Bifrenaria, abbreviated Bif. in horticultural trade, is a genus of plants in family Orchidaceae. It contains 20 species found in Panama, Trinidad and South America. There are no known uses for them, but their abundant, and at first glance artificial, flowers, make them favorites of orchid growers.
The genus can be split in two clearly distinct groups:Cogniaux, Celestin A.(1902). Bifrenaria in Flora Brasiliensis K.F.P.von Martius & auct. suc. (eds.) vol.3 p. 5: 476. published on Internet. one of highly robust plants with large flowers, that encompass the first species to be classified under the genus Bifrenaria; other of more delicate plants with smaller flowers occasionally classified as Stenocoryne or Adipe. There are two additional species that are normally classified as Bifrenaria, but which molecular analysis indicate to belong to different orchid groups entirely. One is Bifrenaria grandis which is endemic to Bolívia and which is now placed in Lacaena,Kraenzlin, Friedrich Wilhelm Ludwig (1928). While Lacaena grandis in Repertorium specierum novarum regni vegetabilis. Ed. Selbstverlag des Herausgebers, Berlin, at vol.25: 25. and Bifrenaria steyermarkii, an inhabitant of the northern Amazon Forest,Dunsterville, Galfried Clement Keyworth & Garay, Leslie A. (1976). Bifrenaria steyermarkii in Venezuelan Orchids Illustrated vol.6: 56. London. which does not have an alternative classification.
Description
Bifrenaria are generally robust plants, of sympodial growth, between ten and sixty centimeters tall. They are characterized by round-section root with thick velamen, four-angled fleshy pseudobulbs of one internode, often basally protected by dried sheaths and with only one apical leaf (except for Bifrenaria steyermarkii, which occasionally has two),Foldats, Ernesto (1970). Xylobium steyermarkii em Novedades Cientificas, Contribuciones Occasionales del Museo de Historia Natural La Salle vol.35: 1. Serie Botanica. Caracas. plicate (fan-folded) enervated leathery leaves, yet malleable and not exceedingly thick, with a pseudo-petiole of basal round section, and a basal inflorescences bearing up to ten flowers, which seldom surpass the leaves' length.
Bifrenaria flowers are strongly scented, they have sepals slightly larger than the petals, with the lateral ones basally united to the column foot forming a calcar with truncated extremity. The column is slightly arching, generally without wings or any other appendages, bearing a foot which the labellum is hinged to, whose shape varies, articulated to the column, with a longitudinal channeled callus often with a basal claw. Flowers show two elongated stipes, hardy ever one, at least twice longer than wide, with salient viscidium, visible caudicles and retinacle in inverted positions. The superposed pollinia number four, and are protected by a deciduous incumbent anther. Fruits are green, erect or pendulous; they take about eight months to ripe and hold hundreds of thousand yellowish or brownish elongated seeds up to 0.35 mm long.Dressler, Robert L. (1993). Phylogeny and classification of the orchid family. Cambridge University Press. Among all the mentioned, the main characteristic distinguishing Bifrenaria from its closest relatives is the presence of the calcar.Frederico C. Hoehne (1953). Bifrenaria in Flora Brasílica, Vol 12, 7. Instituto de Botânica de São Paulo. Other important characters are the four-sided single-leaved pseudobulbs besides the raceme inflorescence with two to ten flowers.Campacci, Marcos A. (2003). Coletânea de Orquídeas Brasileiras II, Bifrenaria. Ed. Brasil Orquídeas.
Little is known about pollination in Bifrenaria. Apparently the only existing records report the presence of some large species' pollinia observed on the back of male Eufriesea violacea bees (Euglossinae),Dressler, Robert L. (1990). The orchids natural history and classification. London: Harvard University Press. and of Bombus brasiliensis (Bombini).Singer, Rodrigo B. & Koehler, S. (2004). Pollinarium morphology and floral rewards in Brazilian Maxillariinae (Orchidaceae). Annals of Botany 93: 39–51. Although there are no reports of flower pollination being directly observed, a paper published in 2006 studied the micromorphology of the labellum in Bifrenaria species, looking for substances useful to insects as food.Davies, K.L. & Stpiczynska, M. (2006). Labellar Micromorphology of Bifrenariinae Dressler (Orchidaceae). Annals of Botany Company. Oxford University Press. published on the Internet The absence of such substances on the densely pubescent surface of most Bifrenaria labelli seems to indicate possible pollination by large bees as the major mean. Another indicator of this possibility is the strong smell emanated by species like B. tetragona which are similar to those of plants in other families which are also pollinated by these bees. The smaller pubescent species may be pollinated by smaller bees, while the smooth ones, which have strong colored flowers, as B. aureofulva, might be pollinated by hummingbirds.
Taxonomy and phylogeny
The first Bifrenaria species to be described was in 1824 by English Botanist William Jackson Hooker, under the name Dendrobium harrisoniae.Hooker, William Jackson (1824). Dendrobium harrisoniae in Exotic Flora. 2: t. 120. Edinburgh. Three years later, he also described the first small-flowered species, B. racemosa, but placed it in Maxillaria.Hooker, William Jackson (1827). Maxillaria racemosa in Botanical Magazine vol. 54: t. 2789. Curtis Ed., London. With these two publications began a long series of species descriptions and confusing genera creation which generated much doubt for the next two centuries. The Royal Botanic Gardens, Kew registers the submission of 69 species or subspecific taxa under Bifrenaria since the description of the first species. Among these, twenty are generally accepted but only seventeen are truly well established, with no doubts about their limits and classification. Thirteen other species are still accepted but now placed in other genera, and four or five, due to deficiencies in their descriptions, might never be definitely identified.
In 1832, John Lindley proposed the genus Bifrenaria and described its type species, Bifrenaria atropurpurea,Lindley, John (1832). Bifrenaria in The Genera and Species of Orchidaceous Plants: 152. previously named by Conrad Loddiges as Maxillaria atropurpurea.Loddiges, Conrad L. (1832). Maxillaria atropurpurea em Botanical Cabinet vol.19: t.1877. London. The name Bifrenaria comes from bi, two, and freno, brake, a reference to the shape of the two pairs of pollinia hold by separated caudicles presented by its flowers.
In 1837, Constantine Samuel Rafinesque, considering the noticeable vegetative difference between the few Bifrenaria known at the time, proposed the genus Adipe, based on B. racemosa morphology, described by Hooker few years before, to which he added the description of a supposed new species, Adipe fulva (today treated as a synonym of B. racemosa).Rafinesque, Constantine Samuel (1837). Adipe in Flora Telluriana vol. 2: 101. The next year Lindley received a specimen from Amazonia, which was morphologically even more distant from the known species, but nonetheless described it as Bifrenaria longicornis'''. Five years later, apparently not aware of Rafinesque's previous genus Adipe, Lindley changed his mind and suggested that this species should be classified under a new genus, Stenocoryne.Lindley, John (1843). Stenocoryne in Edwards's botanical register 29(Misc.): 53 Ed. James Ridgway, London. Six species were subsequently attributed to Stenocoryne by various taxonomists, but the genus Rafinesque proposed remained unused until 1990. Wolff M.(1990)"Adipe Raf., ein 'vergessener Name.'" Die Orchidee 41:35–37.
Two species similar to Bifrenaria, but that showed a highly salient claw at the base of the labellum and lateral lobes abruptly divided were then classified under this genus. In 1914, Rudolf Schlechter suggested they should be classified under the genus Lindleyella, with Lindley's Bifrenaria aurantiaca (which presented the mentioned differences) as the type. However this genus name was already occupied (It is a synonym of Lindleya, in the Rosaceae).Schlechter, Rudolf (1914). Lindleyella in Orchideen: 414. Just thirty years later, in 1944, Frederico Carlos Hoehne, working on the first revision of genus Bifrenaria, corrected the suggestion of Schlechter. Hoehne initially proposed the genus Schlechterella for these species but, coincidentally, this name was also taken, this time by African Asclepiadaceae.Hoehne, Frederico Carlos (1944). Schlechterella in Arquivos de Botânica de Estado São Paulo, n.s., f.m., 2: 13. Finally a genus with an available name in homage to Schlechter was erected in the very next issue of the journal, Rudolfiella, by which time the number of species had increased to seven. On this revision, besides Rudolfiella, Hoehne divided Bifrenaria into two genera, accepting Lindley's Stenocoryne but calling attention to the existence of Rafinesque's Adipe, which should have nomenclatural priority, while also raising doubts about the identity of several described species.Hoehne, Frederico Carlos (1944). Rudolfiella in Arquivos de Botânica de Estado São Paulo, n.s., f.m., 2: 14. In 1990, Manfred Wolff formally resurrected the genus Adipe and transferred to it ten Bifrenaria species, besides the two already described by Rafinesque; his change was purely nomenclatural and he did not revisit the species.Koehler, S., N. H. Williams, W. M. Whitten & M. C. E. Amaral. (2002) "Phylogeny of the Bifrenaria (Orchidaceae) complex based on morphology and sequence data from nuclear rDNA internal transcribed spacers (ITS) and chloroplast trnL-trnF region." International Journal of Plant Sciences 163:1055-1066
Making the picture even more complex, in 1994, Karheinz Senghas, based on several characteristics shared only by B. tetragona and B. wittigii, described the genus Cydoniorchis to accommodate them.Senghas, Karlheinz (1994). Cydoniorchis em Journal für den Orchideenfreund 1: 11. In 1996, Gustavo Romero and Germán Carnevali transferred to Bifrenaria a species originally described by Schlechter as Maxillaria petiolaris and now classified as Hylaeorchis petiolaris.Romero, Gustavo A. & Carnevali, German (1996). Bifrenaria petiolaris em Richard Spruce: Botanist and Explorer 180. On the same year, Vitorino Castro Neto published a revision of Bifrenaria, with five sections, which is the classification generally used today.Castro Neto, Vitorino P. (1996). Contribution to the study of the genus Bifrenaria. Proceedings of the 15th World Orchid Conference. Turriers, Naturalia Publications, Rio de Janeiro, pp. 376-383.Bifrenaria has traditionally been classified in subtribe Bifrenariinae of tribe Maxillarieae (Epidendroideae), however, the relationships among the several genera within this tribe are not well defined and changes are expected in the upcoming years. The genus closest to Bifrenaria is Rudolfiella. Other related genera are Teuscheria, Guanchezia, Hylaeorchis and Horvatia, in addition to the more distant Scuticaria and Xylobium. The unification of subtribes Lycastinae, Maxillariinae and Bifrenariinae has recently been suggested. However, there is no consensus on the path to be followed.Whitten, W. Mark, Williams, Norris H. & Chase, Mark W. (2000). Subtribal and generic relationships of Maxillarieae (Orchidaceae) with emphasis on Stanhopeinae: combined molecular evidence. American Journal of Botany. 2000;87:1842-1856. Published on the Internet Contrary to what was previously thought, the relationship among Bifrenaria and all these genera from Central America seems to indicate a primitive origin of Bifrenaria in Central America and its posterior dissemination towards the Southeast of Brazil, where it found fertile grounds to its more recent evolution.