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).
It is a completely New World group and occurs from the southeast United States down into the tropics of South America, with most species in the high Andes chain of cloud forest in Colombia. They grow in dry or wet, tropical or temperate climates.
As a group they show a huge range in vegetative form, terrestrial or epiphytic, and can be found as tall cane-like plants a metre or so high, clumped or trailing, pendent or climbing, erect or creeping, tufted and tiny, delicate moss-like species that can grow on the thinnest of twigs. But they have one common denominator: they all have two pollinia.
They have reduced their pseudobulbs and instead, some species have thick succulent leaves.
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.
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.
This is a long list, with about 1240 species. See List of Pleurothallis species.
A few have common names :
- Pleurothallis angustifolia : Wilson's Bonnet Orchid
- Pleurothallis appendiculata : Hand Bonnet Orchid (now a synonym of Antilla appendiculata (Cogn.) Luer in 2004)
- Pleurothallis aristata : Forest Bonnet Orchid
- Pleurothallis domingensis : Guadeloupe Bonnet Orchid (now a synonym of Crocodeilanthe domingensis (Cogn.) Luer 2004)
- Pleurothallis immersa : Black Orchid - now a synonym of Specklinia immersa (Linden & Rchb.f.) Luer
- Pleurothallis oblongifolia : Ladies' Bonnet Orchid
- Pleurothallis obovata : South American Bonnet Orchid - now a synonym of Anathallis obovata
- Pleurothallis pruinosa : Waxy Bonnet Orchid
- Pleurothallis pubescens : Hairy Bonnet Orchid
- Pleurothallis ruscifolia : Green Bonnet Orchid
- Pleurothallis segoviensis : Trout-fly Orchid - now synonym of Unciferia segoviensis (Rchb.f.) Luer
- Pleurothallis sieberi: Luer
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- Luer, Carlyle; 1986 - Icones Pleurothallidinarum III: Systematics of Pleurothallis (Orchidaceae); Missouri Botanical Garden Press.
- Pridgeon, A., and M. Chase (2001). "A phylogenetic reclassification of Pleurothallidinae (Orchidaceae)". Lindleyana 16: 235–271.