala & Cruz Durán sp. nov. (Figure 2).

Type: Mexico. Guerrero: Arcelia municipality, Filo del Cerro el Tepehuaje, Campo Morado, 1393 m, 19 July 2006 (fl), R. Cruz-Durán et al. 6428 (Holotype: FCME; Isotype: CIIDIR).

Diagnosis. Manfreda arceliensis is morphologically similar to M. maculata and M. parva, but it can be distinguished from the former by the herbaceous leaves, broadly oblanceolate, flat, and glabrous (vs. coriaceous, lanceolate to oblanceolate, slightly channeled, undulate, and densely pubescent on both faces), inflorescence 41-52 cm long with 2-4 flowers [vs. (30-) 60-120 cm long with 6-22 flowers], first sterile bracts 1.4-3.3 cm long (vs. 4.5-8.5 cm long), perigone funnel-shaped (vs. tubular), and filaments inserted 5-5.2 mm below the sinuses of the lobes (vs. 6-10 mm). For its part, it distinguishes from M. parva for developing a bulb ovoid, 3-3.8 × 2.3-2.7 cm (vs. oblong, 2-2.5 × 1-2 cm), leaves 2-3, broadly oblanceolate, flat, green with densely purple spots [vs. (5-)11-24, linear, channeled, green concolorous], inflorescence with 3-4 flowers [vs. (4-)9-15], peduncle 38-48 cm long with 3-4 bracts (vs. peduncle 19-26 cm long with 4-7 bracts), and the first sterile bracts linear, 1.4-3.3 × 0.12-0.25 cm (vs. lanceolate, 6-8 × 0.7-1 cm).

Perennial herb, 42-52 cm tall. Corm ovoid 3-3.8 × 2.3-2.7 cm, with small buds and thickened, contractile and fleshy roots. Roots filiform, 3.5-6.5 cm long. Bulb ovoid, 3-3.8 × 2.3-2.7 cm, tunicate, straw. Leaves 2-3 in a basal rosette, alternate, broadly oblanceolate, 10-14.5 × 1.9-4 cm, erect, flat, thin to leathery, green with densely purple spots, upper and lower surface tiny papillate, acute and soft apex, narrowed into a basal petiolar portion, margin hyaline, smooth. Inflorescence spiciform, 41-52 cm long, erect, arcuate apex, internodes decreasing in length towards the apex; peduncle 38-48 cm long, bracts 3-4, first sterile bracts linear, 14-33 × 1.2-2.5 mm, the closest to the rachis 6.6-7 × 0.4-0.7 mm, both acute, truncate, clasping, thin, brownish green, concolorous, upper and lower surface smooth, hyaline, adpressed to divaricate; rachis lax, 1-2.6(-4.5) cm long, with 2-4 floral nodes, internodes 1.2-3 cm long, primary floral bracts linear, 1.6-4.4 × 0.5-0.6 mm, acute, truncate, smooth, persistent, yellow-brow, erect or reflexed. Bracteoles 1 at each floral node, ensiform to acicular, 0.8-1.1 × 0.1-0.2 mm, entire, yellow-brow. Flowers actinomorphic, funnel-shaped, ascending, yellowish green and with dense and fine points of reddish purple on the outside and yellow pale inside in anthesis; perigone tube 1.5-1.8 cm long, 0.6-0.9 cm wide at the base of the lobes, tubular but widen slightly towards its distal portion, slightly curved; lobes 6.5-7.5 × 3.6-4.4 mm, ovate-deltate, markedly divergent to reflexed in anthesis, apices with a tuft of short white hairs. Stamens epitepalous, antitepalous, phanerantherous; filaments subulate, 1.7-1.9 cm long from their insertion into the perigone tube, inserted 5-5.2 mm below the sinuses of the lobes, yellow brown to reddish; anthers elliptic, 8-9 × 1.5-1.8 mm, yellow with dense and fine points of reddish purple. Ovary 7.5-9.7 × 3.2-4 mm, ovoid to narrowly ovoid; style filiform, 2.8-3 cm long in anthesis, purple, exserted from the perigone tube by 1.3-1.5 cm in anthesis; stigma trigonous, trilobed, papillose, clavate. Fruit unknown.

Distribution, ecology, and phenology. Manfreda arceliensis is endemic to northern Guerrero in the transition zone between Balsas Basin and Sierra Madre del Sur biogeographic provinces. It inhabits oak forest with savannoid vegetation elements; in areas with deep and acid soils at an elevation of 1,248-1,393 m. Manfreda arceliensis is associated with Byrsonima crassifolia (L.) Kunth, Cardiostigma longispatha (Herb.) Baker, Clethra hirsutovillosa S. Valencia & Cruz Durán, Dodonaea viscosa Jacq., Psidium sp. and Quercus magnoliifolia Née. The species flowers in July.

Conservation status. Manfreda arceliensis is represented by two collections in close proximity. The EOO was of 0.76 km², and the size of the AOO is 8 km², based on cells of 2 × 2 km. Adjusting to EOO and AOO areas results and following the ^{IUCN (2019)} criteria (extent of occurrence estimated to be less than 100 km² and known to exist at only a single location), a preliminary category of Critically Endangered is proposed (CR/B1a and B2a). It is advisable to perform additional explorations and collections in the area where the species is found.

Etymology. The name of the new species refers to the municipality of Arcelia, Guerrero, Mexico.

Additional specimens examined. Mexico. Guerrero: Arcelia municipality, cerca de la cañada El Limón, Campo Morado, 1,248 m, 17 July 2006 (fl), R. Cruz-Durán et al. 6287 (CIIDIR, FCME).

Relationship and taxonomic position. Manfreda arceliensis is the smallest species among all the taxa of the genus present in Guerrero. Moreover, it is the species that develops fewer flowers in Manfreda. Morphologically, M. arceliensis is similar to M. maculata and M. parva, the differences and similarities in morphological traits among these three species are highlighted in the diagnosis and the key for Manfreda in Guerrero provided below.

Key for Manfreda in Guerrero, Mexico