Leaf Variation and Specialization

• Bracts: leaf tissue, looks different than foliage (like bud scales), can have different functions

• Spines: leaves (in the node) that are sharp and needlelike (cactus)

• Stipules:

  • part of a leaf

  • always paired

  • located at the petiole base or an adjacent twig

Specialized leaves: bracts

• like dogwood “flowers”

• 

Specialized leaves: spines

• like cactus needles

• 

  • coming out of a bud

Specialized leaves: stipules

• Stipules

  • part of a leaf

  • always paired

  • located at the petiole base or an adjacent twig

  • 

Leaves are variable, sometimes even on the same tree!

• Heterophylly: variously leaved

• Shade versus sun leaves

  • pictures in texts are usually adult, sun leaves

  • Shade leaves: larger surface area to catch more sunlight, thinner

  • Sun leaves: reduced, thicker

• Age differences

Vestiture

• Leaf vestiture: terms describing the leaf surface

• Can apply to the surface or the underside of the leaf

• The same terms can be used to describe other parts, like petioles and twigs

• Trichomes: hairs

• 

• pubescent: often used generally to mean “hairy” but means fine, soft, short hairs

• tomentose: dense, curly, wooly hairs

• scabrous: rough, like sandpaper, with short bristly hairs

• hirsute: long, stiff trichomes

• hispid: very long, stiff trichomes

• strigose: coarse, bent trichomes with large base

Leaf vestiture: other features

• Other vestiture

  • glabrous: smooth, without any hairs

  • glaucous: waxy, often white or blue green

  • glandular: has hairs with glands, either sessile or stalked

• Where to look:

  • leaf undersides

  • along the midrib