LEAVES

FOLIAGE

The leaves of a plant act like solar panels collecting the suns light to produce energy. Factors in the plants environment, like sunlight intensity, rainfall, wind, temperature, & herbivory shape the leaf. The foliage of a plant is where most of the respiration (plant breathing) takes place, through stomata.

LEAF MARGINS

The edge of the leaf is known as the leaf margin. This edge can be smooth, serrated, & deeply lobbed. Leaf margins are useful in identifying plants.

LEAF SHAPE

SIMPLE

Simple leaves are made up of a single, unbranched or unlobed leaf blade. Simple leaves have a single mid-rib. This leaf shape is effective in collecting large amounts of sunlight. The high surface area of this type of leaf results in increased water loss.

COMPOUND

Compound leaves are made up of multiple Leaflets. These leaflets are attached to the mid-rib, & in the case of double pinnate leafs the leaflets are attached to the secondary leaf ribs. Compound leaves in this arrangement are referred to as Pinnate. Some compound leaves are attached to a single mid-rib in a fan/hand like shape. Compound leaves in this arrangement are referred to as Palmate.

ADAPTATIONS TO LIGHT INTENSITY

In general, the less sunlight in the environment the larger the plants leafs. The color & texture of the leaf surface affects the amount of sunlight absorbed by the plant. Desert plants often have silvery foliage (some even have crystals) that reflects intense sunlight. Some plants have hairs on the leaf surface to shade & insulate. Other plants have thick waxy leaf surfaces (cuticles) to protect them from sun burn.

FOLIAGE ADAPTATIONS TO TEMPERATURE

Plants from cold climates practice the same strategies as those from dry hot areas: small tightly packed foliage, thick waxy cuticles, & insulating hairs. Many plants from cold climates have small, scale like densely packed foliage. Other plants have lost their foliage completely (cacti), others only drop them in extreme weather (deciduous plants). Plant foliage from hot humid areas is often waxy & waterproof.

FOLIAGE ADAPTATIONS TO RAINFALL

Water is probably the most important resource for plant growth. The amount of available moisture in the plants environment has a great effect on the shape & other physical characteristics of the leaf. Plant leafs have to evolve to store water in areas where it is scarce & also to shed water of the foliage where it is abundant. Many plants lose their foliage (deciduousness) during drought. Some plants even have two different types of leafs for wet weather & dry weather (dimorphic foliage).

FOLIAGE ADAPTATIONS TO HERBIVORY

Plants are the base of the food chain & are frequently on the menu. One of the simplest strategies plants use are spines, thorns, or prickles. Because of herbivores plants have developed foliage that is poisonous or foul tasting. Some plants are poisonous even to touch, causing skin, eye, & nose irritation.

FOLIAGE ADAPTATIONS TO POOR NUTRIENT ENVIRONMENTS

Some plants come from environments that are poor in nutrients (Ogliotrophic). These plants have evolved specialized strategies to capture nutrients. Bromeliads growing on tree branches & rocks grow in no soil. Their leaves funnel water & nutrients into a cup where the plant can absorb them. The leafs of carnivorous plants have evolved into elaborate traps.

LEAF ARRAGEMENT

ALTERNATE

In the Alternate leaf arrangement there is one leaf per node. The leafs alternate up the stem in a spiral. The leafs always have stem (no leafs or nodes) opposite of them.

OPPOSITE

In an Opposite leaf arrangement there is one leaf per node. Each leaf has another leaf & node opposite to it. These leafs occur in pairs (more than two is a Whorled flower).

WHORLED

In a Whorled leaf arrangement there is simply three or more evenly spaced leaves per node. These leafs are usually spiraled around the foliage. Tightly packed whorls are known as Rosettes.

BASAL

In a Basal Leaf Arrangement a dense cluster of leaves radiate out in a spiral at or near ground level. Buds & apical meristems are packed together in between the foliage.