The Leaf
“Oh leaf, you must surely have found strength to force the branch to burst open so that you could emerge. What did you do to become free from the prison? Speak, Speak…” -Rumi
A leaf is like a flag unfurling. The emerging leaf from the stem announces the beginning of the metamorphosis from stem to flower, from winter to spring. It is the opening up of the new leaf that announces new life. Humans and animals begin to notice a plant once the leaf emerges. It is our food and it is our hope for spring and the first harvest. Leaves provide brilliance in the spring and shade in the summer. They are perfect food containers and provide food for many species on the earth. Later when the seasons turn to winter, the leaves that have fallen on the ground provide protection and fertilizer to the creatures of the forest and other environments. Leaves provide more than half the human food needs. Another large portion of leaves are used for the feeding of livestock. Without leaves, humans would starve or die from malnutrition.
THE PRIMORDIAL LEAF
When last I wrote I told you about the mersistem cells and the apical cap or bud that is growing up toward the light. 
It is also, at precise intervals, creating appendages that will become branches and possibly leaves. The apical bud is involved in making the stem growing longer, initiates the orderly arrangements of leaves on the stem, and makes provision for the eventual development of branches. This early period of leaf production in the mersistem bud is called leaf primordia. A primordium, the nascent leaf, forms at the least crowded part of the shoot meristem. The leaf cells fold over the meristem bud to protect it from sun and other weather. At just the right time, when the days are longer and the air temperature is warmer, the leaf begins to grow larger and then finally opens up. At the base of the leaf primordia a bulge appears and it is called “axillary bud primordium” and is the beginning of a branch. A branch forms at the axil or angle between the leaf and the stem.
Now the meristem cells are following the DNA blueprint of this plant whether it will be at maturity a tree or a sunflower. And as the meristem cells formulate the stem it is remembering the specific design and pattern of this plant. It “remembers” at what interval to place the leaf nodes or the branch nodes. The branch node of course can grow leaves as it extends its growth.
The cellular structure of the leaf is all about meristem cells, stomata, glucose storage and photosynthesis. In review, the stomata’s main function is to allow gases such as carbon dioxide, water vapor and oxygen to move rapidly into and out of the leaf. Stomata are found on all above-ground parts of the plant including the petals of flowers, petioles, soft herbaceous stems and leaves.
Leaf Stomata
Stomata are the main “food manufacturing” organs of the leaves. They make food from carbon dioxide and water in the presence of light during a process called photosynthesis. As stomata open in the presence of light, carbon dioxide will diffuse into the leaf as it is converted to sugars through photosynthesis inside the leaf. At the same time, water vapor will exit the leaf along a diffusive gradient through the stomata to the surrounding atmosphere through the process of transpiration.
Another very interesting thing happens at the point that the meristem cells decide to create a leaf. The cells start to create new chemicals. One such chemical is chlorophyll. And, cell tissue that is filled will chlorophyll will turn green. Leaves receive their green color during the process of trying to absorb energy from the sun. The sunlight strikes the leaves, which contain chlorophyll, and the chlorophyll reacts by emitting the green color. Likewise in the autumn some plant leaves turn color because as the days shorten and leaves absorb less light, the leaves prepare for autumn by stopping the food-making process. Consequently, the production of chlorophyll drops off, turning some leaves orange and yellow in the fall.
Colors, like yellow and orange, are in leaves all summer, but the powerful green chlorophyll overwhelms them. Once the cold shorten days come on in the fall, chlorophyll disappears and the leaf’s other colors shine through.
THE PATTERN IS THE KEY
Each plant has a pattern for growing stems, branches and leaves.
- A leaf is connected to the stem by a structure called the petiole.
▫ The base of the stem where the petiole connects is called the node
▫ Where the petiole connects to the leaf is called the axil
▫ The axil is where we happen to find buds, clusters, and emerging leaves.
Leaves appear on the stem in a set pattern. Learning the leaf patterns will help you identify the plant and help you use plant keys
Leaf Morphology: Shape and arrangement, margin and venation
Studying the different shapes and designs of the leaf will also help you to identify a plant. Each plant has a pattern of growth. Identifying the overall shape of the leaf, the outer edge of the leaf (margin) and the pattern of leaf veins will help you to identify or key the plant type. Developing a keen eye for observation will help. I actually draw the leaf so I can more fully study it.
Overall Shape of the leaf
Many plants have adapted leaf shapes that help water drip off the plant to avoid too much moisture, which might make bacteria and fungus grow. The leaf shape and arrangement on the stem will funnel water to the root. The leaf shape may provide a platform to collect the sun’s rays or keep wind from blowing the plant apart.
Arrangement of the leaf on the stem
Leaf arrangement types on the stem
In botany the word “phyllotaxis” is a word used to describe the study of the arrangement of the leaf on a plant stem. . There are four primary leaf arrangements: Alternate, opposite, whorled and rosulate. (Please see illustration).
- Opposite leaves are positioned across the stem from each other, with two leaves at each node.
- Alternate (spiral) leaves are arranged in alternate steps along the stem, with only one leaf at each node.
Whorled leaves are arranged in circles along the stem.
Rosulate leaves are arranged in a rosette around a stem with extremely short nodes.
Leaf Margins
Leaf Morphology Chart
The leaf margin is the outer edge of a leaf. There are many different margins. Here is a list of margin types listed on Wikipedia . Learning these types of margins will help you to key a plant. (Please see illustration on left. CLICK TO ENLARGE -also found on Wikipedia -thank you Wikipedia!).
- ciliate: fringed with hairs
- crenate: wavy-toothed; dentate with rounded teeth, such as Fagus (beech)
- crenulate finely or shallowly crenate
- dentate: toothed, such as Castanea(chestnut)
- coarse-toothed: with large teeth
- glandular toothed: with teeth that bear glands.
- denticulate: finely toothed
- doubly toothed: each tooth bearing smaller teeth, such as Ulmus (elm)
- entire: even; with a smooth margin; without toothing
- lobate: indented, with the indentations not reaching to the center, such as many Quercus(oaks)
- palmately lobed: indented with the indentations reaching to the center, such as Humulus (hop).
- serrate: saw-toothed with asymmetrical teeth pointing forward, such as Urtica (nettle)
- serrulate: finely serrate
- sinuate: with deep, wave-like indentations; coarsely crenate, such as many Rumex (docks)
- spiny or pungent: with stiff, sharp points, such as some Ilex (hollies) and Cirsium (thistles).
Design of the veins found on the leaf
There are two subtypes of venation, namely, craspedodromous, where the major veins stretch up to the margin of the leaf, and camptodromous, when major veins extend close to the margin, but bend before they intersect with the margin.
- Feather-veined, reticulate arise from a single mid-vein and subdivide into veinlets. These, in turn, form a complicated network. This type of venation is typical for (but by no means limited to) dicotyledons.
- Palmate-netted or fan-veined; several main veins diverge from near the leaf base where the petiole attaches, and radiate toward the edge of the leaf, e.g. most Acer (maples).
- Parallel-veined or parallel-ribbed– veins run parallel for the length of the leaf, from the base to the apex. Commissural veins (small veins) connect the major parallel veins. Typical for most monocotyledons, such as grasses.
- Dichotomous – There are no dominant bundles, with the veins forking regularly by pairs; found in Ginkgo and some pteridophytes.
For a full discourse on every leaf shape possible check out Wikipedia http://en.wikipedia.org/wiki/Leaf_shape
LEAVES FOR FOOD AND MEDICINE
For as long as humans have been on the earth, the leaves of plants have been used for food, medicine, shelter and utility. Green has been a sacred color to those cultures who understood the important relationship between humans and plants. Leaves were used in ceremony, clothing and decoration.
Children learned rhymes and axioms that taught them to identify the helpful and not so helpful plants around them. Here are just a few:
- The leaves of three, Leave it be. The leaves of four have some more. (a song to teach a child to identify Poison oak or Ivy)
- Hairy vine? No friend of mine!
- Berries white, danger in sight!
- Red leaflets in spring are a dangerous thing.
- Side leaflets like mittens will itch like the dickens!
- Berries of red will soon be dead!
- Berries of black, caution for that. Or ”Berries of black, ask about that.”
Nutrition of plant leaves
Humans have been able to survive the long months to the first harvest by storing food and by harvesting early spring plants. Roots are important through the winter months. But the early green leaves of Stinging Nettles (Urtica dioica), Miners lettuce (Claytonia perfoliata), Dock (Rumex patientia L,) Dandelion (Taraxacum) and hundreds of other species have allowed humans to survive until the next great harvest.
Nutritional – Medicinal
There were a number of plants that were known by the First Peoples of Cascadia that helped humans survive starvation and nutritional imbalance. Known by Europeans as “Spring tonic” plants, these plants with their new shoots are full of nutrients that are helpful to our well being. For instance- Stinging Nettle (Urtica dioica) when picked young, can be steamed and eaten in February and March. This plant has been known to alleviate muscle pain, depression and tiredness. It truly is a spring tonic. Stinging Nettle is often found in semi-wet well drained areas.
Stinging Nettle (Urtica dioica) and the Spring Potherb
Stinging Nettle (Urtica diocia)
Stinging Nettle is a herbaceous perennial flowering plant, native to Europe, Asia, northern Africa, and North America,and is the best-known member of the nettle genus Urtica. It was a survival plant for First Peoples and others who moved here to live. It is a key ingredient in the Spring Potherb. This is a soup where early plants are steamed and cooked into a broth and drunk to get one’s body ready for spring and summer. It wakes up the body, mind and spirit. The greens are also consumed. The greens contain vitamin C, iron and many minerals.
Recipe for the Spring Potherb
Bring a big pot of water to boil, turn down the heat. Place plants into the water and turn off heat. Season to taste.
Stinging Nettle
Chickweed
Clover
Dandelion leaf and root
Great Burdock
Lamb’s Quarters
The fresh leaves of Stinging Nettle contain vitamins A, C, D, E, F, K, P, and b-complexesas well as thiamin, riboflavin, niacin, and vitamin B-6, all of which were found in high levels, and act as antioxidants. The leaves are also noted for their particularly high content of the metals selenium, zinc, iron, and magnesium. They contain boron, sodium, iodine, chromium, copper, and sulfur.
Stinging Nettle is a versatile plant. The plant is not only eaten, but as the plant matures the fibers of the plant were used for making many useful things. The fibers have been used for thousands of years for shoes, hats, fabric for clothes, fishing line, and was woven into twine and rope. The use of Nettle fiber worldwide is the similar to the use of Hemp or Flax. Used to weave fabric of all kinds, it is has also been used to press into paper. The nettle fiber is usually mixed with other paper-making plants as it does not possess the gluey substance needed to allow the paper fabric to hold together.
The Sting of the nettle is said to be a cure for Arthritis and other diseases of muscles, joints, and some organ tissues.
The antidote for being stung by this plant is the juice found inside the stem or Dock (Rumex patientia) which usually grows nearby. A Plantain (plantago macrocarpa) or (plantago lanceolata) poultice can also be used as antidote for the sting.
NEVER COLLECT THESE PLANTS ALONG POLLUTED WATERWAYS, ROADS OR INDUSTRIAL AREAS. This plant, as well as all plants, is adapted to uptake dangerous heavy metals (bio-remedial). Always harvest in safe areas.
“Nature will bear the closest inspection. She invites us to lay our eye level with her smallest leaf, and take an insect view of its plain.” – Henry David Thoreau
Vocabulary
Axillary bud primordium – An immature axillary bud. An embryonic side shoot. A point on a stem, at the node, and between the stem and leaf, where a new shoot can develop. Growth is usually inhibited at these buds.
Leaf primordia – A lateral outgrowth from the apical meristem that develops into a leaf
Petiole – The stalk that joins a leaf to a stem; leafstalk
Photosynthesis – The process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a byproduct.
Transpiration – the emission of water vapor from the leaves of plants. Water loss that occurs through the open plant stomata (tiny pores primarily on the underside of the leaf). Rate of loss is determined by wind and atmospheric humidity conditions.
References
- Capon, Brian (1990) (Revised 3rd edition, 2005) Botany for Gardeners, Timber Press, Portland, London
- Gunther, Erna. (1945) (Revised 1973) Ethnobotany of Western Washington. Knowledge and use of Indigenous plants by Native Americans, University of Washington Press.
- Pojar & McKinnon, (1994) Plants of the Pacific Northwest Coast, Washington, Oregon, British Columbia & Alaska, Lone Pine Publishing, Vancouver, British Columbia
- Wikipedia – viewed on the internet April 2012.
NEXT TIME: THE FLOWER
Green Lady - Ellen
Radical Botany 