Botany - Leaves

• leaves - regarded as the flattened, lateral, outgrowth of the stem/node w/ a bud in its axil
• leaves are the primary organ of photosynthesis in plants
• leaves originate in the shoot's apical meristem as a bulge of tissue called leaf primordia
• external morphology of leaves

  • stipules
  • petioles
  • leaf bases
  • leaf blade/lamina
• stipulate - leaves w stipules
• stipules - outgrowths, usually paired at the base of some dicot leaves.
• exstipulate - leaves w/out stipules
• petiole - the stalk of the leaf which is attached to the stem
• when the petiole is absent, it is called sessile
• when petiole is present, it is called petiolate
• leaf base - the part near the petiole
• in monocots, the leaf base is expanded into a structure called leaf sheath, which partially/ completely covers the stem
• in dicots, the leaf base bears 2 lateral outgrowths known as stipules
• leaf blade/lamina - the green flattened portion which performs most of photosynthesis in the plant
• a strong/thick vein known as midrib, runs through the leaf blade from its base to the apex
• the midrib branches into thinner lateral veins that give rise to still thinner lateral veins called veinlets
• phyllotaxy

  • alternate/spiral
  • opposite
  • whorled
• alternate/spiral - single leaf is present at each node
• opposite - 2 leaves arise from each node opposite each other
• whorled - there are more than 2 leaves at each node in a circle/whorl
• leaf types

  • simple
  • compound
• simple leaf - consists of a single blade which may be entire, lobed or cleft but not down to the midrib
• compound leaf - has a blade divided into no. of segment called leaflets in various ways
• 2 types of compound leaves

  • pinnately compound
  • palmately compound
• 3 types of pinnately compound

  • unipinnate
  • bipinnate
  • tripinnate
• pinnately compound - the midrib (rachis), bears leaflets arranged in a linear sequence
• unipinnate - the leaflets are attached directly on the rachis
• bipinnate - the primary rachis branches into what is known as 2ndary rachis, to which the leaflets are attached
• tripinnate - there are rachises of the first, second and third orders. leaflets are attached to the tertiary rachis malunngay
• palmately compound - the leaflets are attached to the tip of the petiole from which they radiate
• leaf venations

  • netted/reticulate
  • parallel
• netted/reticulate - there may be one/more large veins from which smaller veins branch out and interconnect, forming a network pattern
• netted/reticulate is a characteristic of a dicot
• 2 types of netted/reticulate

  • pinnately reticulate
  • palmately reticulate
• pinnately reticulate - has one principal vein/midrib present from which smaller veins branch out in all direction in the blade
• palmately reticulate - has several large veins radiating from around the tip of the petiole
• parallel - veins run parallel to each other.
• parallel venation is a characteristics of a monocot
• crenate - w/ rounded teeth
• ciliate - w/ fine hairs