| Name | Structure/ Category | Description |
|---|---|---|
| Oblong | (1) [Leaflets, Leaves, Petals, Phyllaries, Sepals] {shape} | Shaped like a compressed oval, with the sides approximately parallel for most of their length. (Compare with elliptic.) |
| Oblong | (2) [Buds] {shape} , [Seed cones] {shape before opening, shape when open} | Shaped like an elongated ellipsoid, the sides almost parallel from near one end to near the other end. |
| Oblong-cylindric | [Seed cones] {shape before opening, shape when open} | Intermediate in shape between oblong and cylindric. |
| Oblong-ovoid | [Buds] {shape} , [Seed cones] {shape before opening, shape when open} | Intermediate in shape between oblong and ovoid. |
| Obovate | [Leaflets, Leaves, Petals, Phyllaries, Sepals] {shape} | Egg-shaped with the point of attachment at the narrower end; inversely ovate. |
| Obovoid | [Seed cones] {shape before opening, shape when open} | Egg-shaped with the base at the narrow end; inversely ovoid. |
| Obtuse | (1) [Leaf apices, Leaflet apices, Petal apices, Phyllary apices, Sepal apices] {shape} | More or less blunt at the apex, with the sides coming together at an angle of greater than 90. |
| Obtuse | (2) [Leaf bases, Leaflet bases] {shape} | More or less blunt at the base, with the sides coming together at an angle of greater than 90. |
| Ocellated | [Leaf lower surface, Leaf upper surface] {color variegation} | A broad spot of some color has another spot of a different color within it. |
| Ocrea | a tubular sheath around the base of the petiole consisting of a single stipule in the red clover or a pair of coherent stipules in the buckwheat family (Polygoniaceae) |
