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

Bark texture, color, other features: bark smooth and light gray/brown

Leaf structure, shape, color, persistence, other features: leaves evergreen, 1-2 inches long by 0.5-1 inch wide, solitary, oblong with obtuse tip. Margins entire and revolute, new growth red.

Flower color, size, form, arrangement, blooming period, persistence, other features: 

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

Root features: No prominent surface roots

Key features for identification: Revolute margins on leaves, leaves thicker than other stopper species

Similar species/often confused with: 

Spanish stopper (Eugenia foetida)
Similar features: opposite simple leaves, overall size, multi-stemmed with thin branches, evergreen
Distinguished by: revolute margins on Simpson's stopper, Simpson's also has thicker leaves with a more glossy look/leathery feel, new growth distinctly red.

External links: 

Institute for Regional Conservation:
https://www.regionalconservation.org/beta/nfyn/plantdetail.asp?tx=Myrcfrag