Here is a quick guide to the four domesticated species of Capsicum.

C. annum
Meaning "annual," which is an incorrect description. Capsicum annum is the most extensively cultivated throughout the world and because it cross pollinates so easily there are probably thousands of varieties existing. Annums are really divided into two catagories: sweet (or mild) and hot, which are referred to as Chillies. Many leaf variations but flower corollas are white with no spots.

C. baccatum
Meaning "berrylike". Capsicum baccatum plants are tall up to five foot with large dark green leaves. This species is distinguished from the other species by the flower corollas being white with distinctive dark green or brown spots, and anthers being yellow or tan. Fruity flavour being used in salsas or dried and ground into powders. The chillies known as Ajís make up this family. Can cross pollinate with C. annum.

C. frutescens
Meaning "shrubby or bushy". The most recognizable Capsicum frutescens is the Tabasco. These types of chillies are known as bird peppers in Asia. Bushy type of plant growing to 4 feet, with smooth oval leaves up to 7cm. Flowers have greenish white corollas with no spots and blue anthers, erect pods up to 4 cm long. Makes good pot plants. Freely cross pollinates with C. annum.

Capsicum chinense is now an obsolete designation as botanists now categorise them all as Capsicum frutescens. Growing from 1 to 5 feet high with pale to medium green large and wrinkled leaves. Flowers have white to greenish corollas and purple anthers and filaments. Slow growers with a long season. Most countries have their own name for the chinense: Habanero (Yucatán); Congo Pepper (Trinidad); Goat pepper (Bahamas); Scotch Bonnet (Jamaica).

C. pubescens
Meaning "hairy". The common name for Capsicum pubescens is Manzano (Mexico) or Rocoto (South America). Sprawling plant up to 4 feet high and two foot wide with oval light to dark green leaves being up to 8 cm long and very hairy. Flowers have purple corollas, purple anthers and stand erect above the leaves. Hardy plants with a long growing season. Will tolerate shade and light frost. As the pods are so fleshy they are usually eaten fresh in salsas or stuffed but they are very hot.  Does not cross pollinate with other Capsicum species. Is also claimed to be self-incompatible, so needs two or more plants to fruit.

Telling the Species Apart
The different types can be distinguished relatively easily by examining the flowers and seeds.

1. If it has black seeds and violet corolla then it is C. pubescens. If it has light coloured seeds, go to next step.
2. If the corolla has patches of colour it is C. baccatum. Otherwise go to next step.
3. If the corolla is greenish then C. frutescens. (Flowers in groups of two or more at each node previously known as C. chinense.) Otherwise go to next step.
4. If it has solitary flowers and stamina not violet it is C. annuum. Otherwise it is also C. frutescens (previously C. chinense)

Further Information
www.thechileman.org - Includes seed saving details and a database of over 3000 varieties with species names.