The genus Aa from the orchid family (Orchidaceae) comprises 26 species, all of which occur at high altitudes in the Andes. The small, perennial plants grow terrestrially.
All species of this genus form a basal rosette of spirally arranged leaves. The leaves are oblong - oval shaped to lanceolate, pointed ending, sometimes of thick, fleshy texture. The leaves can usually only made after the flowering period. The roots are thick and fleshy, sometimes hairy.
The racemose inflorescence appears at the side of the leafy shoot. The supporting Flower stem is covered with loose the stem comprehensive, differ -ended, translucent bracts, but not with leaves. Below he is hairless, but often glandular hairy at the top. The small flowers are sitting together at the end of the inflorescence axis. They are surrounded by papery bracts that are flowering in size usually excel and beaten back in the heyday. The ovary is not stalked, glabrous or glandular- hairy. The flowers appear 'upside. The petals are - in contrast to Altensteinia - little hairy. The sepals resemble each other, they are free or sometimes fused together at the base for a short distance. The petals are narrower in shape. The lip is hemispherical and fits like a cap over the flower at the base, it is provided with two callosities, the edge is fringed and folded inwards. The gynostemium is also hairless and very short. The Klinandrium (a tissue at the tip of gynostemium, over the anther ) is greatly reduced. The rostellum ( a separation between anther and stigma tissue ) is short and is transverse to the column axis. The stigma itself is large, broad and kidney-shaped. The pollen is organized in four soft pollinia, they are linear in shape. The flowers give off an unpleasant odor, which could be related to the attraction of flies as pollinators.
Most species are found in the high altitudes of the Andes in South America and Costa Rica above the timberline at altitudes of 3000 - 4400 meters. You get there before in the referred Páramo grasslands, in bogs, in bamboo thickets, bushes and sparse Weinmannia forests.
Systematics and Botanical History
First scientific descriptions of these orchids gave Karl Sigismund Kunth, the first Ophrys paleacea, later Altensteinia paleacea called a kind of 1815. Heinrich Gustav Reichenbach divided the genus Altensteinia in 1854 and described the genus Aa with two species, Aa and Aa paleacea argyrolepis. In the first description Reichenbach is no explanation for the unusual name Aa. There is a presumption that he had chosen the name to always show up in alphabetical lists in the first place. It could also be a tribute to Pieter van der Aa, the printer of Paul Hermann's Paradisus Batavus. A third possibility is that the name is derived as shortening of the closely related genus Altensteinia. A few years later Reichenbach made his division again reversed and turned again to all types Altensteinia, Rudolf Schlechter presented again in 1912 establishes the separation: now significantly more species were known, which made a renewed separation appear sensible.
Most species seem to mostly reproduce by self-pollination. Within individual populations, the plants look pretty why from uniform to neighboring populations of the same species, however, significant deviations can occur. Since the descriptions of species based only on very limited collections which do not include the whole range of variation of the taxonomic status and the delimitation of the species is uncertain.
The following species are known:
- Aa achalensis Schltr. , Central Argentina, San Luis, Córdoba
- Aa argyrolepis ( Rchb.f. ) Rchb.f., Colombia to Ecuador
- Aa aurantiaca D.Trujillo, Peru
- Aa calceata ( Rchb.f. ) Schltr. , Peru to Bolivia
- Aa colombiana Schltr. , Colombia to Ecuador
- Aa denticulata Schltr. , Colombia to Ecuador
- Aa erosa ( Rchb.f. ) Schltr. , Peru
- Aa fiebrigii ( Schltr. ) Schltr. , Bolivia to northwestern Argentina
- Aa hartwegii Garay, Northwest Venezuela to Ecuador
- Aa Hieronymi ( Cogn. ) Schltr. , Northwest Argentina to Cordoba
- Aa leucantha ( Rchb.f. ) Schltr. , Colombia to Ecuador
- Aa lorentzii Schltr. , Northwest Argentina
- Aa macra Schltr. , Ecuador
- Aa maderoi Schltr. , Venezuela to Ecuador
- Aa mandonii ( Rchb.f. ) Schltr. , Peru to Bolivia
- Aa matthewsii ( Rchb.f. ) Schltr. , Peru
- Aa microtidis Schltr. , Bolivia
- Aa nervosa ( Kraenzl. ) Schltr. Northern Chile
- Aa paleacea ( Kunth ) Rchb.f., Costa Rica to Bolivia
- Aa riobambae Schltr. , Ecuador
- Aa rosei Ames, Peru
- Aa schickendanzii Schltr. , Northwest Argentina
- Aa sphaeroglossa Schltr. , Bolivia
- Aa trilobulata Schltr. , Bolivia
- Aa weddeliana ( Rchb.f. ) Schltr. , Peru to northwestern Argentina