leaves

In any field of study there is always a large vocabulary to learn. Botany is no different. Unfortunately for plant identification there are many, many new words to learn. I find it somewhat daunting, but lets start with some basics.

Plants are grouped in various families according to physical characteristics. We assume, though not always correctly, that the more similar the anatomy the more closely related the plant. To be able to identify a plant, we need to be able to recognize certain characteristics organs that they share with certain other plants. Organs include leaves, stems, roots, flowers, fruit and seeds.

The first thing we usually notice about a plant are its leaves. These are vegetative organs as opposed to reproductive organs. The shape, the way they are attached to the stem or stalk, their smoothness or hairiness, these all give clues to a plant's identity. There is a whole vocabulary to describe leaves. I will take you for a walk in my garden to illustrate some of the possibilities.

Simple leaves	Compound leaves - pinnate or palmate

Simple leaves are a single blade though they may come in many shapes and sizes and be deeply lobed.	Compound leaves are composed of 2 or more similar leaflets attached to a rachis (stem). They may be pinnate or palmate.
	Ferns provide good examples of pinnate leaves. In the pinnate Christmas fern (Polystichum acrostichoides) to the left, the pinnae are distinctly separate from the midvein or rachis. If the leaves are deeply divided (more than midway to the rachis) but not detached, they are called *pinnatifid. (Onoclea sensibilis). There are many more complex structures like the bipinnate pinnatifid leaf of our bulblet fern (Cystopteris bulbifera). Here the ranchis branch to form smaller midribs called* costa (or rachilla) and the pinnae attached to the costa are deeply cut but not entirely separated. Compound pinnate leaves can be quite complex as in the 2-4-ternately compound Caulophyllum thalictroides (the leaflets are present in groups of two to four on three branchlets). (ref Efloras)	Palmately compound leaves are composed of several leaflets radially diverging from the petiole like the spread of fingers. These can be unifoliate (apparently Citrus looks like a simple leaf but has modified leaflets at the base), bifoliate (as found in Hardwickia) and so on to the multifoliate plants like schefflera (left). Trifoliate leaves as in bogbean (Menyanthes trifoliata -shown right) are sited both as pinnate or palmate. Medicago and Melilotus are classified as pinnate as the central leaflet has a longer petiolule (stalk) - this does not appear to be the case of bogbean, but let me know your thoughts. (See Plant Systematics p 67)

*Alternate leaves* one leaf attached per node	*Opposite leaves* two leaves attached per node	*Whorled leaves* three or more leaves attached per node

The leaves are said to be *distichous* if they are arranged in two vertical rows on opposite sides of an axis. They may also be spiraled (Euphorbia myrsinites - right). Leaves may be fascicled ( 2 to 5 leaves bundled and held at the base by sheath, as in many pines) or clustered in false whorls (without a basal sheath).	If successive leaf pairs are perpendicular, this is called *decussate* as in the dogwood (Cornus stolonifera -right).	A basal whorl with a large number of leaves spread out in a circle is called a rosette.

Are their any special features - stipules or glands?

Stipules	Glands

Stipules are appendages attached to the base of the petiole. They often occur in pairs as in the pair of thin leaf-like stipules on this plum (Prunus domestica). When they are fused to the petiole, they are termed adnate, as the wing-like adnate stipule on this old rose (Rosa rugosa 'Blanc Double de Coubert'). A plant that has no stipules is said to be exstipulate.	Sometimes you will note small features like the protruding red glands on this cherry leaf (Prunus cerasus). Such glands can help distinguish between species.

What kind of veins does the leaf display?

Parallel	Pinnate	Palmate	Arcuate	Reticulate
Typical of monocotyledonous plants	There is one major vein and distinct side veins that branch off like the teeth of a comb	The large veins all start at the end of the petiole and extend through the blade like fingers	This is a pinnate leaf with veins that arc toward the apex.	Reticulate leaves have a network of veins and may be pinnate or palmate.

While these are the basics there are unusual combinations. See the rotating veins of European ginger photo below (see also the chart from Wiki on leaf morphology ).

How do you describe the leaf shape and leaf margin? Here are a few examples.

Hydrangea arborescens ovate, margins coarsely serrate	Ilex meserveae oval, margins spiny	Tulipa tarda linear, entire	Phlox stolonifera spatulate, entire	*Kerria japonica* deltoid, margins doubly serrated	*Allium schoenoprasum* tubular	*Iris germanica* enisform
Hydrangea petiolaris orbicular with serrated margin and acute apex	Stylophorum diphyllum deeply lobed; margins irregularly crenate	Asarum europaeum reniform, margins entire (note how the veins rotate)	*Picea abies* acicular, needles 4-angled in cross section, apex blunt	*Epimedium x rubrum* compound biternate to triternate, leaflets cordate and partially hastate, spiny teeth on margins	*Anemone acutiloba* leaf blade widely orbiculate, base cordate, margins entire, apex acute or acuminate; lobes 3, deltate (Efloras)	Thuja occidentalis appressed, scalelike, lateral pairs keeled, facial pairs flat (EFloras)

See also Britannica's leaf sphapes for visual reference.

This is just a brief look at some leaf types.

Check out some flowers

Plant anatomy http://hort201.tamu.edu/YouthAdventureProgram/PlantAnatomy/Anatomy.htm

Petiolate	Sessile	Perfoliate	Sheath

Leaves are attached to the stem with a simple stalk	The petiole is absent and the leaf is attached directly to stem	The stem passes through the leaf.	The leaf blade or petiole fits into a tube that surrounds the stem above the node