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Inflorescences
The inflorescence is the flowering part of the plant.
There are two major classes of inflorescences: terminal, in which the inflorescence terminates the shoot and axillary, in which the inflorescence is found in the axil of a leaf.
Inflorescence Parts [Illustration]
An inflorescence is composed of several different parts:
- Floret: The smallest unit of an inflorescence. In grasses, it is composed of a flower and two bracts called the palea and lemma.
- Pedicel: The portion of stem immediately below a flower (or spikelet in grasses).
- Peduncle: The portion of stem above the leaves and below the lowest branching point of the inflorescence. Or, in a single-flowered inflorescence, the portion of stem below the flower and above the leaves.
- Rachis: The main stem portion of an inflorescence above the peduncle and below the pedicels.
- Ray: The outermost flowers of a composite inflorescence. Rays often look like petals of a flower.
- Scape: A leafless stem arising at ground level and ending at the inflorescence. The term is equivalent to peduncle but only for plants with basal leaves.
- Spathe: A large bract beneath and enclosing the inflorescence.
Types of Inflorescences [Illustration]
Inflorescences are some of the most complex parts of a plant to describe. There are many small differences and exceptions to common definitions. Some of the more common inflorescence types are:
- Capitulum: An inflorescence in which the flowers are found on a flattened surface called a receptacle. This is the type of inflorescence found in the sunflower family (Asteraceae).
- Catkin: A pendulous spike of reduced flowers. Catkins are adapted to wind pollination; they dangle down from the branch and blow in the wind, allowing the pollen to be freely dispersed. Oaks and birches have catkins.
- Cauliflory: Having inflorescences on the stem of a tree. This is the type of inflorescence found in the native redbud tree (Cercis canadensis).
- Corymb: A flat-topped raceme; the lower branches of the raceme are long and the upper branches are short so that the overall shape is flat. Bridal-wreath Spiraea x van houttei is an example of a plant with corymbose inflorescences.
- Cyme: An inflorescence that terminates in a flower, and lateral branches arising below this flower also terminate in flowers. Usually, the flower at the end of the central shoot blooms first, with additional flower buds opening in sequence, from inside out. Wild pink (Silene caroliniana) bears cymes.
- Fascicle: An inflorescence with a very short shoot and long pedicels, so that it appears as if a cluster of flowers arises from a single point. Common cherries (Prunus domestica) are borne on fascicles.
- Panicle: A raceme in which the lateral branches are themselves branched. Kentucky bluegrass (Poa pratensis) has spikelets in panicles.
- Raceme: An unbranched, elongated shoot with lateral flowers that mature from the bottom upwards. Black cherry (Prunus serotina) has racemose inflorescences.
- Single flower: An inflorescence composed of a single flower. Tulips have single-flowered inflorescences.
- Spadix: A spike with small flowers crowded on a fleshy axis, characteristic of the Araceae (Jack-in-the-pulpit family).
- Spike: A raceme with unstalked flowers maturing from the bottom upwards. Wheat (Triticum aestivum) has spike-form inflorescences.
- Umbel: A flat-topped inflorescence in which the pedicels all originate from a single point, much like the struts of an umbrella. Queen-Anne's-lace (Daucus carota) has umbelliform inflorescences.