Obcordate
Inversely cordate; heart shaped; if it is a leaf apex, the petiole attaches at the narrow end.
Oblanceolate
Inversely lanceolate; Much longer than wide with the widest point above the middle. Narrower than obovate (See also Lanceolate).
Oblique
Unequal or asymmetric especially in leaf-blade or leaf base.
Oblong
Two to four times longer than wide with nearly parallel sides.
Obovate
Inversely ovate or teardrop-shaped; leaf connected to petiole at narrow end. Wider than oblanceolate (See also Ovate).
Obtuse
Rounded leaf apex, greater than 90º at apex.
Odd-pinnate
A pinnately compound leaf that ends in a single leaflet so that there is an odd number of leaflets (See also Even-pinnate and Pinnate).
Opposite
Appear across from one another at the same node; opposite leaves may also appear decussate (each pair alternating at 90º angles at every node).
Orbicular
Circular or rounded in leaf.
Oval
Two times longer than wide with rounded ends.
Ovary
The lower portion of the female pistil that contains the ovules (See also Stygma and Style).
Ovate
Teardrop-shaped in outline and attached (to petiole) at the broad end; Wider than Lanceolate.
Ovoid
A three dimensional part that appears egg-shaped; buds, fruits, etc.