Inflorescence

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. Because flowers facilitate plant reproduction, inflorescence characteristics are largely a result of natural selection. The stem holding the whole inflorescence is called a peduncle. The main axis (also referred to as major stem) above the peduncle bearing the flowers or secondary branches is called the rachis. The stalk of each flower in the inflorescence 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. In some species the flowers develop directly from the main stem or woody trunk, rather than from the plant's main shoot. This is called cauliflory and is found across a number of plant families. An extreme version of this is flagelliflory where long, whip-like branches grow from the main trunk to the ground and even below it. Inflorescences form directly on these branches. 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. 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. Image:Offener_Blütenstand_(inflorescence).svg|Indeterminate inflorescence with a perfect acropetal maturation Image:Offener_Blütenstand_(inflorescence)_m_K.svg|Indeterminate inflorescence with an acropetal maturation and lateral flower buds Image:Pseudoterminalbluete (inflorescence).svg|Indeterminate inflorescence with the subterminal flower to simulate the terminal one (vestige present) In determinate inflorescences, the terminal flower is usually the first to mature (precursive development), while the others tend to mature starting from the base of the stem. This pattern is called acropetal maturation. When flowers start to mature from the top of the stem, maturation is basipetal, whereas when the central mature first, maturation is divergent. Image:Akropetale Effloration (inflorescence).svg|Determinate inflorescence with acropetal maturation Image:Basipetale effloration (inflorescence).svg|Determinate inflorescence with basipetal maturation Image:Divergente effloration (inflorescence).svg|Determinate inflorescence with divergent maturation Phyllotaxis As with leaves, flowers can be arranged on the stem according to many different patterns. See 'Phyllotaxis' for in-depth descriptions. Image:Inflorescences Raceme Kwiatostan Grono.svg|Alternate flowers Image:Traube dekussiert (inflorescence).svg|Opposite flowers Similarly, the arrangement of leaves in buds is called ptyxis. When a single or a cluster of flower(s) is located at the axil of a peduncle, the location of the bract in relation to the stem holding the flowers 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. Recaulescence is the fusion of the subtending leaf with the stem holding the bud or the bud itself, 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. Image:Bluete und Tragblatt (inflorescence).svg|Flower and subtending bract Image:Türkenbund dunkel.jpg|Lilium martagon (flower and subtending bract) Image:Konkauleszenz (inflorescence).svg|Concaulescence Image:Tomato scanned.jpg|Solanum lycopersicum (concaulescence) Image:Rekauleszenz (inflorescence).svg|Recaulescence Image:Tilia cordata Owoce lipy 656.jpg|Tilia cordata (recaulescence) ==Organization==