Mature size: 15-20 feet, taller than wide

Branch arrangement, structure, other features: opposite branching, typically multi-stemmed, branches very thin

Bark texture, color, other features: opposite branching, typically multi-stemmed, branches very thin, bark smooth and light gray to light brown

Leaf structure, shape, color, persistence, other features: leaves evergreen, 1-2 inches long by 0.5 inch wide, simple, evergreen, oblong with obtuse tip, new growth reddish. Margins entire though some leaves have some wavy/crenulate margins in isolated areas.

Flower color, size, form, arrangement, blooming period, persistence, other features: flowers white, somewhat showy, fragrant

Fruit size, color (early/ripe), form, persistence, time of year, other features:

Root features: roots not prominent

Key features for identification:

Similar species/often confused with:

spicewood (Calyptranthes pallens)
Similar features: opposite leaves, overall size, multi-stem with thin branches, evergreen, simple leaves
Distinguished by: spicewood leaves grow at near 90-degree angle to stem. Spicewood leaf margins are entire, Spanish stopper leaves have some waves/crenulation in isolated areas.

External links: 

Institute for Regional Conservation:
INSERT LINK