Ob- - A prefix that indicates reversal of the usual orientation. (e.g. oblanceolate means widening gradually from the pointed base to a maximum near the apex, which may be more or less rounded).
Oblong - Longer than wide and rounded at the ends, with nearly parallel sides for much of the length.
Obtuse - Rounded or blunt.
Opposite - Growing two to a node on opposite sides.
Orbicular - circular or approximately round.
Oval - Broadly elliptical.
Ovate - Shaped like an egg, with the narrow end at the apex.
Ovoid - Ovate.
Palmate - Compounded, divided, lobed, or ribbed so that the divisions or ribs spread out like fingers from a single point.
Panicle - A raceme compounded by branching.
Papolionaceous - Descriptive of a flower whose petals are arranged to resemble a butterfly.
Pedicel - The stalk of one flower in a cluster.
Peduncle - The stalk of a flower cluster or of a solitary flower.
Peltate - Having a stalk attached at or near the middle.
Perennial - Living through three or more seasons.
Persistant - Remaining on the plant; not falling off readily.
Petal - One unit of a corolla.
Petiole - The stalk of a leaf.
Pinna - (plural pinnae) - A leaflet or primary division o a pinnately compound leaf.
Pinnate - Having leaflets arranged in opposite rows along the petiole.
Pinnatifid - Split about halfway to the mid-rib, such that the divisions are pinnately arranged.
Pinnule - One of the divisions of a pinnate leaflet in a bi-pinnate leaf.
Pistil - The female reproduction organ of a flower.
Pod - Generally, a dry fruit that splits open.
Pome - A fleshy fruit with a central seed-bearing core. (e.g. apple).
Procumbent - Growing along the ground without rooting, and having ascending tips.
Prostrate - Growing flat along the ground.
Pubescent - Covered with down or soft, short hairs.
Punctate - Having translucent spots or depressions.