In a flowering plant, a cluster of flowers on its branches is called an inflorescence. There are different inflorescence types based on the arrangement of flowers on a stem or its central axis, which is also termed peduncle. Based on this arrangement of flowers, inflorescence is classified as – indeterminate and determinate.
In the former, the youngest buds are either in the centre of its truncated axis or at the top of its elongated stem. In determinate inflorescence, these budding flowers are either at the bottom of an elongated axis or outside a truncated axis. Consequently, in determinate inflorescence flowers start maturing from the top down or inside out, while in indeterminate inflorescence they mature from bottom to top or outside in.
Under these two broad categories, inflorescences are further divided into several types. These are – racemose inflorescence, Cymose, compound, mixed and special inflorescence.
Racemose Inflorescence in Detail
This is a type of inflorescence where the central axis or the peduncle continues to grow, and the flowers are stalked laterally in an acropetal order. Acropetal order means that flowers at the bottom are older than the ones on the top. Flowers can also be seen arranged in a centripetal order. Consequently, it belongs to the indefinite inflorescence category. Moreover, it is also called indefinite or infinite type as its main stem grows continuously.
Racemose inflorescence is further divided into several types based on the following classification.
The central axis is short.
The main axis is flat.
The main axis is elongated.
Types of Racemose Inflorescence
The following types of racemose inflorescence are vital as a part of your curricula. Notably, these can be broadly divided into ten major categories which are explained below in detail.
Raceme – In this type of inflorescence, the central axis is elongated, and therefore the flowers grow on a short stalk which is called the pedicel. There is an unbranched central axis growing between the branch and stem of leaves where these flowers develop. Examples of such flowers are mustard, crotalaria etc.
Panicle – An inflorescent which has several branches is called a panicle. It is a type of raceme inflorescence where the branches are also raceme. It can be either determinate or indeterminate. Some plants which fall under this category are pistachio, oat, crabgrass etc.
Corymb – In this inflorescent, the central axis is short. It has a very interesting structure. Its branching system is like a panicle and its top looks like an umbel. The pedicles of outermost flowers are longer compared to their inner ones so that all the flowers are on the same level.
Spike - It is similar to raceme inflorescence as it is also unbranched and an indeterminate. But it does not have a pedicel; instead, the flowers emerge directly from the stem. Flowers that are attached to the stem and have no stalk are called sessile flowers. Malabar nut and chaff flowers are some of the few spike inflorescence.
Spikelet – As the name suggests, spikelet is tiny spikes. It consists of florets called the rachilla. Each floret contains lemma, palea, lodicules, stamens and pistils which are enclosed in two bracts. This type of inflorescence can be seen commonly in grass flowers.
Catkin – Elongated flowers clustered in spiral or whorled arrangement with minimal or no petals are known as a catkin. Pollens are carried from male flowers to female flowers or vice versa for pollination. These flower clusters are observed on trees like willow, oaks, birches etc.
Spadix – It is a type of cylindrical shaped spike inflorescence. The florets are arranged around a fleshy axis. Its base is covered by a large brightly coloured leaf which is known as the spathe. Its function in a spadix inflorescence is to attract insect pollinators along with protecting the spadix.
Umbel – This is an instance of inflorescence with a shortened stem. However, its flowers are all of the same lengths and arranged at their top which gives plants of these species an umbrella-like look.
Capitulum – It also belongs to the category of inflorescence with the shortened main stem. Some of its characteristics are – its flowers are packed tightly together, and it has no stalk. It also develops from a flattened central axis. It has two types of florets – ray florets at the peripheral and disc florets in the centre. Some examples of capitulum inflorescences are marigolds, sunflowers, dahlia and other plants from the sunflower family.
Capitate – This type of racemose inflorescence has a globose structure. Apart from that, it has tightly clustered sessile flowers growing on a compressed rachis. For instance, Mimosa pudica belongs to the capitate inflorescence family.
All the best for NEET!
NEET is an all India based entrance examination for entrance to medical courses in prestigious colleges. Since the examination is almost around the corner, you are probably halfway with your revision. Make sure you are focusing equally on all the critical concepts such as racemose inflorescence.
Along with that, do not forget to go through previous years’ question papers to have an idea about the question pattern and structure. Appear for regular mock tests to ascertain your strength and weakness. You can also avail NEET study materials and practise questions on topics like inflorescence types which will help you with a quick revision.
Best of luck for NEET!
1. What is racemose inflorescence?
Ans. The type of inflorescence where the central axis continues to grow, and flowers are arranged laterally either in acropetal or centripetal order is called a racemose inflorescence. Examples of this type of inflorescence include mustard, barley, wheat etc.
2. What is acropetal and centripetal succession?
Ans. In acropetal succession, the flowers at the bottom of the stem are older, and younger ones are at the top. Similarly, in centripetal succession, the flowers on the edge mature first compared to those closer to the centre.
3. How is racemose inflorescence different from cymose inflorescence?
Ans. In racemose inflorescence, the central axis continues to grow whereas, in a cymose inflorescence, the peduncle ends into a single flower.