SafePlants

Tarweed and Spikeweed: A Botanical Overview

This page explores various plants known as "tarweed" or "spikeweed," focusing on their taxonomy, distribution, and ecological roles. These names encompass several species within the Asteraceae (Sunflower) family, particularly those in the Madieae tribe.

Considerations for Pets

• Some tarweeds are described as "sticky" and "hairy" due to the presence of glandular trichomes.

Scientific Names and Common Names

• Several plants are referred to by the common name "tarweed" or "tarplant."
• Key species include:
  • Centromadia pungens: Commonly known as common spikeweed or common tarweed.
  • Madia elegans: Known as common madia, showy madia, or common tarweed.
  • Hemizonia fasciculata: Known as clustered tarweed.
  • Madia gracilis: Known as Common Tarweed or Grassy Tarweed.

Taxonomy and Nomenclature

• Family: Asteraceae (Sunflower family), also known as Compositae
• Tribe: Madieae (for some species)
• Synonyms/Alternative Names:
  • Hemizonia pungens (Hook. & Arn.) Torr. & A. Gray (synonym for Centromadia pungens)
  • Centromadia pungens subsp. pungens (Hook. & Arn.) Greene (subspecies of Centromadia pungens)
• Subspecies of Madia elegans:
  • M. e. densifolia - showy tarweed
  • M. e. elegans - common madia

Distribution and Habitat

• These plants are native to western North America, particularly California and the Klamath-Siskiyou bioregion.
• They are commonly found in grasslands, open areas, and seasonally flooded areas, such as those along the Cosumnes River.

Ecological Role

• Centromadia pungens ssp. pungens is listed in "Invasive Species Most Unwanted."
• Tarweeds have adaptations, such as an annual habit, that allow them to thrive in summer-dry environments.

Morphological Characteristics and Growth Habits

• Madia elegans is described as an erect annual with hairy, branching stems and narrow, linear to lance-shaped leaves. It has yellow, daisy-like flowers that open in summer and close by mid-morning.
• Madia gracilis has spicy foliage and small, yellow flowers.
• Some tarweeds have glandular trichomes, giving them a sticky or hairy texture.

Interactions with Other Organisms

• Despite having glandular trichomes, common tarweed (species not specified) is visited by several types of predatory arthropods.

Quirky Facts

• Tarweed exudes resin, which is believed to reduce water loss during the dry summer months. This resin is the origin of the name "tarweed."

Further Information

• Encyclopaedia Britannica: Offers updated online encyclopedia articles.
• Dave's Garden: A community website for sharing gardening tips and ideas.