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Bignoniaceae

Family of flowering plants

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  • 3 chapters

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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 (in whorls). Leaves are usually compound, bifoliate, trifoliate, pinnate, or palmate, or rarely simple. Stipules are absent, but persistent; enlarged axillary bud scales (pseudostipules) are often present. Domatia occur in some genera.

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 (base chromosome number) 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 (via insects), ornithophilous (via birds), or chiropterophilous (via bats).

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