Two new species of Aa (Orchidaceae, Spiranthoideae) from Colombia

Two new species of the Andean genus Aa (Orchidaceae, Spiranthoideae) are described: Aa lozanoi Szlach. and S. Nowak, and Aa figueroi Szlach. and S. Nowak. They are restricted in distribution mainly to Cordillera Oriental in the department of Cundinamarca, however, A. lozanoi was also collected in Cordillera Central and A. figueroi in Sierra Nevada de Santa Marta, in northern part of Colombia. Each species is described and illustrated, detailed habitat and distribution data are provided. A distribution map of the new species is presented. A dichotomous key for determination of the Colombian species of Aa is provided. Brief discussion about the most important threats for plants in Andes is presented.


Introduction
The orchid genus Aa Rchb.f. contains approximately 25 species occurring in Andean regions in South America and disjunctive population in Costa Rican mountains (Wood 2003). Ortiz (1995) reported seven species of Aa in Colombia. Our studies on Colombian orchids extend this number to ten, including two new species described in this paper. New species were discovered during researches conducted by the first author in Colombian National Herbarium in Bogota, COL [herbarium acronym followed Holmgren and Holmgren (1998)].
Aa, likes closely related genus Myrosmodes Rchb.f., is often found in the highest elevation of the Andes, i.e. above 3,100 m.a.s.l. (Wood 2003;Á lvarez-Molina and Cameron 2009;Trujillo and Vargas 2011). In result, they are commonly seen in vegetations, like open scrubs and woodlands, damp mountain meadows and paramo, dry puna, also in lower lomas formations from the desert coast of Peru (Wood 2003;Trujillo and Vargas 2011). Populations of some species in Argentina and Peru have been noted at lower elevations (Cocucci 1964;Trujillo and Rodriguez 2011).
Both Aa and Myrosmodes were distinguished from Altensteinia Kunth by Reichenbach (1854). However, in the later work, he classified all these genera under the name of Altensteinia (Reichenbach 1878). Aa was revalidated by Schlechter (1912Schlechter ( , 1920a, but later taxonomists still treated this genus as congeneric with Altensteinia. This situation reminded unchanged till Garay's (1978) treatment on Ecuadorian orchid flora. Since then Aa is widely accepted as distinct taxon. We recapitulate differences between genera in question in the Table 1. The genus is classify within Prescottinae (Dressler 1990(Dressler , 1993Szlachetko 1995), which in our opinion belongs to Spirantheae, what was suggested by Szlachetko (1995).
Representatives of Aa are terrestrial plants with inflorescence with many small, inconspicuous, greenish-white and non-resupinate flowers. Elongate peduncle is enclothed by hyaline, semi-transparent, imbricating sheaths. Dorsal sepal and petals are free form the gynostemium. Lip is globose and truncate, papillate or glabrous in the center, rounded or cordate at base, basally with a pair of globose calli. Lip margins are minutely denate to lacerate-fimbriate. Gynostemium is short, erect, rather massive. Anther is sessile or shortly stalked, erect motile with two parallel or basally slightly divergent chambers. Pollinia are two, but bipartite, powdery and oblong to ellipsoid-ovoid in shape. Staminodes are poorly developed, usually joined with the stigma and filament margins forming a dorsal, delicate clinandrium. Stigma is relatively large and flat. Rostellum is formed from apical part of the middle stigma lobe, and is restricted to the oval viscidium only, which is single, apical, detachable, cellular and multilayered ( Fig. 1; Szlachetko and Rutkowski 2000).
Flowers of all Aa species are small or even tiny, and diagnostic features hidden inside the flower cannot be traced without lenses. The proper identification of species requires careful examination of the lip and gynostemium morphology. It is necessary to pay special attention to the following characters; lip thickening and surface of its margins, form and presence of basal lip calli, as well as position of the anther (sessile vs stalked), form of the receptive surface and developing of the clinandrium. The most important discriminative characters well observed in cursory study concerns flower/floral bract ratio and position of the floral bracts in inflorescence.
The new species described here are restricted in distribution to the western part of Andes, mainly Cordillera Oriental in the department of Cundinamarca. Additionally, one specimen of Aa lozanoi was collected in Cordillera Central, department of Caldas (Fig. 2). Three specimens of A. figueroi were found on the isolated, pyramid-like prolongation of the Andes in North of Colombia, which are situated in protected area, Sierra Nevada de Santa Marta National Park. However, indigenous people' actions, like cattle grazing or agricultural development have severely altered the landscape (Davis et al. 1997;Luteyn 1999;Mittermeier et al. 2004). Cordillera Oriental in the department of Cundinamarca is an area where the most representatives of new species were collected.
In the following paper, we adopted key to determination of the species published by Garay (1978), but some discriminative features require to be commented. In his key, Garay (1978) stated that petals of Aa hartwegii Garay are crenulate, but in the original description he indicated the petals margins to be erose. Based on examination of 19 herbarium specimens from Colombia (e.g. Cleef 2265a, COL; Barclay 5282, COL; Pedraza 848, COL) and three from Ecuador (Korning and Thomsen 47294, AAU; Barclay and Juajibioy 9205, COL) including holotype (Hartweg s.n., K-L), we think that petals of A. hartwegii are crenulate.
According to Garay (1978), Aa nigrescens Schltr. is conspecific with A. leucantha (Rchb.f.) Schltr., but in our opinion they are separate species. Aa nigrescens is known only from the type specimen collected in Colombia (Madero s.n., B , AMES-lectotype) and A. leucantha from Ecuadorian (Lehmann 247, W-lectotype) and Colombian materials (Grubb, Curry and Fernandez Perez 752, COL; Cordoba, Lopez and Bernal 3210, COL; Diaz, Cleef, Rangel and Salamanca 2904, COL; Barclay and Juajibioy 6563, COL; Barkley and Araque 185159, COL). Based on studied materials, it seems that A. nigrescens is distinctive from A. leucantha by smaller leaves. In the former, they are 3 cm long and 1 cm wide, when in the latter 14 cm long and 2 cm wide. Tepals of A. nigrescens are almost linear to ligulate, versus mostly lanceolate in A. leucantha. Dorsal sepal of A. nigrescens is 3.5 mm long, 0.6-0.7 mm wide, petals 3.7 mm long, 0.3-0.4 mm wide and lateral sepals 4 mm long, 0.8 mm wide, when dorsal sepal of A. leucantha is 3 mm long, to 2 mm wide, petals to 3 mm long, 1 mm wide and lateral sepals to 4 mm long, 2.1 mm wide. Characteristic feature of A. nigrescens is glandular-pilose ovary, which is glabrous in A. leucantha. Additionally, black colour of flowers is well-seen on herbarium specimens of A. nigrescens, they are brownish in A. leucantha.

Taxonomic treatment
Aa lozanoi Szlach. and S. Nowak sp. nov. (Fig. 3). This species is similar to Aa argyrolepis Rchb.f., but margins of floral bracts, sepals and petals are entire, lip is very thick and fleshy, especially in the centre, lip margins are very minutely denticulate in the upper part, entire  (Szlachetko and Rutkowski 2000) below, stigma is transversely pandurate, clinandrium very obscure and anther shortly stalked.
Plants to 43 cm tall, erect, slender. Leaves absent at flowering. Scape slender, loosely 12-18 sheathed, terminated by 4-8 cm long, cylindrical many-flowered, dense, glabrous spike. Floral bracts to 13 mm long, somewhat surpassing the flowers, broadly ovate to ovate-lanceolate, acute, semi-transparent, margins entire. Sessile ovary to 4 mm long, glabrous or sparsely glandular. Margins of sepals and petals entire. Dorsal sepal up to 2.7 mm long and 1.5 mm wide, triangularovate to elliptic-ovate, obtuse to rounded at apex, 1-nerved. Petals up to 3 mm long and 1.2 mm wide, obliquely ligulate to oblong lanceolate, obtuse, 1-nerved. Lateral sepals to 3.5 mm long and 1.7 mm wide, obliquely oblong elliptic to ligulate, obtuse to rounded, 1-nerved. Lip to 3.2 mm long and 3 mm wide in natural position, globose, truncate at base, very thick and fleshy, especially in the centre, margins very minutely denticulate in the upper part, entire below, incurved, with a pair of globose calli. Gynostemium 1.2 mm long, erect, delicate, much swollen above the narrow base. Stigma transversely pandurate, very conspicuous. Clinandrium Notes: Aa lozanoi is easily separable from A. argyrolepis (Fig. 4) by its lip, petals and floral bracts. Despite A. argyrolepis, the floral bracts and petals margins are entire in the new species. The lip is very thick in the centre with margins being minutely denticulate in the upper part. According to Garay (1978), the lip of A. argyrolepis is ''fleshier than other segments'', but we found no differences in the thickness of the floral parts. The lip margin is lacerate-fimbriate in this species. The gynostemium morphology supplies additional characters distinguishing A. lozanoi from its closest congener. In the new species, gynostemium is much swollen towards the apex, hence obovoid, stigma is very large, transversely pandurate, clinandrium very obscure and anther shortly stalked. In contrast, the gynostemium of Aa argyrolepis is cylindrical, stigma is oblongelliptic, the clinandrium is prominent, more or less erose on margins and the anther sessile.
This species appears to be related to Aa colombiana Schltr., but the lip is almost orbicular when spread, very thick in the center and fimbriate along margins just above its base, clinandrium is shorter and spread between style and filament and anther is prominently stalked.
Type: Y. Figueroa C. 647-Colombia, Cundinamarca, Bogota, Localidad 5-Usme, sector del Embalse de Notes: Aa figueroi differs from A. colombiana (Fig. 6) in series of features concerning the lip and gynostemium morphology. Both species share similar lip form, but differ clearly in its margins. The lip of A. figueroi is fimbriate along margins, in contrast to A. colombiana where margins are lacerate-fimbriate. Garay (1978) stated that lip of A. colombiana is fleshier than other segments, but in A. figueroi it is exceptionally thick just below margins, having maximum in the centre. Gynostemium of the new species is 1.5 mm long (vs 1 mm in A. colombiana). Its clinandrium is prominent, spread between margins of style and filament reaching barely base of receptive surface, whereas in A. colombiana is spread between stigma and filament much exceeding half length of stigma. Both species are easily separable based on anther-it is stalked and subquadrate in A. figueroi, and sessile, reniform-cordate in A. colombiana. Additionally, stigma of new entity is reniform (vs broadly reniform in A. argyrolepis) and viscidium is rounded (vs transversely elliptic).