Bract
From Wikipedia, the free encyclopedia
 |
This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2007) |
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis, or cone scale. Bracts are often (but not always) different from foliage leaves, being smaller or of a different color or texture.
Some bracts are brightly colored and serve the function of attracting pollinators, either in concert with or instead of the perianth. An excellent example of this latter type of bract occurs in the Poinsettia plant (Euphorbia pulcherrima), which has small green flowers, surrounded by large scarlet bracts.
A small bract is called a bracteole or bractlet. Technically it is any bract that arises on a pedicel instead of subtending it. In grasses, the bracts that enclose the florets are termed glumes.
Bracts that appear in a whorl subtending an inflorescence are collectively called an involucre. An involucre is a common feature beneath the inflorescences of many Apiaceae, Asteraceae, Dipsacaceae and Polygonaceae. Each flower in an inflorescence may have its own whorl of bracts, in this case called an involucel. Many asteraceous plants have bracts both at the base of each flower as well as those beneath the whole inflorescence. In this case the bracts at the flower base — chaff (paleae or receptacular bracts) — are usually minute scales or bristles, while those at the base of the inflorescence or head — the involucral bracts (phyllaries) — are often green, narrow, and leafy.
A prophyll is a leaf-like structure, such as a bracteole, subtending a single flower or pedicel. The term can also mean the lower bract on a peduncle.
A spathe is a large bract that forms a sheath to enclose the flower cluster of certain plants such as palms and arums. In many arums, the spathe is petal-like, attracting pollinators to the flowers arranged on a type of spike called a spadix.
The frequently showy pair of bracts of cyathia of Euphorbia species in subgenus Lacanthis is termed the cyathophylls.
Bracts subtend the cone scales in the seed cones of many conifers, and in some cases, such as Pseudotsuga, they extend beyond the cone scales even in mature cones.
[edit] Gallery
 Bracts on Leafy bract of Beggar-tick (Bidens comosa) |
 Bracts surrounding a banana flower stalk |
 In Bougainvillea each cluster of three flowers is surrounded by three or six more colorful bracts |
 Bright red bracts of Euphorbia pulcherrima (Poinsettia) |
 Yellow petal-like bracts of Euphorbia epithymoides |
 Euphorbia milii var. vulcanii cyathia bearing a pair of pinkish cyathophylls |
 Green bracts surrounding a sunflower bud |
 Showy white bracts of the Kousa Dogwood Cornus kousa |
 Large pink bracts of an Anthurium |
 Colourful bracts of Ananas bracteatus |
