Tarweed

Tarweed (or fascicled tarweed or slender tarweed; Deinandra fasciculata) is a California native growing from central California to lower Baja California. Tarweed is one of the yellow fellows of summer, slipping into the trailside parade just after yellow pincushion and before goldenbush. In open areas it produces fields of bright yellow flowers that last well into the dry season.

Tarweed exudes resin, thereby giving tarweed its common name. The resin is thought to reduce water loss from plant tissue during the long dry summer. A cut tarweeed flowering stem will remain fresh without water for two to three days

Description ^2,4,43,59

Tarweed is an upright, branching annual plant, usually less than 3 ft (1 m) in height. In early spring, a basal rosette of leaves develops from a taproot; basal leaves may be up to 6 inches (15 cm) long.  Later, upright reddish stems arise, branching mostly above the midpoint. Basal leaves generally wither before flowering begins, and the cauline leaves drop soon after. The small narrow cauline leaves are irregularly and coarsely toothed with the margins rolled under. Stems and leaves are more or less covered with white hairs. Plant are glandular, producing a sticky resin with an aroma that varies from unpleasantly pungent to pleasantly sweet seemingly dependent on the age of the plant and strength of its odor.

Flower heads are composite, like a daisy, with two types of florets clustered together on a common base. The five peripheral ray florets each have one, broad, three-lobed petal flaring outward. Several (usually six) symmetrical, urn-shaped disk florets form the “eye” of the flower head. Ray florets are female with single pistles which have two-branched styles. Disk florets are bisexual, often with dysfunctional pistils. Five dark anthers are united into a column around the style; when mature, these form five distinctive dots in the eye of the flower head. Small clusters of yellow flower heads are born at the ends of branches. Together with the long stems and sparse foliage, the small terminal clusters of blooms give the plant an open, airy look. The major bloom time is April – September.¹

After fertilization, petals wither but remain attached. Seeds are tiny, lacking a developed pappus to parachute them through the air, away from the parent plants. They are presumably dependent on gravity or on birds and small animals for dispersion.

Classification  

Tarweed is a dicot angiosperm in the sunflower family, the Asteraceae.^2,11 This is the largest family of vascular plants in the Northern Hemisphere.¹⁴³ “Flowers” of Asteraceae are made up of one or both of two types of flowers (florets): symmetrical disk florets and strapped-shaped ray florets. These are crowded onto a common base (receptacle), and together they are often assumed to be a single flower, which we call a flower head.^11,44,49,143

Other familiar Asteraceae that occur in the Reserve include bush sunflower (Encelia californica), goldenbush (Isocoma menziesii) and California sagebrush (Artemisia californica).⁴⁸

Originally classified in the genus Hemizonia, tarweed and closely related species were moved into a new genus Deinandra.⁴³ They are distinguished from many other Asteraceae by having both ray and disk florets and by details of the structure of the floret.

Ecology ^43,175

Many plants in the Reserve, especially plants like tarweed that bloom during the summer and fall, exude strong-smelling resins.  Resins are complex mixtures of organic molecules and are presumed to give the plant a survival advantage in seasonally dry environments. The resin of relatives of our tarweed (also call tarweeds; Holocarpha spp.) contains compounds that slow water loss across cell membranes, thus retarding water loss from plants during long dry summers. Tarweed resins also have compounds that can be toxic, deterring grazers, especially important during the late summer when many plants have done dormant. Resins have other compounds that absorb ultraviolet radiation and may provide protection from sun damage.

Human Uses  

The Chumash, near Santa Barbara and the Channel Islands, gathered and dried the tiny black seeds and winnowed away the chaff. They then pounded the seeds with a little water and formed a ball which they usually ate raw.¹⁵ Seeds were also used in Pinole, a flour-like substance that was used dry or in gruel.^15,67 In case of hunger, many Indians boiled the entire plant down to a thick, tarry mass that was eaten.¹⁷⁵

The local Kumeyaay used tarweed to cure headaches, boiling the plant in water and inhaling the steam, either in a sweathouse or the modern way – under a towel over a pan.^16,67 The Chumash tied several slender tarweed plants into a bundle two to three feet long for a broom.¹⁵

Interesting Facts  

Tarweed is a very common common-name. Many tarweeds (and tarplants), including ours, belong to a group of related genera in the sunflower family.⁵⁹ Most of these plants get their name from the copious resins they produce, which are said to stain clothes.²³  (Note from EV: In fact the stain is yellow-green – not what I expect from tar.)

It may be the resins that prevent the plants from losing their petals after fertilization. Prigge and Gibson⁴ write “Slender tarweed seems able to resist drying and blooms when growing in dry soil, and a severed shoot will continue to flower for days, even if not kept in water…” The middle photo below shows a small branch of tarweed about one hour after collection. It is in a glass without water. The dry plant continued to look fresh for three days, even producing a new flower (right photo). By the fourth day, all the blossoms looked wilted but were still flexible and no petals had been lost. On the fifth day, the cleaning lady threw out the experiment.