Bignoniaceae
Bignoniaceae is a family of flowering plants in the order Lamiales commonly known as the bignonias or trumpet vines. It is not known to which of the other families in the order it is most closely related.
Nearly all of the Bignoniaceae are woody plants, but a few are subwoody, either as vines or subshrubs. A few more are herbaceous plants of high-elevation montane habitats, in three exclusively herbaceous genera: Tourrettia, Argylia, and Incarvillea. The family includes many lianas, climbing by tendrils, by twining, or rarely, by aerial roots. The largest tribe in the family, called Bignonieae, consists mostly of lianas and is noted for its unique wood anatomy.
The family has a nearly cosmopolitan distribution, but is mostly tropical, with a few species native to the temperate zones. Its greatest diversity is in northern South America. The family has been covered in some major floristic projects, such as Flora of China, Flora Malesiana, and Flora Neotropica. It has not yet been covered in some others, such as Flora of Australia, and Flora of North America.
Bignoniaceae are most noted for ornamentals, such as Jacaranda, Tabebuia and Spathodea, grown for their conspicuous, tubular flowers. A great many species are known in cultivation. Various other uses have been made of members of this family. Several species were of great importance to the indigenous peoples of the American tropics. Fridericia elegans, Tanaecium bilabiata, and Tanaecium excitosum are poisonous to livestock and have caused severe losses.
According to different accounts, the number of species in the family is about 810 or about 860. The last monograph of the entire family was published in 2004. In that work, 104 genera were recognized. Since that time, molecular phylogenetic studies have greatly clarified relationships within the family, and the number of accepted genera is now between 80 and 85.
Description
Members of this family are mostly trees or lianas, sometimes shrubs, and rarely subshrubs or herbs.Lianas of the tribe Bignonieae have a unique vascular structure, in which phloem arms extend downward into the xylem because certain segments of the cambium cease the production of xylem at an early stage of development. The number of these arms is four or a multiple thereof, up to 32. When four, the phloem arms appear as a cross, hence, the common name "cross vine". The phloem in the arms has wider sieve tubes and less parenchyma than the ordinary phloem.
The leaves are petiolate. Leaf arrangement usually is opposite, or rarely alternate or verticillate. Leaves are usually compound, bifoliate, trifoliate, pinnate, or palmate, or rarely simple. Stipules are absent, but persistent; enlarged axillary bud scales are often present. Domatia occur in some genera.
File:Dolichandrone falcata W2 IMG 9458.jpg|thumb|left|190px|Dolichandrone falcata in Hyderabad, India
Flowers are solitary or in inflorescences in a raceme or a helicoid or dichasial cyme. Inflorescences bear persistent or deciduous bracts or bractlets.
The flowers are hypogynous, zygomorphic, bisexual, and usually conspicuous. The calyx and corolla are distinct. The calyx is synsepalous, with five sepals. The corolla is sympetalous, with five petals, often bilabiate. Corolla lobes are imbricate in bud, or rarely valvate, and usually much shorter than the corolla tube. Stamens are inserted on the corolla tube, alternating with corolla lobes. The four stamens are didynamous, members of each pair often connivent, the adaxial stamen is usually staminodial or absent; rarely with five fertile stamens or with two fertile and three staminodial stamens. The stigma is bilobed, and usually sensitive; a style is present. The ovary is superior, usually surrounded by a nectary disk, composed of two carpels, bilocular and with a septum, except unilocular in Tourrettia and quadrilocular in Eccremocarpus. Placentation is axile, except parietal in Tourrettia. Ovules are numerous.
The fruit is usually a bivalved capsule, often with a replum. Dehiscence is septicidal or loculicidal. The three exceptions are the genera Kigelia, Crescentia and their close relatives, and Colea and its close relatives. In these, the fruit is indehiscent, not a capsule, and the seeds are not winged. The fruit is a berry in these genera. Seeds are usually flat and winged. Aril is absent. Endosperm usually absent, and sometimes sparse.
Lapachol, a yellow, skin-irritating naphthoquinone, is often found in the wood. Other naphthoquinones, as well as anthraquinones, are also present in various parts of the plant. Jacaranone is a quinonoid from Jacaranda. True tannins are not present. Pigments are mostly flavones, anthocyanins, and carotenoids. Iridoids are usually present. Other compounds detected in Bignoniaceae include verbascosides, cornoside, quercetin, ursolic acid, saponins, and catalpic acid.
The chromosome number does not vary much in Bignoniaceae. The haploid is 20 for nearly every species sampled, but some species have very small chromosomes, making an accurate count difficult. B chromosomes are common in Bignoniaceae.
Pollination is either entomophilous, ornithophilous, or chiropterophilous.
Taxonomy
The family Bignoniaceae was first validly published in the botanical literature by Antoine Laurent de Jussieu in 1789 in his classic work, Genera Plantarum. The type genus for this family is Bignonia, which was validated by Linnaeus in Species Plantarum in 1753. The name originated with Joseph Pitton de Tournefort, who named it for his benefactor, Jean-Paul Bignon, in 1694, in his influential Eléments de botanique ou méthode pour connaître les plantes.Important groundwork for future study of the family was laid down from 1789 to 1837, mostly by Jussieu, Kunth, Bojer and G.Don not George Don the elder. Bentham and Hooker surveyed the family in their Genera Plantarum in 1876. Karl Moritz Schumann wrote a monograph on Bignoniaceae in 1894 for Engler and Prantl's Die Natürlichen Pflanzenfamilien. After Schumann's monograph, no taxonomic treatment of the entire family was published until 2004.
As the number of known species gradually increased, a great deal of confusion developed over the delimitation of genera. New genera were frequently erected for species that did not clearly belong to any of the previously described genera. This resulted in a proliferation of monotypic genera. Gentry reduced the number of genera in 1973, 1976, and 1979. Nevertheless, the revision of 2004 described 104 genera, 38 of them monotypic.
This problem was especially acute in the tribe Bignonieae. In that tribe, many species of uncertain affinity were assigned to a vaguely defined Arrabidaea, turning that genus into a "wastebasket" of about 100 species.
Since 2004, molecular phylogenetic studies have shown a substantial revision of the genera is necessary. Much work toward this goal can be viewed online, but little of it has yet been published in scientific papers.
A detailed taxonomic history of Bignoniaceae was published in 1980. A summary of this history was published in 1999.
Classification
In the APG IV system of classification for flowering plants, Bignoniaceae is one of the 24 families in the order Lamiales.. Within the order, Bignoniaceae is in a group of eight families consisting of Thomandersiaceae, Pedaliaceae, Martyniaceae, Schlegeliaceae, Bignoniaceae, Verbenaceae, Acanthaceae, and Lentibulariaceae. This group is described as a polytomy, meaning no two of its members are known to be more closely related to each other than to any of the others. Statistical support for this group remains weak, indicating insufficient data have been applied, or the group is an artifact of some phylogenetic method.The composition of Bignoniaceae has been relatively stable and has not varied at all in the 21st century. In the 20th century, the only issues of circumscription were whether Paulowniaceae and Schlegeliaceae should be merged into Bignoniaceae, or accepted as separate families. The Paulowniaceae consist of one to four genera: Paulownia, Shiuyinghua, Wightia, and Brandisia. Whatever their circumscription, Paulowniaceae are now known to be close to Phrymaceae and Orobanchaceae, rather than to Bignoniaceae. The family Schlegeliaceae has been included in Bignoniaceae, as tribe Schlegelieae, as recently as 1980. It is now accepted as a distinct family, but its relationships with several other families remain unresolved.
In molecular phylogenetic analyses, Bignoniaceae has surprisingly weak bootstrap support, given its morphological coherence. The tribe Jacarandeae is sister to the rest of the family, which is known as the Core Bignoniaceae. The Core Bignoniaceae is strongly supported in all molecular phylogenetic analyses, but has no known morphological synapomorphy.
No subfamilies have been proposed for Bignoniaceae in recent taxonomy, but in 2004, Fischer et al. divided the family into seven tribes: Tourrettieae, Eccremocarpeae, Tecomeae, Bignonieae, Oroxyleae, Crescentieae, and Coleeae. Since that time, Tourrettieae and Eccremocarpeae have been merged under the name Tourrettieae. Tecomeae sensu lato has been shown to be polyphyletic, consisting of the following groups: Astianthus, Jacarandeae, Argylia, Delostoma, Perianthomega, Catalpeae, Tecomeae sensu stricto, and all of Crescentiina except those genera placed in Crescentieae or Coleeae. All of these groups are monophyletic except Crescentiina pro parte. The whole Crescentiina is monophyletic. Crescentiina is one of a type of name with no definite taxonomic rank. Crescentiina is composed of two strongly supported clades, informally named the Tabebuia alliance and the Paleotropical clade. The tribe Crescentieae is embedded in the Tabebuia alliance and might be expanded to include Spirotecoma. Coleeae sensu Fischer et al. is polyphyletic because of the inclusion of Kigelia, and it is nested within the Paleotropical clade. Perianthomega has been transferred from Tecomeae sensu stricto to Bignonieae, where it is sister to the remainder of the tribe. Thus, Bignoniaceae can be divided into 10 monophyletic groups.