Leaf Shapes and Arrangements

Picture of Leaf Shapes

A tree's leaf is one major marker that helps in keying out and identifying any species of tree. Most trees can be identified by the leaf alone.

As you can see in the illustration, leaves come in many shapes and sizes. The "star" shape of sweetgum is totally different from the heart-shaped leaf of an eastern redbud. Note that leaves can be described by observing their base, their margin and their tip or apex. Each characteristic has a name and is used a part of the identification process.

Also a leaf can either be simple (no extra leaflets) or compound (three or more leaflets). On a compound leaf, all leaflets are attached to a single leafstem or rachis.

Leaf Tips: These can be rounded, pointed, or take on other forms.

• Attenuate: a sharp-pointed apex with concave margins that form an angle less than (<) 45 degrees.
• Acuminate: a sharp-pointed apex with straight or convex margins that form an angle less than (<) 45 degrees.
• Acute: an pointed apex with margins that form an angle between 45 and 90 degrees.
• Obtuse: a blunt apex with margins that form an angle greater than (>) 90 degrees.
• Rounded: an curved apex with margins that form a smooth arc.

• Caudate: an attenuate apex with a slender tail-like appendage at the tip.
• Cuspidate: an acute apex with a stiff tip or cusp.
• Mucronate: with a small extension of the midrib barely extending beyond the blade apex.
• Emarginate: with a shallow depression at the apex, not exceeding ? of the distance to the centre of the leaf blade

• Truncate: a broad, flat apex, abruptly ending at right angles to the midvein.
• Retuse: a rounded summit with a shallow depression at the apex, not exceeding 1/16 of the distance to the centre of the leaf blade.
• Obcordate: apex with prominent, rounded lobes, cut ? to ¼ of the distance to the centre of the leaf blade.
• Cleft: apex divided into rounded or straight-margined lobes, cut ¼ to ½ of the distance to the centre of the leaf blade.