Golden Yarrow

Golden yarrow (Eriophyllum confertiflorum) is native to the coastal sage scrub and chaparral along the west coast of California and northern Baja California. It is a medium, rounded plant that blooms in late spring with clusters of bright yellow flowers

The blossom of golden yarrow is actually a flower within a flower within a flower. What first appears to be a single flower, on closer inspection is seen to consist of several small, daisy-like flowers in a compound flat topped cluster. In turn, each “daisy” consists of two types of flowers. The eye of the “daisy” is formed of tiny symmetrical flowers (disk florets); each “petal” around the edge is a single, asymmetrical flower (a ray floret).

Description ^{4,11,23,26,43,59}

Golden yarrow is a subshrub usually less than three feet (1 m) high. There is a short taproot, but most of the roots are shallow, within the upper 1.5 feet (40 cm). One to several branching, upright or widely spreading stems form loosely upright to mounding cushions. Stems are covered with white wooly hairs and are reported to be aromatic,⁴ but we have not noticed an aroma from our plants. Leaves are relatively small, less than two inches (5 cm) long, sessile and deeply pinnately lobed one or two times, with one to three pairs of primary lobes. Leaf margins are rolled under. Leaves are green above, with sparse hairs; leaves below are covered with long, white wooly hairs. Conspicuous axillary buds are swollen, with a white wooly covering.

Flower heads occur in terminal flat-topped or domed compound clusters. Several principal branches end in clusters of 20 or fewer golden flower heads. The involucre is urn-shaped, of one series of ovate or obovate, green phyllaries.  Flower heads are 1/4 to 1/2 inches (0.7-0.9 cm) across, with 4-6 ray florets and 10 or more disk florets. The pappus is greatly reduced. A bilateral ray floret consists of a short tube with one small but conspicuous rounded petal. A ray floret lacks stamens; the pistil has a small, one-chambered inferior ovary, with a single style that extends slightly beyond the tube and has two strongly recurved branches. The symmetrical disk floret is bisexual, with a pistil similar to that of the ray floret. The stamens are united by the bright yellow anthers into a tube around the style. The peak flower time is March-August.¹

Classification

Golden yarrow is a dicot angiosperm in the sunflower family, Asteraceae.² 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: symmetrical disk florets and strapped-shaped ray florets. These are crowded onto a common base (receptacle) and together are called a flower head.^44,49,143 A flower head is often mistaken for a single flower. Other familiar Asteraceae that occur in the Reserve include California sagebrush(Artemisia californica), bush sunflower (Encelia californica), and goldenbush (Isocoma menziesii).⁴⁸

Species in the genus Eriophyllum are characterized in part by the presence of both ray and disk florets, by a single series of overlapping phyllaries beneath each flower head, by flower heads in more or less flat-topped clusters, and by a pappus that is absent or is reduced to a crown of jagged scales.²

Golden yarrow is a variable species with two varieties in California, separated by the number of flower heads in a cluster. The variety in the Reserve is var. confertifolium.⁴⁸

In spite of the common name and flat-topped flower cluster, golden yarrow is not closely related to common yarrow (Achilleamillefolium). Both are in the sunflower family, but that is a large family variously subdivided into subfamilies and/or tribes.^11,41,143 The two yarrow species belong to different tribes.¹⁴³

Ecology

Many plants of the coastal sage scrub respond to fire, not by vegetative resprouting (like many chaparral species) but by means of enhanced seed germination.³⁴⁵ In a recently compiled list,²⁸¹ the Golden Yarrow was reported to be among the 123 “Species that are always present but are much more abundant after a fire”. Some percentage of the seeds produced by golden yarrow need some stimulus to germinate. Fire and its by-products may be the main stimulus or one of several. In the absence of fire, approximately 25% of the golden yarrow seeds will readily germinate the following year; the rest remain dormant.⁴³ Both charred wood and leachate from ash have shown to be effective in breaking that dormancy. Thus golden yarrow is more abundant in post-fire areas, slowly being overgrown as the areas recover. Such species often take refuge between fires in smaller openings, trail edges, and disturbances.

Many disparate flowers in the Reserve are more frequent after a fire, often because their germination is stimulated by some component of fire. A of the more familiar are wind poppy (Papaver heterophyllum), California poppy (Eschscholzia californica), rock rose (Crocanthemum scoparium), wild morning glory (Calystegia macrostegia), rattlesnake weed (Daucus pusillus),  yellow pincushion (Chaenactis gabriuscula) and sacapellote (Acourtia microcephala).

Human Uses

There are relatively few reports of usage by Native Americans. The Kumeyaay boiled the whole plant and used the water as a face wash to treat pimples.¹⁶ The Cahuilla, from the inland area of Southern California, ground the parched seeds into flour.²⁸²

Today, golden yarrow is often used in habitat restoration and erosion control.⁴³ It is recommended for native plant gardens, where it is an important nectar source for a variety of insects.^{24,43,168,290}

Interesting Facts ²¹

The scientific name of golden yarrow, Eriophyllum confertiflorum, provides more description than many scientific names.
Eryophyllum is derived from the Greek words “erion”, meaning wool, and “phyllon”, meaning leaf; together they describe the long wooly hairs that cover the stem and lower leaf surfaces. Confertiflorum comes from the Latin “confertus”, which means crowded and “flora”, meaning flowers which refer to the number of florets on a flower head, and/or the number of flower heads in a cluster.