LEAVES, FOOD FACTORIES OF PLANTS

A LOOK AT SPECIALIZED DESIGNS AND OTHER FEATURES

Although the main function of leaves is to photosynthesize and provide food for the plant, leaves also must guard

against excessive water loss and protect themselves against predation by animals

In the following examples, you will see how modified leaves help plants survive, often in unfavorable habitats

Achillea millefolium, highly scented leaves with volatile terpenes. These leaves are also pinnately compound.

Angelica, a member of the parsley family with leaves protected by fragrant terpenes. Again compound leaves

but the leaflets have an entirely different shape

Calycanthus occidentalis, spice-scented leaves with distasteful terpenes. Note the netlike vein pattern.

The underside of yerba santa (Eriodictyon californicum) leaf with dense hairs and imbued with distasteful terpenes, both ploys to cut down on water loss

Lemon leaves covered with sunken glands that give a strong citrus odor distasteful to small insects

Scented geraniumss (Pelargonium spp.) have various scents mimicking other plants, and all are designed to

repel chewers.

Poison oak (Toxicodendron diversilobum) has urushiol throughout the plant, a substance that causes blistering

of the skin. Its adaptive relevance is not clear.

Prickly poppy (Argemone munita) protects itself by poisonous opiates as well as a heavy armor of spines

Argemone lvs w/ spines. Note the pale color which helps reflect away excess heat

Thistles (Cirsium spp.) defend themselves with a spiny armor on stems and leaves

Not a thistle at all, the genus Eryngium in the parsley family has a similar spiny armor on its leaves for similar

reasons.

Ocotillo (Fouquieria splendens) leaves forming spines from the leaf stalks or petioles

The tarweeds such as Madia sativa protect stems and leaves with glandular, fragrant hairs

Spines arming Ribes stems. Only the spiny species are referred to as gooseberries

Stinging nettle (Urtica dioica) is protected by spiny hairs that release irritating chemicals when touched

California black oak (Quercus kelloggii) leaves turn color in fall when the chlorophyll breaks down, revealing

accessory yellow and red pigments

Black oak also covers its new spring leaves with pink hairs as a warning against being distasteful.

Variegated leaves such as this Coleus have a pattern of accessory pigments, in this case red anthocyanins,

covering part of the otherwise green leaf

In this example, the creek dogwood has variegated leaves, where chlorophyll is missing in the yellow and

white portions. Such leaves are not as efficient at photosynthesis and the plants grow more slowly

Cornus nuttallii (flowering dogwood) leaves turn color in the fall and display red and pink accessory pigments before falling. The adaptation of fall color is uncertain

Dudleya farinosa produces extra red anthocyanin pigments when exposed to ample light, a protection

against too much sun.

The dudleya in the previous slide along with this Aeonium belong to water-storing plants called succulents. Here the water is stored in leaves.

This century plant or Agave americana is a giant leaf succulent whose leaves are also protected by vicious,

backward-pointing spines on their margins

Similar in appearance to agaves but not related is Aloe arborescens from South Africa. It too has succulent

leaves lined with spines.

Aloe polyphylla is a species displaying a perfect spiral pattern of its succulent leaves

Terrestrial members of the bromeliad family also sport fleshy leaves lined with vicious spines. Despite an

appearance similar to agaves, they are not related.

Dudleya brittonii from Baja California is a leaf succulent with a dense rosette of leaves covered in chalky white

wax granules to reflect away excess light and heat

Sedum laxum is a leaf succulent with red-tinted leaves adapted to heavy exposure to uv light in the high

mountains

Acacia craspedocarpa and many other Australian species of acacia have modified their leaf petioles into

flattened blades that serve as leaves.

Acacia longifolia phyllodes

Acacias start life off as seedlings with the more ordinary pinnately compound, fernlike leaves typical of

other members of the genus but quickly go over to making phyllodes as seen here

Insectivorous plants like Darlingtonia californica live in bogs where nitrogen is scarce. In order to make up for

this lack, they trap insects and digest them.

Here is a single Darlingtonia leaf, which lures insects inside by a combination of shape, color, and nectar,

where they fall to their death and drown

Aquatic leaves like the yellow pond lily (Nuphar lutea) have floating leaves attached to long stalks and anchored in the mud by roots. Inside the petioles are air chamber to pipe oxygen to

the roots.

Many plants such as some rushes and the restios from South Africa reduce leaves to non-green scales and

substitute their stems for photosynthesis. Stems have a smaller surface to volume ratio