Pleurothallis

Pleurothallis, abbreviated Pths in horticultural trade, is a genus of orchids commonly named Bonnet Orchids. The genus name is derived from the Greek word 'pleurothallos', meaning 'riblike branches'. This refers to the rib-like stems of many species.
This was a huge genus, which used to contain more than 1,200 species - the second largest in the Orchidaceae after Bulbophyllum. In 2004, it decreased by more than half when many species were moved into new genera (Monogr. Syst. Bot. Missouri Bot. Gard. 95: 256. Feb 2004).

Taxonomy

To bring some order in this extremely diverse genus, 29 subgenera and 25 sections had been created. Much of this work has been done by Dr. C. Luer of MOBOT. A new analysis, based on DNA testing, has confirmed on the whole the classification of the subtribe Pleurothallidinae, with however Pleurothallis as the main difference. This should not surprise anyone, since this somewhat artificial genus has been the dumping ground for species that did not fit into any other genus. New genetic insight has broken up this huge genus and made it more consistent with the principles of monophyletic genera and evolutionary relationships.
Several times before, a splitting up has been attempted, but there were always too many intermediate forms. In 2004 the new genera Acianthera, Ancipitia, Antilla, Apoda-prorepentia, Areldia, Atopoglossum, Brenesia, Crocodeilanthe were created, incorporating a large number of former Pleurothallis species (Monogr. Syst. Bot. Missouri Bot. Gard. 95: 255. 2004 [Feb 2004]). The subgenera Pleurothallis and Specklinia are becoming separate genera, and the subgenus Acuminatae might become the proposed genus Anathallis.
Other allied genera include: Dracula, Masdevallia, Restrepia and Stelis. ^[1]

Synonymy

The following taxa: Acronia C.Presl, Andreettaea Luer, Centranthera Scheidw., Colombiana Ospina, Cryptophoranthus Barb.Rodr., Geocalpa Brieger (nom. inval.), Kraenzlinella Kuntze, Otopetalum Lehm. & Kraenzl., Pabstiella Brieger & Senghas, Palmoglossum Klotzsch ex Rchb.f., Phloeophila Hoehne & Schltr., Physosiphon Lindl., Physothallis Garay, Pleurobotryum Barb.Rodr., Pseudoctomeria Kraenzl., Pseudostelis Schltr., Rhynchopera Klotzsch, Sarracenella Luer, Specklinia Lindl. and Talpinaria H.Karst. are synonyms of Pleurothallis.