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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 usually different from foliage leaves. They may be smaller, larger, or of a different color, shape, or texture. Typically, they also look different from the parts of the flower, such as the petals or sepals. A plant having bracts is referred to as bracteate or bracteolate, while one that lacks them is referred to as ebracteate and ebracteolate, without bracts.
Some bracts are brightly-coloured and serve the function of attracting pollinators, either together with the perianth or instead of it. Examples of this type of bract include those of Euphorbia pulcherrima (poinsettia) and Bougainvillea: both of these have large colourful bracts surrounding much smaller, less colourful 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.
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. Beggar-tick (Bidens comosa) has narrow involucral bracts surrounding each inflorescence, each of which also has a single bract below it. There is then a pair of leafy bracts on the main stem and below those a pair of leaves.
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 in them. They are present in the hibiscus family, Malvaceae. Fragaria (strawberries) may or may not have an epicalyx.
A spathe is a large bract or pair of bracts forming a sheath to enclose the flower cluster of such plants as palms, arums, irises, crocuses, and dayflowers (Commelina). Zephyranthes tubispatha in the Amaryllidaceae derives its specific name from its tubular spathe. In many arums (family Araceae), the spathe is petal-like, attracting pollinators to the flowers arranged on a type of spike called a spadix.
Reproductive transition of grasses is characterized by switching the pattern of lateral branches, featuring the suppression of outgrowth of the subtending leaves (bracts) and rapid formation of higher-order branches in the inflorescence (panicle). However, the molecular mechanisms underlying such changes remain largely unknown. Here, we show that bract suppression is required for the reproductive branching in rice. We identified a pathway involving the intrinsic time ruler microRNA156/529, their targets SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) genes, NECK LEAF1 (NL1), and PLASTOCHRON1 (PLA1), which regulates the bract outgrowth and thus affects the pattern switch between vegetative and reproductive branching. Suppression of the bract results in global reprogramming of transcriptome and chromatin accessibility following the reproductive transition, while these processes are largely dysregulated in the mutants of these genes. These discoveries contribute to our understanding of the dynamic plant architecture and provide novel insights for improving crop yields.
Suppression of inflorescence leaf, or bract, growth has evolved multiple times in diverse angiosperm lineages, including the Poaceae and Brassicaceae. Studies of Arabidopsis thaliana mutants have revealed several genes involved in bract suppression, but it is not known if these genes play a similar role in other plants with suppressed bracts. We identified maize (Zea mays) tassel sheath (tsh) mutants, characterized by the loss of bract suppression, that comprise five loci (tsh1-tsh5). We used map-based cloning to identify Tsh1 and found that it encodes a GATA zinc-finger protein, a close homolog of HANABA TARANU (HAN) of Arabidopsis. The bract suppression function of Tsh1 is conserved throughout the grass family, as we demonstrate that the rice (Oryza sativa) NECK LEAF1 (NL1) and barley (Hordeum vulgare) THIRD OUTER GLUME (TRD) genes are orthologous with Tsh1. Interestingly, NL1/Tsh1/TRD expression and function are not conserved with HAN. The existence of paralogous NL1/Tsh1/TRD-like genes in the grasses indicates that the NL1/Tsh1/TRD lineage was created by recent duplications that may have facilitated its neofunctionalization. A comparison with the Arabidopsis genes regulating bract suppression further supports the hypothesis that the convergent evolution of bract suppression in the Poaceae involved recruitment of a distinct genetic pathway.
The showy colors of the poinsettias are not flowers. They are actually modified leaves called bracts. The actual flowers are the yellow centers of the bracts. When grown naturally in its native setting, the plant is a large shrub or small tree that grows up to 10 to 15 feet high. As a potted plant, they usually only grow 1 to 2 feet tall.
Temperature has a direct effect on bract expansion, color, maturity and durability. Night temperatures are critical for bract expansion, with 65 to 68F (18 to 20C) being ideal for most varieties. Higher night temperatures can encourage weak bracts, dull color, bract edge problems and foliar diseases. Night temperatures that are too cool can cause bracts not to size up properly. White-flowering varieties can also look green or yellow if night temperatures are too cool. Day temperatures should be kept relatively cool to reduce stretch and increase stem strength.
Average daily temperature (ADT) has the largest impact on the rate of bract expansion and saleable color date. The stage of bract development is the best indicator of when to change temperature requirements (Table 1). Stage 3 should begin when bracts are ~75% of finished size. Stage 4 represents the time when bracts are nearly fully expanded or at saleable quality.
For example, early-flowering varieties may enter Stages 3 and 4 up to two weeks earlier than Table 1 indicates. Temperatures below 60F (15C) in Stage 4 can increase the risk of Botrytis on bracts. Maintaining dry air during the last stage when the coolest temperatures occur may be difficult with reduced heat. Cooler air temperatures increase the relative humidity in the plant canopy, which in turn makes condensation more likely. Free moisture on plant surfaces favors Botrytis development.
During the end of the season, healthy bract development is key to a quality product and long-term shelf life. The biggest issues to look out for are Botrytis and bract edge burn, which can go hand in hand. Botrytis is a quickly spreading fungal pathogen that can propagate in damaged material caused by bract edge burn. Bract edge burn is caused by a calcium deficiency.
Inadequate bract expansion can be caused by a number of reasons, including but not limited to: a lower-than-ideal ADT and excessive or late applications of PGRs. Foliar sprays of Fascination can be successful in increasing bract expansion, but carry certain risks. Over-applications of Fascination at this stage of development can lead to weakened petioles, overly large floppy bracts, a change in bract color and accelerated cyathia abscission.
Once poinsettias have essentially stopped vegetative growth and put their efforts into flowering, their overall nutrient requirements should be cut in half. Applying too much fertilizer during the bract development stage can lead to off-colored bracts, salt stress and disease issues, such as Botrytis and Pythium. Please refer to Table 2 for general recommended feed rates based on dates during the late season.
Nutrient deficiencies that do occur during the later portion of the season need to be corrected immediately to prevent a decrease in plant quality. Most of these issues can be prevented by making sure your crop is appropriately fed and soil pH is in the correct range leading into flower. We recommend testing your tissue and soil prior to first color in order to correct any issues before bracts begin developing.
Palea In the sunflower family (Asteraceae), a small bract at the base of a disk floret; in the grass family (Poaceae), the upper of two bracts at the base of a floret; the lower is the lemma Image .
A whorl of stalkless flowers around the tip of a thick spike at the end of branching stems. Flowers are 1/8-inch across with 5 light blue to purple to pink petals fused at the base forming a slender tube. The petal lobes are unequal in size, the 2 upper slightly smaller than the lower 3. The mouth of the tube and into the throat is white; hidden inside the tube are 4 stamens and a short style. The calyx has 5 sharply pointed lobes and is nearly as long as the floral tube. At the base of each flower is a narrow leaf-like bract, lance-linear and up to ¾ inch long. Bracts and calyx are densely covered in stiff hairs. The spikes enlongate to 6 inches or more, with flowers blooming at the tip and fruit forming below. 781b155fdc