This relates to the level within the hierarchy of plant names. The series of taxa for botany are set out in the International Code of Nomenclature for algae, fungi, and plants. Not all plants have an entry for every taxa and above the level of genus there is often a great degree of disagreement as to what belongs where. The important thing is that any plant can be identified by its genus and below.

 

Taxonomic rank

Kingdom

Subkingdom

Division

Subdivision

Class

Subclass

Superorder

Order

Suborder

Family

Subfamily

Tribe

Subtribe

Genus

Subgenus

Section

Subsection

Series

Subseries

Species

Subspecies

Variety

Subvariety

Form

Subform

(The principal taxa or in bold)