Inflorescence

Aloe hereroensis, showing inflorescence with branched peduncle

An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed. The modifications can involve the length and the nature of the internodes and the phyllotaxis, as well as variations in the proportions, compressions, swellings, adnations, connations and reduction of main and secondary axes.Inflorescence can also be defined as the reproductive portion of a plant that bears a cluster of flowers in a specific pattern.

The stem holding the whole inflorescence is called a peduncle and the major axis (incorrectly referred to as the main stem) holding the flowers or more branches within the inflorescence is called the rachis. The stalk of each single flower is called a pedicel. A flower that is not part of an inflorescence is called a solitary flower and its stalk is also referred to as a peduncle. Any flower in an inflorescence may be referred to as a floret, especially when the individual flowers are particularly small and borne in a tight cluster, such as in a pseudanthium.The fruiting stage of an inflorescence is known as an infructescence.

Inflorescences may be simple (single) or complex (panicle). The rachis may be one of several types, including single, composite, umbel, spike or raceme.

General characteristics

Inflorescences are described by many different characteristics including how the flowers are arranged on the peduncle, the blooming order of the flowers and how different clusters of flowers are grouped within it. These terms are general representations as plants in nature can have a combination of types.

Bracts

Inflorescences usually have modified shoots foliage different from the vegetative part of the plant. Considering the broadest meaning of the term, any leaf associated with an inflorescence is called a bract. A bract is usually located at the node where the main stem of the inflorescence forms, joined to the main stem of the plant, but other bracts can exist within the inflorescence itself. They serve a variety of functions which include attracting pollinators and protecting young flowers. According to the presence or absence of bracts and their characteristics we can distinguish:

  • Ebracteate inflorescences: No bracts in the inflorescence.
  • Bracteate inflorescences: The bracts in the inflorescence are very specialised, sometimes reduced to small scales, divided or dissected.
  • Leafy inflorescences: Though often reduced in size, the bracts are unspecialised and look like the typical leaves of the plant, so that the term flowering stem is usually applied instead of inflorescence. This use is not technically correct, as, despite their 'normal' appearance, these leaves are considered, in fact, bracts, so that 'leafy inflorescence' is preferable.
  • Leafy-bracted inflorescences: Intermediate between bracteate and leafy inflorescence.

If many bracts are present and they are strictly connected to the stem, like in the family Asteraceae, the bracts might collectively be called an involucre. If the inflorescence has a second unit of bracts further up the stem, they might be called an involucel.

Terminal flower

Plant organs can grow according to two different schemes, namely monopodial or racemose and sympodial or cymose. In inflorescences these two different growth patterns are called indeterminate and determinate respectively, and indicate whether a terminal flower is formed and where flowering starts within the inflorescence.

  • Indeterminate inflorescence: Monopodial (racemose) growth. The terminal bud keeps growing and forming lateral flowers. A terminal flower is never formed.
  • Determinate inflorescence: Sympodial (cymose) growth. The terminal bud forms a terminal flower and then dies out. Other flowers then grow from lateral buds.

Indeterminate and determinate inflorescences are sometimes referred to as open and closed inflorescences respectively. The indeterminate patterning of flowers is derived from determinate flowers. It is suggested that indeterminate flowers have a common mechanism that prevents terminal flower growth. Based on phylogenetic analyses, this mechanism arose independently multiple times in different species.[1]

In an indeterminate inflorescence there is no true terminal flower and the stem usually has a rudimentary end. In many cases the last true flower formed by the terminal bud (subterminal flower) straightens up, appearing to be a terminal flower. Often a vestige of the terminal bud may be noticed higher on the stem.

In determinate inflorescences the terminal flower is usually the first to mature (precursive development), while the others tend to mature starting from the bottom of the stem. This pattern is called acropetal maturation. When flowers start to mature from the top of the stem, maturation is basipetal, while when the central mature first, divergent.

Phyllotaxis

As with leaves, flowers can be arranged on the stem according to many different patterns. See 'Phyllotaxis' for in-depth descriptions

Similarly arrangement of leaf in bud is called Ptyxis.

Metatopy

Metatopy is the placement of organs out of their normally expected position: typically metatopy occurs in inflorescences when unequal growth rates alter different areas of the axis and the organs attached to the axis.

When a single or a cluster of flower(s) is located at the axil of a bract, the location of the bract in relation to the stem holding the flower(s) is indicated by the use of different terms and may be a useful diagnostic indicator.

Typical placement of bracts include:

  • Some plants have bracts that subtend the inflorescence, where the flowers are on branched stalks; the bracts are not connected to the stalks holding the flowers, but are adnate or attached to the main stem (Adnate describes the fusing together of different unrelated parts. When the parts fused together are the same, they are connately joined.)
  • Other plants have the bracts subtend the pedicel or peduncle of single flowers.

Metatopic placement of bracts include:

  • When the bract is attached to the stem holding the flower (the pedicel or peduncle), it is said to be recaulescent; sometimes these bracts or bracteoles are highly modified and appear to be appendages of the flower calyx. Recaulescences is the fusion of the subtending leaf with the stem holding the bud or the bud itself,[2] thus the leaf or bract is adnate to the stem of flower.
  • When the formation of the bud is shifted up the stem distinctly above the subtending leaf, it is described as concaulescent.
Other Languages
العربية: نورة زهرية
asturianu: Inflorescencia
беларуская: Суквецце
български: Съцветие
bosanski: Cvat
čeština: Květenství
Deutsch: Blütenstand
eesti: Õisik
español: Inflorescencia
Esperanto: Floraro
فارسی: گل‌آذین
français: Inflorescence
Gaeilge: Bláthra
한국어: 꽃차례
հայերեն: Ծաղկաբույլ
हिन्दी: पुष्पक्रम
hornjoserbsce: Kwětnistwo
hrvatski: Cvat
Bahasa Indonesia: Bunga majemuk
italiano: Infiorescenza
עברית: תפרחת
Basa Jawa: Kembang majemuk
қазақша: Гүлшоғыр
lietuvių: Žiedynas
lumbaart: Enfiurescènsa
magyar: Virágzat
മലയാളം: പൂങ്കുല
मराठी: फुलोरा
Nederlands: Bloeiwijze
日本語: 花序
norsk nynorsk: Blomestand
oʻzbekcha/ўзбекча: Toʻpgul
polski: Kwiatostan
português: Inflorescência
română: Inflorescență
Runa Simi: Tuktu-tuktu
русский: Соцветие
Simple English: Inflorescence
slovenčina: Súkvetie
slovenščina: Socvetje
српски / srpski: Цваст
srpskohrvatski / српскохрватски: Cvast
suomi: Kukinto
українська: Суцвіття
粵語: 花序
中文: 花序