Hayfield Tarweed

Woodrush Tarweed
Hemizonia congesta ssp. luzulifolia
NATIVE/ENDEMIC

Description (Jepson, PlantID.net)

• Eudicotyledon
  • Eudicots are a major lineage of flowering plants; see family for general characteristics
• Sunflower Family (Asteraceae)
• Annual herb
  • Whole plant with gland-tipped (sticky) hairs
  • Strongly aromatic
• Leaves
  • Linear, with gland-tipped (sticky) hairs
  • Lower leaves form a basal rosette
  • Upper leaves alternate (1 leaf at each junction with stem)
• Flowers
  • Inflorescence (flower arrangement) in open clusters of radiate heads (see Sunflower family), each head with 2 kinds of flowers
    • Ray flowers (5-11) are white and female (pistillate), with pink stripes on underside
    • Disk flowers (5-60) are white and male (staminate), with black-purple anthers (pollen-producing parts)
  • Phyllaries (vase-like floral bracts, collectively called the involucre) are hairy and glandular (sticky)
    • In a single series (row), one for each ray flower
  • Ovary inferior (below the attachment of other flower parts)
    • Each ovary is half enfolded, pocket-like, by a phyllary
• Fruit is an achene (a single-seeded, dry fruit that does not split open), more specifically called a cypsela because of the inferior position of the ovary 
  • Only ray flowers produce fruits
• Height to 31 in.

Distribution

• Native and endemic (limited) to California
  • Grows in grasslands, often in clay and serpentine soils
  • See Calflora for statewide observations of this plant
• Grows at elevations to 3,280 ft.

Uses (San Mateo County Parks prohibits removal of any natural material)

• Wildlife
  • Frequented by insects for pollen and nectar, e.g. hover flies (Syrphidae sp.), sweat bees (Halictidae sp.), small heliothodes moth (Heliothoides diminutiva), and the geometrid moth Cyclophora dataria
  • Seeds provide food for small mammals, e.g. mice, and numerous birds, e.g. mourning dove (Zenaida macroura), California quail (Callipepla californica), California towhee (Melozone crissalis), and dark-eyed junco (Junco hyemalis)
• Native people
  • Seeds of tarweeds (Hemizonia and Madia species), which are abundant, aromatic, and rich in oil, were a prized component of pinole for many California native peoples (Lowry 2009)
    • Pinole is a general term for various flours made from the ground, toasted seeds of wildflowers and grasses, eaten dry or moistened and shaped into balls or cakes (Anderson 2005)
    • “Pinole” is a Hispanic version of an Aztec word
  • Harvesting, done by women moving across fields and beating seeds into baskets, could occur before or after fields were burned to stimulate regrowth (Anderson 2005; Williams 2003)
    • If fields were burned before harvesting, the seeds were already roasted when beaten from the scorched, still-standing, but no longer sticky plants (Williams 2000)

Name Derivation

• Hemizonia (hem-i-ZONE-ee-a) – from the Greek hēmi, “half,” and zóni, “belt or girdle,” referring to the fruit that is half enclosed by the phyllaries
• congesta (kon-JES-ta) – from the Latin for “arranged closely together”
• luzulifolia (LUZ-yoo-lee-FO-lee-a) – from the genus Luzula, hairy wood rush, and folium, “leaf,” meaning “with leaves like those in the genus Luzula, ”possibly referring to the shiny appearance of the glandular hairs
  • The name of the wood rush genus Luzula may be derived from the Latin luzulae, a diminutive of lux, “light,” as the hairs of several species have a shiny appearance when covered with dew
• Tarweed – from the sticky nature of the tar-like oils of mature plants

Adaptations

• Well-adapted, like most tarweeds, to flower and fruit during our Mediterranean climate’s long dry summers and autumns (Lowry 2009)
  • Develops deeper roots than most annuals to capture ground water before bolting 
  • Resinous glands on the tips of trichomes (plant hairs) increase humidity
  • Mucilage (a thick, gluey substance) in stems and leaves retains moisture
  • Late-summer blooming ensures few competitors for pollinators
• Fruits, produced only by the ray flowers, are each cupped by a glandular (sticky) phyllary, aiding in the seed’s dispersal by catching onto passing animals
• Terpenes, a group of chemical compounds exuded from glands, deter herbivory (Grenada 2017)
  • Cattle enjoy young plants, but eschew mature, highly glandular plants, causing some ranchers to kill tarweeds (Lowry 2009)
• Terpene-exuding glands also provide an indirect defense against herbivory
  • Glandular plants are visited by various large and small herbivorous insects
  • Smaller insects, e.g., aphids and small flies, are trapped by the sticky glands and attract predatory insects, e.g., the spine-collared assassin bug (Pselliopus spinicollis)
  • Predatory insects also eat larger visiting insects, e.g., some weevils and mealybugs, and the small heliothodes moth caterpillar (Heliothodes diminutiva), that would otherwise eat the tarweed
  • In a controlled study, UC researchers found that hayfield tarweed and common madia plants with trapped insects produced more flowers and seeds (LoPresti 2017)
  • Watch this short video showing the assassin bug in action (KQED 2021)
• The pattern of purple-red striping on the backside of the ray flowers corresponds, like unfolded origami, to the lobes exposed to the sun on the closed bud
  • The color may be generated by anthocyanins, used by many plant species to protect tissues from excessive solar radiation

Notes

• The Tarweed-Silversword subtribe (Madiinae) includes some 127 species, principally in California, where it likely originated, and Hawaii (Flora; Baldwin 2000)
  • California’s tarweeds are traditionally called “true tarweeds”
    • Most species are summer-flowering annuals in summer-drought habitats
    • Leaves and phyllaries are usually hairy and glandular
    • Most species have radiate heads of yellow or white flowers
    • Each phyllary cups or encloses a single ray flower
    • Anthers are usually dark
    • Chaffy bracts usually create a ring between the ray and disk flowers
  • Edgewood has 10 tarweeds in 5 genera
    • Achyrachaena species: blow-wives (A. mollis)
    • Hemizonia species: hayfield tarweed (H. congesta ssp. luzulifolia)
    • Lagophylla species: common hareleaf (L. ramosissima)
    • Layia species: tidy-tips (L. platyglossa), tall layia (L. hieracioides), and woodland tidy-tips (L. gaillardioides)
    • Madia species: common madia (M. elegans), threadstem tarweed (M. exigua), slender tarweed (M. gracilis), and coast tarweed (M. sativa)
• Many Californians consider the smell of hayfield tarweed–love it or hate it–“the smell of summer”
• Edgewood’s hayfield tarweed is classified as a subspecies
  • Subspecies indicates a geographically-separated population with distinct morphological characteristics; when not isolated, interbreeding is possible
  • Variety indicates a population with small morphological variations, e.g. color, seen throughout the geographic range of the species; interbreeding is possible
  • In practice, botanists have not consistently applied these ranks

ID Tips

• Hayfield tarweed is white rather than yellow, as are most tarweeds, and is the dominant flower in Edgewood’s grasslands from late summer through fall

At Edgewood

• Found in non-serpentine and serpentine grasslands
  • See iNaturalist for observations of this plant
• Flowers May – December

Specific References

Anderson, M. K. 2005. Tending the Wild. University of California, Berkeley.

Baldwin, B.G., and B.L.Wessa. 2000, Dec.1. Origin and relationships of the tarweed-silversword lineage (Compositae-Madiinea). American Journal of Botany.

California Native Plant Society Yerba Buena Chapter. The tarweeds.

Granada Native Garden Newsletter. 2017, Oct. 15. Tarweeds — and their evil cousin!

KQED San Francisco. 2021, Sept. 8. You can’t unsee the assassin bug’s dirty work [Video]. Deep Look. YouTube.

LoPresti, E., B. Krimmel, and I. Pearse. 2017, Dec. 20. Entrapped carrion increases indirect plant resistance and intra-guild predation on a sticky tarweed. Abstract. OIKOS.

Lowry, J.L. 2009, July 1. The scent of summer. Bay Nature.

Prigge, B.A., and A.C. Gibson. 2013. Hemizonia congesta ssp. luzulifolia. A Naturalist’s Flora of the Santa Monica Mountains and Simi Hills, California. Web version, hosted at Wildflowers of the Santa Monica Mountains National Recreation Area. United States Department of Interior, National Park Service.

Williams, G. W. 2000. Early fire use in Oregon. Fire Management Today 60(3): 13-20.

Williams, G. W. 2003. References on the American Indian use of fire in ecosytems. Intertribal Timber Council.

General References

Calflora Database. 2014. Berkeley, California.

Calscape. 2018. California Native Plant Society.

Charters, M.L. 2015. California Plant Names: Latin and Greek Meaning and Derivations.

Charters, M.L. 2017. Southern California Wildflowers: Guide to the Pronunciation of Specific, Generic and Family Names.

Corelli, T. 2004. Flowering Plants of Edgewood Natural Preserve (2nd. ed.). Monocot Press, Half Moon Bay, California.

Elpel, T.J. 2013. Botany in a Day: The Patterns Method of Plant Identification. HOPS Press, Pony, Montana.

Flora of North America. efloras.org.

Harris, J.G., and M.W. Harris. 2013. Plant Identification Terminology: An Illustrated Glossary. Spring Lake Publishing, Spring Lake, Utah.

Keator, G. 2009. California Plant Families. University of California Press, Berkeley and Los Angeles, California.

Native American Ethnobotany DB.

Regents of the University of California. Jepson eFlora. Jepson Herbarium. University of California, Berkeley.