A "parent plant" in the sense of the pharmaceutical definition is a defined plant species from which a pharmaceutical drug is produced by means of different processes and preparations.
The parent plant is named according to its biological nomenclature (botanical name, including author's abbreviation, e.g. L. for Linné).
The parent plant indicates the origin of a herbal drug. The drug is usually only extracted from a specific part of the plant (flowers, roots, rhizomes, above-ground herb, etc.). It is prepared by different, standardised procedures.
For example, "Panax ginseng C.A. Meyer", the ginseng plant named after C.A. Meyer, is the parent plant of Ginseng Radix, the official ginseng root monographed by Commission E, also known as Panax root. For this drug, only the dried roots of the ginseng plant, obtained by steam distillation, are used and not the whole plant (parent plant).
Lavendula angustifoliae Mill, the lavender plant, is the parent plant of Lavendulae flos also known as Flores Lavendulae, the officinal drug "lavender flowers" defined by various monographs. This drug is extracted exclusively from the fresh, not yet blooming flowers of the lavender plant.
In Quercus cortex of the official by various monographs. There are several parent plants (Quercus rubor L. (L. stands for the author Linné), Quercus petraeae, Quercus pubescens) whose cut and dried bark as well as their fresh young branches are processed together to the drug "Quercus cortex".