The scientific name of a species is formed by the combination of two terms The first name (capitalized) is the genus of the organism, the second (not capitalized) is its species.

How to Write the Scientific Name of a plant:
There are precise convention to follow when writing a scientific name.
Genus Name

1. The genus name is written first.

2.  The genus name is always underlined or italicized.

3.  The first letter of the genus name is always capitalized

Example: Astrophytum or Astrophytum

Specific name

1. The specific epithet is written second.
2. The specific epithet is always underlined or italicized.
3. The first letter of the specific epithet name is never capitalized.

Example: myriostigma or myriostigma

Scientific Name - The scientific name of this plant would appear as follows:

Astrophytum myriostigma or Astrophytum myriostigma

Mutations? Frequently a particular individual of a species will mutate to a diverse colour, size, or growth habit. These characteristics are passed on to its descendants (offsprings). When this happens, a population of plants exists with the same scientific name, but a sub-group displays different characteristics. If the mutated group is significantly different from the parents and is stable (the traits are passed on from generation to generation), then this new group of plants is often assigned a variety name.

Variety Names
A.     Variety names are given when the mutation occurs in nature. (E.g. a mutation occurs in a wild arid land)
B.     The abbreviation var. is used to signify that the mutation is a variety. var. is placed after the specific epithet and is not underlined or italicized.

           Example: Astrophytum myriostigma var.

1.     The variety name is written after var.
2.     Capitalize the first letter of the variety name only if it is a proper noun. (e.g. Pediocactus peeblesianus var. Menzelii)
3.     Underline or italicize the variety name.

Example: Astrophytum myriostigma var. strongylogonum  or Astrophytum myriostigma var. strongylogonum

Form (forma) Names
A.     Form names are given for sporadic or minor variations occurring among individuals of any population,  mainly in horticultural applications ((E.g. a mutation in spine length or  flower colour)
B.     The abbreviation f. is used to signify that the mutation is a form. forma (f.)  is placed after the specific epithet and is not underlined or italicized.

           Example: Astrophytum myriostigma f..

1.     The form name is written after forma (f.).
2.     do not capitalize the first letter  (e.g. Astrophytum myriostigma f.. quadricostata)
3.     Underline or italicize the form name.

Example: Astrophytum myriostigma forma quadricostata  or Astrophytum myriostigma f. quadricostata
 

Mutations can also take place because of human involvement such as breeding, applying mutagens, propagation, or by cultural practices. In these cases, the new group of mutated plants is called a cultivar. "Cultivar" is an abbreviated form of cultivated variety. The mutated plants are assigned a cultivar name.

Cultivar Names
A.     Cultivar names are given when the mutation occurs due to human influence.
Example: a mutation occurs in a green house.
B.     The abbreviation cv. is used to signify that the mutation is a cultivar. cv. is placed after the specific epithet and is not underlined or italicized.

Example: Astrophytum myriostigma cv. Onzuka.
or single quotes are used instead of cv.
Example: Astrophytum myriostigma  'Onzuka'

1. The cultivar name is written after cv. or within the single quotes.
2. Capitalize the cultivar name.
3. Never underline or italicize the cultivar name.

Example: Astrophytum myriostigma cv. Onzuka. or Astrophytum myriostigma  ‘Onzuka'

Also after a taxonomic revision that results in a species being reclassified in another genus, the specific epithet must remain the same as the one in the basionym. For instance the cactus  Eriosyce napina  (current name attributed by Kattermann in 1994) was formerly classified by Philippi in 1872 as  Echinocactus napinus (basionym).
When a species name changes, to show the connection to the source of the new name, botanists retain the name of the basionym author by placing it in parentheses, the authority of the new combination is placed after the parentheses (e.g. Eriosyce napina (Philippi) Kattermann 1994).