Botanical Identification of St. John's Wort (Agrimonia eupatoria)

To identify St. John's Wort (Agrimonia eupatoria) accurately, examine its morphological characteristics, taxonomic classification, and diagnostic features.

St. John'S Wort (Agrimonia eupatoria) Monograph

Scientific Classification

St. John's Wort, or Agrimonia eupatoria, belongs to the plant kingdom, specifically within the flowering plants. It is classified under the eudicots, part of the Rosales order, and the Rosaceae family. The genus Agrimonia includes this species, which is known for its medicinal properties.

The following table shows the full taxonomy of this plant.

Botanical Nomenclature and Synonyms

The scientific name of St. John's Wort is Agrimonia eupatoria, first described by Carl von Linné in 1753. It has several synonyms, including Hypericum perforatum, though this refers to a different species. Common names include St. John's Wort, Mary's Wort, and others, while regional and historical names vary across cultures and time periods.

Morphological Characteristics

St. John's Wort (Agrimonia eupatoria) is a herbaceous perennial with a sprawling growth habit. It has a fibrous root system and branching stems that often lie on the ground. Its leaves are pinnately compound with serrated leaflets. The inflorescence is a dense, terminal cluster of small yellow flowers. The fruit is a capsule containing small, flat seeds.

Diagnostic Identification Features

St. John's Wort can be distinguished by its distinctive yellow flowers with five petals, bright red stamens, and five green sepals. It has opposite, pinnately compound leaves with serrated edges. The plant typically grows 30-100 cm tall, with a sprawling habit and hairy stems. It is often found in dry grasslands and along roadsides.

Natural Habitat and Geographic Distribution

St. John's Wort (Agrimonia eupatoria) is native to Europe, western Asia, and northern Africa. It thrives in temperate climates with full sun. It prefers well-drained, sandy or loamy soils. It typically grows between 200 and 1,500 meters above sea level.

Phenology and Growth Cycle

St. John's Wort blooms from June to August, producing bright yellow flowers with orange stamens. Seed formation occurs in late summer, typically from August to September. For identification, the plant is most easily recognized during its flowering stage, which is ideal for accurate botanical identification.

Phylogenetic Relationships

St. John's Wort, Agrimonia eupatoria, is closely related to other members of the Rosaceae family. It shares characteristics with species like Agrimonia sphaerocephala and is part of the genus Agrimonia, which includes several similar plants with similar morphological and ecological traits. Its phylogenetic placement reflects its evolutionary ties to other rose family members.