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:
1. 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.
2. 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).
