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The pattern of division of a leaf into discrete components or segments is termed leaf type.
Based on the number of segments
A leaf is said to be simple when the petiole bears a single lamina; lamina may be entire (undivided) Example: Mango or incised to any depth but not upto the midrib or petiole. Example: Cucurbita.
Compound leaf is one in which the main rachis bears more than one lamina surface, called leaflets. Compound leaves have evolved to increase total lamina surface. There is one axillary bud in the axil of the whole compound leaf. The leaflets however, do not possess axillary buds.
A pinnately compound leaf is defined as one in which the rachis, bears laterally a number of leaflets, arranged alternately or in an opposite manner, as in tamarind, Cassia.
i. Unipinnate: The rachis is simple and unbranched which bears leaflets directly on its sides in alternate or opposite manner. Example: Rose, Neem. Unipinnate leaves are of two types.
· when the leaflets are even in number, the leaf is said to be paripinnate. Example: Tamarindus, Abrus, Sesbania, Saraca, Cassia.
· when the leaflets are odd in number, the leaf is said to be imparipinnate. Example: Rosa, Azadirachta (Neem), (Murraya Chinese box).
i. Bipinnate: The primary rachis produces secondary rachii which bear the leaflets. The secondary rachii are known as pinnae. Number of pinnae varies depending on the species. Example: Delonix, Mimosa, Acacia nilotica, Caesalpinia.
ii. Tripinnate: When the rachis branches thrice the leaf is called tripinnate. (i.e) the secondary rachii produce the tertiary rachii which bear the leaflets. Example: Moringa, Oroxylum.
iii. Decompound: When the rachis of leaf is branched several times it is called decompound. Example: Daucus carota, Coriandrum sativum, Foeniculum vulgare.
A palmately compound leaf is defined as one in which the petiole bears terminally, one or more leaflets which seem to be radiating from a common point like fingers from the palm.
i. Unifoliolate: When a single leaflet is articulated to the petiole is said to be unifoliolate. Example: Citrus, Des modium gangeticum.
ii. Bifoliolate: When there are two leaflets articulated to the petiole it is said to be bifoliolate. Example: Balanites roxburghii, Hardwickia binata, Zornia diphylla
iii. Trifoliolate: There are three leaflets articulated to the petiole it is said to be trifoliolate. Example: wood apple (Aegle marmelos), Clover (Trifolium), Lablab, Oxalis
iv. Quadrifoliolate: There are four leaflets articulated to the petiole it is said to be quadrifoliolate. Example: Paris quadrifolia, Marsilia
v. Multifoliolate or digitate: Five or more leaflets are joined and spread like fingers from the palm, as in Ceiba pentandra, Cleome pentaphylla, Bombax ceiba
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