General Characteristics of an Inflorescence

Bracts

Any leaf linked with an inflorescence is called a bract. These are modified foliage distinct from the vegetative part of the plant. It is usually located at the node from where the whole inflorescence arises and is also connected to the rachis. However, bracts can exist elsewhere in an inflorescence too. Their functions include attracting pollinators and protecting young flowers. Based on the presence or absence of bracts and their characteristics inflorescence can be of the following types:

• Bracteate Inflorescence: This type of inflorescence possesses flowers that bear small reduced leaves called bracts at their base.
• Ebracteate Inflorescence: Here the flowers don’t bear bracts.
• Leafy inflorescences: In this type of inflorescence, bracts are often reduced in size and are unspecialized. However, they look like the typical leaves of the plant.
• Leafy-bracted inflorescences: This type of inflorescence is intermediate between bracteate and leafy inflorescence.

Terminal Flowers

Plant organs grow in two different ways namely monopodial/racemose and sympodial/cymose. These two types of inflorescence are different based on whether they possess a terminal flower and the position where flowering starts within the inflorescence. Terminal flowers are flowers that are found at the extremities of the stem. The two major types of inflorescence are as follows:

• Indeterminate/Racemose Inflorescence: Here the flowers are arranged in an acropetal succession which means that new flowers are added on the top and the old flowers are found at the bottom. The main axis continues to grow as there is no flower present at its tip.
• Determinate/Cymose inflorescence: Here the flowers are arranged in a basipetal succession which means that old flowers are present above the new flowers. The main axis terminates into a flower and hence does not freely grow.

Phyllotaxis

Phyllotaxy is known as the pattern of arrangement of leaves on the stem or branch. Its types are:

• Alternate: In this type, a single leaf arises at each node in an alternate manner. Eg: China rose, Mustard, Sunflower.
• Opposite: In this type of phyllotaxy, a pair of leaves arise at each node. Example: Calotropis, Guava.
• Whorled: In this type of phyllotaxy, more than two leaves arise at a node. Example: Alstonia.

Similar to leaves, the flowers can be arranged in various ways on the stem, this is known as phyllotaxis. Similarly, the arrangement of leaves in a bud is known as Ptyxis. Other plants have bracts that subtend the pedicel or peduncle of single flowers. If a bract is attached to the stem and holding the flower (the pedicel or peduncle), it is known as recaulescent whereas when the formation of the bud is shifted up the stem distinctly above the subtending leaf, it is known as concaulescent.

Angiosperms (Gr. Angion = vessel; Sperma = seed) are flowering, fruit-bearing phanerogamic, spermatophytic, and sporophytic plants. They are the most recent, most advanced, most evolved, most conspicuous, and most abundant of all the plants on this earth. The study of flowering plants is called Anthology. These plants appeared in the lower cretaceous period of the Mesozoic era about 130 million years back but flourished in the Tertiary period of the Cenozoic era. The first flowering plants appeared in the Jurassic period and monocots appeared in the Oligocene period. The first angiosperm was Archaefructus from the mid-Cretaceous. They lack archegonium which is replaced by pistil (gynaecium). They have double fertilization and endosperm of triploid nature. The male gametes are nonmotile and carried by pollen tube (siphonogamy) to avoid dependence on water for fertilization. They comprise about 12500 genera and 2.68 lakh species out of which 2.20 Lakh are dicots and 50000 are monocots. Thus dicots are more than 50% of the total plants on this earth. They show great diversity in size, form, habit, habitats, life span, and mode of nutrition. They are classified into dicotyledons and monocotyledons on the basis of the number of cotyledons. Monocots are more advanced than dicots.