Yarrow is a common plant around Nanaimo, you’ll see it growing along roads, in lawns and dry meadows around town. The leaves are distinctive, feathery and silvery. The species name ‘mille’ ‘folium’ means ‘thousand’ ‘leaves’, and refers to the many tiny and finely divided leaflets per leaf.
Yarrow is found in most places in the Northern Hemisphere and it’s used as a medicinal plant wherever it is found. Crush a leaf, or rub a stem, and notice the aromatic smell. Steeping a bit of a leaf in hot water can soothe a sore throat. Yarrow, like many other aromatic plants, likely has antimicrobial properties, and even birds use it in their nest building (see e.g. https://www.nature.com/articles/news020715-14; http://w.evolutionhumaine.fr/pdf_articles/lafuma_2001_Behav_Processes.pdf)
Yarrow grows abundantly all over Nanaimo. You’ll often notice it along roadsides, as a weed in lawns, or in meadows. When not flowering, the plant can sometimes be mistaken for a fern. When casually observed, the basal leaves can resemble fern fronds. Photo credit: Lynda StevensThe leaf of yarrow is a distinctive character of the plant. The leaf is finely divided (‘pinnately dissected’) and arranged alternately along the stem. The leaf is smooth and silky to the touch. Photo credit: Lynda StevensYarrow flowers from late spring into late in the fall. If we’re careless, we might confuse yarrow with Queen Anne’s lace (Daucus carota), which also has white flower clusters, but a bit more careful inspection reveals many differences. Photo credit: Lynda StevensYarrow belongs to the family Asteraceae. The main distinguishing characteristic of this family is the flower structure. What appears like an individual white flower in the center of this photograph is really a ‘composite inflorescence’, a cluster of flowers packed tightly together. In that central “flower”, there are 4 ray flowers, each one carrying a single white petal, and 3 disc flowers in the center. See the diagram below for a better explanation of the architecture of a composite flower. Photo credit: Lynda StevensDiagram of the structure of composite flowers. There is a lot of specialized nomenclature associated with Asteraceae composite flowers. For our purposes, let’s focus on the existence of ray flowers (carrying petals and making the whole structure look showy and inviting to pollinating insects & people) and disc flowers that lack petals, but carry the male and female organs. (https://thenaturecollective.org/plant-guide/glossary/)A sunflower (Helianthus annuus) inflorescence is an example of a very large composite flower – this large yellow “flower” is analogous to one of the small white “flowers” of the yarrow. The yellow petals along the edge are associated with individual ray flowers, and the central disc consists of very many disc flowers. The disc flowers are in different stages of ‘anthesis’ (“flower-opening”). The disc flowers furthest from the center open first, and display their stamens, releasing their powdery yellow pollen. A while later, the female organ emerges from the center of each disc flower (difficult to see in this photo). Photo credit: David D Taylor
