Chillies - Taxonomy and Heat rating

Capsicum annuum is a domesticated species of the plant genus Capsicum native to southern North America and northern South America.
The genus Capsicum is in the family Solanaceae in the major group Angiosperms (Flowering plants).

There is much debate surrounding the designation of Species contained within the Capsicum genus. It is commonly accepted that the genus Capsicum consists of five domesticated species and twenty-six wild species.


Domesticated species
·  Capsicum annuum
·  Capsicum baccatum
·  Capsicum chinense
·  Capsicum frutescens
·  Capsicum pubescens


The Chileman website provides a detailed listing and description of the species and their characteristics:  Chileman.org species list

Formal Classification
Kingdom:         Plantae
Subkingdom:   Tracheobionta
Division:          Magnoliophyta
Class:              Magnoliopsida
Subclass:        Asteridae
Order:              Solanales
Family:            Solanaceae
Genus:            Capsicum

Classification is a vast topic which I cannot begin to cover in sufficient detail here,
however a good starting point would be the various pages on Wikipedia:
http://en.wikipedia.org/wiki/Plant_taxonomy
I would also recommend a visit to the RHS website:
http://apps.rhs.org.uk/rhsplantfinder/plantnaming/
.
Although the species name annuum means “annual” (from the Latin annus “year”),
the plant is not an annual and in the absence of winter frosts can survive several seasons and grow into a large perennial shrub.
The single flowers are an off-white (sometimes purplish) color whilst the stem is densely branched and up to 60 centimetres (24 in) tall. The fruit is berry which may be green, yellow or red when ripe.Whilst the species can tolerate most climates, C. annuum is especially productive in warm and dry climates.


The Scoville scale is a measurement of the spicy heat (or piquance) of a chili pepper.
The number of Scoville heat units (SHU) indicates the amount of capsaicin present. 

Capsaicin is a chemical compound that stimulates chemoreceptor nerve endings in the skin, especially the mucous membranes.

The scale is named after its creator, American pharmacist Wilbur Scoville. His method, devised in 1912, is known as the Scoville Organoleptic Test. The modern commonplace method for quantitative analysis uses high-performance liquid chromatography, making it possible to directly measure capsaicinoid content.