Hieracium lachenalii: A Comprehensive Profile of Common Hawkweed
Hieracium lachenalii, widely known by its English name, Common Hawkweed, is a resilient plant species belonging to the Asteraceae family (the daisy or sunflower family). While it is a native inhabitant of much of Europe, this adaptable species has expanded its reach, establishing itself as a common weed in parts of North America and Australia.
Understanding this plant requires a look into its complex botanical history and its distinctive physical characteristics. As a member of the tribe Cichorieae, it shares many traits with other members of its lineage, yet it maintains unique identifiers that set it apart in the field.
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Key Facts
- Scientific Name: Hieracium lachenalii
- Common Name: Common Hawkweed
- Family: Asteraceae
- Native Range: Most of Europe
- Invasive Status: Established in Australia and North America
- Flower Color: Pale yellow
- Growth Habit: 4 to 36 inches tall
Taxonomy and Naming History
The classification of Common Hawkweed has undergone significant revision due to modern botanical studies. For many years, the species was widely identified as H. vulgatum. However, researchers determined that H. lachenalii and H. vulgatum actually represent the same species.
In botanical nomenclature, priority is given to the oldest validly published name. Because the name Hieracium lachenalii was coined in 1802, while H. vulgatum was established in 1819, H. lachenalii is the accepted scientific name. Consequently, H. vulgatum is now classified as a synonym—a different name used to describe the same taxon.
Physical Description
Common Hawkweed is a versatile plant with several distinguishing morphological features:
Stem and Foliage
The plant typically grows between 4 inches (10 cm) and 36 inches (91 cm) in height. It features a short, stout rhizome (an underground plant stem that sends out roots and shoots). The leaves are broadly elliptic, reaching up to 5 inches (13 cm) in length, and they taper toward the base with characteristic teeth. The stalks below the flower heads are notable for being covered in scattered, simple, and gland-tipped black hairs, and they contain a milky substance.
Flowers and Fruit
During the summer months, the plant produces pale yellow flower heads. Each head consists of 40 to 80 ray florets (the petal-like structures), but notably lacks disc florets (the central florets found in many other Asteraceae). The receptacle—the basal part of the flower where florets are attached—is flat and naked. While the flower heads often begin in clusters, they tend to become solitary on long, leafless stems. The plant's fruit consists of dark brown achenes (small, dry, one-seeded fruits).
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Global Distribution and Habitat
Hieracium lachenalii is highly adaptable and is frequently found in disturbed soils, where competition from other vegetation may be lower.
Europe
As a native species, it is widely distributed across the European continent, including countries such as Austria, France, Germany, Italy, Norway, Poland, Spain, Sweden, the United Kingdom, and Russia, among many others.
North America and Australia
The species has been introduced to temperate regions of North America and Australia. In North America, its presence spans from Greenland and Canada (including British Columbia, Ontario, and Quebec) to various United States states such as Maine, Michigan, New York, Oregon, and Washington.
Summary of Botanical Classification
| Rank | Classification |
|---|---|
| Kingdom | Plantae |
| Clade | Embryophytes, Tracheophytes, Angiosperms, Eudicots, Asterids |
| Order | Asterales |
| Family | Asteraceae |
| Genus | Hieracium |
| Species | H. lachenalii |
Frequently Asked Questions
What is the difference between ray florets and disc florets?
In the Asteraceae family, ray florets are the outer, petal-like flowers of a composite head, while disc florets are the small, tube-shaped flowers located in the center. Hieracium lachenalii possesses ray florets but lacks disc florets.
Is Common Hawkweed considered an invasive species?
While native to Europe, it has become established as a weed in Australia and parts of North America, where it can thrive in disturbed environments.
Why was the name H. vulgatum changed?
Under taxonomic regulations, the oldest validly published name takes precedence. Since H. lachenalii was named in 1802 and H. vulgatum in 1819, the former is the correct scientific name.
When does Common Hawkweed bloom?
The pale yellow flowers of Hieracium lachenalii are produced throughout all the summer months.
What does a rhizome do for this plant?
A rhizome is a short, stout underground stem that allows the plant to store nutrients and spread by producing new shoots and roots.