ob-: Greek prefix, meaning in a reverse direction.

obcordate (1 image): like cordate, but with the notch at the tip.

obdiplostemonous: with 2 cycles of stamens.

oblique: slanting, or sloping at an angle.

obsolete: so much reduced as to be scarcely detectable or entirely suppressed.

obtuse: blunt; with the sides coming together at an angle of more than 90 degrees.

ocrea (15 images): a sheath around the stem just above the base of the leaf, derived from stipules.

ochroleucous (3 images): yellowish-white.

offset: a short, prostrate shoot, primarily propagative in function.

operculate: provided with an operculum.

operculum: a little lid; the deciduous cap lid of a circumscissile fruit or other organ.

opposite (29 images): situated directly across from each other at the same node; situated directly in front of (on the same radial line as) another organ, as stamens opposite the petals.

orbicular: circular in outline.

orthotropous ovule: one that is straight or unbent.

oval: broadly elliptic.

ovary (1 image): the structure that encloses the ovules of angiosperms; the expanded basal part of a pistil, containing the ovules.

ovate (6 images): egg-shaped in outline.

ovoid: shaped like an egg (applied to solid objects).

ovule: a young or undeveloped seed.