inflorescence

—inflorescent, adj.

/in'flaw res"euhns, -floh-, -fleuh-/, n.

1. a flowering or blossoming.

2. Bot.

a. the arrangement of flowers on the axis.

b. the flowering part of a plant.

c. a flower cluster.

d. flowers collectively.

[1750-60; < NL inflorescentia < LL inflorescent- (s. of inflorescens prp. of inflorescere to BLOOM. See IN-², FLORA, -ESCENT, -ENCE]

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Cluster of flowers on one or a series of branches, which together make a large showy blossom.

Categories depend on the arrangement of flowers on an elongated main axis (peduncle) or on sub-branches from the main axis, and on the timing and position of flowering. In determinate inflorescences, the youngest flowers are at the bottom or outside (e.g., onion flowers). In indeterminate inflorescences, the youngest flowers are at the top or in the center (e.g., snapdragon, lily of the valley, and Astilbe flowers). Other indeterminate inflorescences are the dangling male and female catkins of oak trees, the spike of barley, and the flat head (capitulum) of the dandelion.

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▪ plant anatomy

Introduction

      in a flowering plant, a cluster of flowers on a branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a main axis (peduncle) and by the timing of its flowering (determinate and indeterminate).

Determinate inflorescence.

      In determinate (cymose) inflorescences, the youngest flowers are at the bottom of an elongated axis or on the outside of a truncated axis. At the time of flowering, the apical meristem (the terminal point of cell division) produces a flower bud, thus arresting the growth of the peduncle.

 A cyme is a flat-topped inflorescence in which the central flowers open first, followed by the peripheral flowers, as in the onion (genus Allium).

 A dichasium is one unit of a cyme and is characterized by a stunted central flower and two lateral flowers on elongated pedicels, as in the wood stichwort (species Stellaria nemorum).

Indeterminate inflorescence.

      In indeterminate inflorescences, the youngest flowers are at the top of an elongated axis or on the centre of a truncated axis. An indeterminate inflorescence may be a raceme, panicle, spike, catkin, corymb, umbel, spadix, or head.

 In a raceme a flower develops at the upper angle (axil) between the stem and branch of each leaf along a long, unbranched axis. Each flower is borne on a short stalk, called a pedicel. An example of a raceme is found in the snapdragon (Antirrhinum majus).

 A panicle is a branched raceme in which each branch has more than one flower, as in the astilbe (Astilbe).

 A spike is a raceme, but the flowers develop directly from the stem and are not borne on pedicels, as in barley (Hordeum).

 A catkin (or ament) is a spike in which the flowers are either male (staminate) or female (carpellate). It is usually pendulous, and the perianth may be reduced or absent, as in oaks (Quercus).

 A corymb is a raceme in which the pedicels of the lower flowers are longer than those of the upper flowers so that the inflorescence has a flat-topped appearance overall, as in hawthorn (Crataegus).

 In an umbel, each of the pedicels initiates from about the same point at the tip of the peduncle, giving the appearance of an umbrella-like shape, as in the wax flowers (Hoya).

 A spadix is a spike borne on a fleshy stem and is common in the family Araceae (e.g., Philodendron). The subtending bract is called a spathe.

 A head (capitulum) is a short dense spike in which the flowers are borne directly on a broad, flat peduncle, giving the inflorescence the appearance of a single flower, as in the dandelion (Taraxacum).

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