Describe head inflorescence

Explanation

Head: A head is a characteristic inflorescence of Asteraceae and is also found in some members of Rubiaceae. Example: Neolamarkia cadamba and Mitragyna parvifolia, and in some members of Fabaceae-Mimosoideae, example: Acacia nilotica, Albizia lebbeck, Mimosa pudica (sensitive plant). Torus contains two types of florets: 1. Disc floret or tubular floret. 2. Ray floret or ligulate floret.
Heads are classified into two types:
(i) Homogamous head: This type of inflorescence exhibits single kind of florets. Inflorescence has disc florets alone. Example: Vernonia, Ageratum or Ray florets alone, example: Launaea, Sonchus.
(ii) Heterogamous head: The inflorescence possesses both types of florets. Example: Helianthus, Tridax.
Disc florets at the centre of the head are tubular and bisexual whereas the ray florets found at the margin of the head which are ligulate pistilate (unisexual).