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. They may be smaller, larger, or of a different color, shape, or texture. Usually, they also look different from the parts of the flower, such as the petals and/or sepals.
Variants[change | edit source]
Some bracts are brightly colored and serve the function of attracting pollinators like bees, either together with the perianth or instead of it. Examples of this type of bract include Euphorbia pulcherrima (poinsettia) and Bougainvillea: both of these have large colorful bracts surrounding much smaller, less colorful flowers.
In grasses, each floret (flower) is enclosed in a pair of papery bracts, called the lemma (lower bract) and palea (upper bract), while each spikelet (group of florets) has a further pair of bracts at its base called glumes. These bracts form the chaff removed from cereal grain during threshing and winnowing.
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.
The frequently showy pair of bracts of Euphorbia species in subgenus Lacanthis are the cyathophylls.
Bracts of Bougainvillea glabra, differ in colour from the non-bract leaves, and attract pollinators
Bracts along a banana flower stalk surround the rows of flowers
Euphorbia milii var. vulcanii cyathia bearing a pair of pinkish cyathophylls
Colourful bracts of Ananas bracteatus
Bracteole[change | edit source]
A small bract is called a bracteole or bractlet. Technically this is any bract that arises on a pedicel instead of subtending it.
Involucral bracts[change | edit source]
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. In this case they may be called chaff, paleas, or receptacular bracts and are usually minute scales or bristles. Many asteraceous plants have bracts at the base of each inflorescence.
The term involucre is also used for a highly conspicuous bract or bract pair at the base of an inflorescence. In the family Betulaceae, notably in the genera Carpinus and Corylus, the involucre is a leafy structure that protects the developing nuts.
Epicalyx[change | edit source]
An epicalyx, which forms an additional whorl around the calyx of a single flower, is a modification of bracteoles In other words, the epicalyx is a group of bracts resembling a calyx or bracteoles forming a whorl outer to the calyx. It is a calyx-like extra whorl of floral appendages. Each individual segment of the epicalyx is called an episepal because they resemble the sepals. They are present in family Malvaceae, the Hibiscus family. Fragaria (strawberries) may or may not have an epicalyx.
Spathe[change | edit source]
A spathe is a large bract that forms a sheath to enclose the flower cluster of certain plants such as palms, arums, and dayflowers. In many arums (Araceae family), the spathe is petal-like, attracting pollinators to the flowers arranged on a type of spike called a spadix.
References[change | edit source]
- Ralph Simon; Marc W. Holderied, Corinna U. Koch, Otto von Helversen. "Floral acoustics: Conspicuous echoes of a dish-shaped leaf attract bat pollinators". Science 333 (6042): 631–633. doi:10.1126/science.1204210.
- Darpan, Pratiyogita (2006, June). Competition Science Vision. Pratiyogita Darpan. p. 136.
- "epicalyx - Dictionary of botany". Botanydictionary.org. http://botanydictionary.org/epicalyx.html. Retrieved 2012-04-29.