Oaxaca with a surface of 93,757 km² represents almost 5% of the Mexican territory and is the state that holds the highest biological diversity. The most well-known plant groups that are well represented in Mexico reach their highest diversity at national level (^{García-Mendoza, 2004}). One of these groups is the orchid family, which, according to ^{Salazar (2012)}, includes 721 species in Oaxaca, 6 of them being infraspecific taxa. Recently, 8 additional Orchidaceae species have been discovered or reported for Oaxaca State: Epidendrum melistagoides Hágsater et L. Sánchez (^{Hágsater & Sánchez, 2008}); Habenaria pinzonii R. González et Cuev.-Fig., H. rosulifolia Espejo et López-Ferr., and H. tetranema Schltr. (^{Pichardo, 2011}); Epidendrum eduardo-perezii Hágsater et E. Santiago (^{Hágsater & Santiago, 2013}); Acianthera pollardiana Solano (^{Solano, 2015}); as well Habenaria greenwoodiana R. González and H. tuerckheimii Schltr. (^{Mejía-Marín, Espejo-Serna, López-Ferrari, & Fonseca-Juárez, 2016}). With these, the orchid richness for Oaxaca rises to 729 taxa.

Orchidaceae from Oaxaca have been a well-studied group (^{Hágsater, Salazar, & Soto, 1998}; ^{Martínez, 2010}; ^{Pichardo, 2011}; ^{Salazar, 2012}; ^{Solano, Alonso, Rosado, Aguilar, & García, 2008}; ^{Solano, Bello, & Vásquez, 2007}; ^{Solano, Rubio, Lagunez, & Herrera, 2013}; ^{Soto & Salazar, 2004}); at national level, the orchid richness present in this state is, together with that from Chiapas, the highest in Mexico. On the other hand, the Oaxacan orchid richness is comparable to that reported for some Central American countries with similar or slightly larger surface, such as Guatemala (108,889 km², 817 species), Nicaragua (130,680 km², 679 species), and Honduras (112,090 km², 621 species) (^{Ossenbach, Pupulin, & Dressler, 2007}). Nonetheless, the orchid inventory of Oaxaca continues to increase as a result of an on-going floristic study, which has been intensified in recent years, both in areas not previously explored and those already studied by botanists. As a result of this floristic work, we have documented here 4 additional orchid species previously unknown for the State. With these additions, the orchid richness for Oaxaca is now increased to 733 species.

Barkeria skinneri (Bateman ex Lindl.) A. Rich. et Galeotti, Compt. Rend. Hebd. Séances Acad. Sci. 18: 506. 1844

Synonyms: Epidendrum skinneri Bateman et Lindl.; Dothilophis purpurea Raf., superfluous, based on Epidendrum skinneri; Barkeria skinneri (Bateman ex Lindl.) Paxton, superfluous; Barkeria skinneri var. major Paxton; Epidendrum fuchsii Regel; Epidendrum skinneri var. superbum R. Warner.

Examined specimen: Mexico. Oaxaca: municipio San Miguel Chimalapa, Congregación 05 de Noviembre (La Cristalina), paraje La Palmita, collected 8 Dec. 2010, pressed 19 Nov. 2014, Martinez s.n. (OAX!).

Distribution and habitat: Mexico and Guatemala. In Mexico it was previously known from the Central Plateau and the Sierra Madre of Chiapas (^{Cabrera, 2006}; ^{Soto, 2003}). In Oaxaca the species was discovered at the Sierra Atravesada (Fig. 1), where it grows as an epiphyte in the evergreen seasonal forest, at almost 1,000 m asl, and coexists with other orchids such as Epidendrum chlorops Rchb. f., Guarianthe aurantiaca (Bateman) Dressler et W.E. Higgins, Lycaste sp., Maxillaria variabilis Bateman ex Lindl., Nidema boothii Schltr, Notylia barkeri Lindl., Oncidium lindleyi (Galeotti ex Lindl.) R. Jiménez et Soto Arenas, Polystachya cerea Lindl., Prosthechea cochleata (L.) W. E. Higgins, Scaphyglottis fasciculata Hook., Stanhopea saccata Bateman, Stelis sp., and Trichocentrum cosymbephorum (C. Morren) R. Jiménez et Carnevali. Flowering is from October to December.

Figure 1 Map of Oaxaca showing the localities for the new orchid records: Barkeria skinneri (circle), Chysis limminghei (triangle), Habenaria macvaughiana (rhomb), and Lepanthes vivipara (star). 

Remarks: Barkeria skinneri is distinguished among other congeneric species by its long raceme, with star-like, magenta flowers (Fig. 2). A similar species is B. strophinx (Rchb. f.) Halb., especially in the form of floral parts, but it differs in its paniculate inflorescence (vs. racemose), pink-lilac flowers (vs. magenta), and callus on the lip formed by 2 prominent keels (vs. callus with 3-5 keels). In Mexico, B. skinneri is considered as a species subject to special protection (^{Semarnat, 2010}) because its populations are facing habitat loss and extraction for illicit trade (^{Cabrera, 2006}; ^{Soto, 2003}).

Figures 2-5 2: Barkeria skinneri; 3: Chysis limminghei; 4: Habenaria macvaughiana; 5: Lepanthes vivipara (photograph 2 by E. Martínez; 3 by A. Martínez; 4 and 5 by R. Solano). 

Chysis limminghei [as limminghii] Linden ex Rchb. f., in C. Koch, Berliner Allg. Gartenzeitung 26: 380. 1858

Synonyms: Chysis aurea Lindl. var. limminghei (Linden et Rchb. f.) Lem.; Chysis aurea Lindl. var. limminghei (Linden et Rchb. f.) Hook., superfluous; Chysis aurea Lindl. fo. limminghei (Linden et Rchb. f.) P.H. Allen.

Examined specimens: Mexico. Oaxaca: municipio Ciudad Ixtepec, Cerro Naranjo, 5 km to N of Nizanda, collected 8 Dec. 2003, pressed Jun. 2004, Pérez and Sierra (MEXU!); municipio Santa Maria Petlapa, Cerro Timbón, Cieneguilla, Juárez and Martínez (OAX in spirit!).

Distribution and habitat: Mexico and Guatemala. This is one of the few endemics species, restricted to lowland tropical rain forests from southeastern Mexico and adjacent portions of Guatemala (^{Chiron & Archila, 2010}; ^{Soto & Solano, 2007}). In Oaxaca the species was discovered in the Isthmus of Tehuantepec (Fig. 1), where it grows as an epiphyte in tropical rain or semi-evergreen forest, from 350 to 650 m asl. Flowering is in March.

Remarks: the original description of Chysis limminghii was published in ^{Koch (1858}: 380); however, both Missouri Botanical Garden (Tropicos: http://www.tropicos.org, recovered May 27, 2016) as International Plant Names Index (IPNI: http://www.ipn.org, recovered May 27, 2016) databases presented errors in the page assigned to its reference: page 308 in Tropicos, and page 880 in IPNI. The original citation for C. limminghei is corrected here.

Chysis limminghei is member of the C. aurea complex, which is characterized by the 5-7 subequal and puberulent keels at the base of the lip. Chysis violacea Dressler is a similar species, but it differs in its thicker pseudobulbs, more floriferous racemes, and larger flowers with darker spots on sepals and petals; it is also restricted to southern Central America. Another similar species is C. bruennowiana Rchb. f. et Warsz., from Nicaragua to Peru, but it differs in its longer and narrower pseudobulbs and different shape of the sepals and petals. Specimens from Oaxaca are different from the typical form of C. limminghei in their sepals and petals with yellow background, orange-ochre in the apical half with a magenta subapical spot (Fig. 3). In Mexico the species is considered as threatened (^{Semarnat, 2010}) due to its restricted distribution, low population densities, high habitat specificity, and extraction for illicit trade (^{Soto & Solano, 2007}).

Habenaria macvaughiana R. González, Bol. Inst. Bot. (Guadalajara) 3: 64. 1995[1997]

Examined specimen: Mexico. Oaxaca: municipio San Pedro y San Pablo Teposcolula, cerro La Campana, 26 Aug. 2010, Solano 3024 et al. (OAX!).

Distribution and habitat: Endemic to Mexico. The species was previously known from Jalisco (where the species was originally discovered) and Mexico State (^{González-Tamayo & Hernández-Hernández, 2010}; ^{Szeszko-Fabila, 2011}), and most likely also occurs in Michoacán. In Oaxaca the species was discovered at the high Mixtec region (Fig. 1), where it grows as a terrestrial in patches of thorny scrubland with Agave nuusaviorum García-Mend., Opuntia sp., Mammilaria sp., and Villadia sp., surrounded by pine-oak-juniper forest at 1,441 m asl. Flowering is from August to September.

Remarks: Habenaria macvaughiana (Fig. 4) is similar to H. diffusa A. Rich. et Galeotti, but it differs in its longer ovary (21-23 mm vs. ca. 14 mm), sepals obliquely ovate (vs. obliquely lanceolate), posterior lobe of the petals obliquely deltoid (vs. falcate), broader (1-1.7 vs. 1 mm wide) and rounded (vs. acuminate) mid lobe of the lip, and in its more or less cylindrical nectary that is more than twice as long as the midlobe of the lip (vs. clavate-fusiform and slightly longer than the midlobe of the lip). In the original description, H. macvaughiana was compared to H. crassicornis Lindl.; however, it is different in their petals and lip, which are pubescent with narrower lobes, and the nectary is shorter than the midlobe of the lip.

Lepanthes vivipara Salazar et Soto Arenas, Orquidea (Mexico City) 14: 207. 1996

Examined specimens: Mexico. Oaxaca: municipio Totontepec Villa de Morelos, Santa María Huitepec, 23 Mar. 2013, Gutiérrez s.n. (OAX, in spirit!); muncipio Totontepec Villa de Morelos, same locality, 28 Aug. 2015, Solano 4235, 4236, 4243 (OAX!).

Distribution and habitat: Endemic to Mexico. This species was previously only known from one locality in the Sierra Madre of Chiapas. In Oaxaca, this orchid was discovered in the Mixe region, at the southeastern extreme of the Sierra Madre Oriental (Fig. 1), where it grows as an epiphyte on small to medium tree trunks, in shaded, humid, ventilated sites within the cloud forest with pine and oak at 2,412 m asl. Flowering is from March to August.

Remarks: Lepanthes vivipara exhibits a floral morphology similar to some species of the L. stenophylla complex (^{Salazar & Soto, 1996}), but the former differs from the latter in their stems, which produce adventitious plantlets in the zone where the inflorescence normally emerges, the apex stem, and, on the other hand, their petals are proportionally large in relation to the length of sepals (Fig. 5). The locality where L. vivipara was discovered in Oaxaca holds the highest richness for Mexican Lepanthes; here, it coexists with a dozen congeners: L. aprica Catling et V.R. Catling, L. attenuata Salazar, Soto Arenas et O. Suárez, L. calopetala Salazar et Soto Arenas, L. catlingii Salazar et Soto Arenas, L. gabriellae Salazar et Soto Arenas, L. machorroi Salazar et Soto Arenas, L. mariae Salazar et Soto Arenas, L. mixe Salazar et Soto Arenas, L. oreophila Catling et V.R. Catling, L. papilionacea Salazar, Soto Arenas et O. Suárez, L. rekoi R.E. Schult., and L. thurstoniorum Salazar, Soto Arenas et O. Suárez.

We thank to Gabriela Cruz-García, who created the map presented here. The comments and suggestions of two anonymous reviewers were useful to improve the quality of the manuscript.