Achillea
millefolium L.
Standardized Common
Name: Yarrow
Other Common Names: Milfoil, Soldiers’
Woundwort, Thousandleaf
Family: Asteraceae
(Compositae)
Taxonomy: Achillea
includes something over 100 species of herbs, many of which are cultivated or
used medicinally. The genus is native to Eurasia, with a few species spreading
to northern Africa and North America. Its taxonomy is difficult, as species are
variable and often hybridize. The Achillea
millefolium species complex includes eight European species, microspecies
or subspecies, whose boundaries and status are unclear. Of those, A. collina J. Becker ex Reichenb. and A. pannonica Scheele are most frequently
treated as subspecies of A. millefolium,
but some might prefer to treat the whole group as one species. The European A. millefolium as most narrowly defined,
which is still quite variable, includes three subspecies, of which two are
widely distributed. Hybridization among forms and variation in ploidy level are
common.
The
native North American yarrow is also usually placed within A. millefolium as subsp. lanulosa
(Nutt.) Piper. It too was formerly divided into multiple species, including A.
lanulosa Nutt., A. nigrescens (E. Mey.) Rydb., and A. borealis
Bong., based on variations in ploidy and morphological features, but these
divisions are not well supported. Hybridization and morphological overlap among
the native and introduced European forms often obscure the origin of any
particular population. Chemical variation exists both among and within species
and subspecies. The European subsp. alpestris (Wimm. & Grab.) Gremli
is chemically distinctive, with leaf flavonoid content high in rutin. This and
subsp. lanulosa are said to be the only representatives of A.
millefolium (in the narrow sense) to contain azulenes, but variation within
subsp. millefolium is inadequately understood.
Description: Perennial herb.
Stems erect, clustered, 8–60( –90) cm high, occasionally branched near apex,
pubescent with long soft hairs. Leaves basal and alternate; basal leaves
petiolate, 10–25( –40) cm long; stem leaves subsessile to clasping, to 8 cm
long, usually >2 cm wide. Leaves lanceolate to oblong, deeply and finely
2–3-pinnatisect or pinnatifid, usually pubescent at least beneath; stem leaves
mostly with >15 pairs of primary segments; terminal lobes linear, crowded,
usually extending above and below plane of leaf and overlapping. Inflorescence
a terminal corymb, 2–30 cm broad, flat-topped to convex, dense, containing numerous
heads, sometimes subtended by few linear bracts. Heads with 4–6 ray florets,
about (3–)8–12(–20) disk florets. Involucre ovoid to cylindric, 3–4.5(–6) mm
long; receptacular bracts (phyllaries) in 2–3 whorls, oblong, obtuse, keeled,
sparsely pubescent, dull pale green with scarious margins. Receptacle flat to
slightly convex, elongating after flowering, bearing bracts (paleae); paleae
oblong, almost as long as disk florets, transparent. Ray florets female;
corollas usually white, to pink or purple; ligules 1–2 mm long, broadly
elliptical to almost circular, reflexed, 3-toothed. Disk florets perfect, ca. 4
mm long; corollas yellow or rarely white, tubular to narrowly campanulate
above, 5-toothed; pappus absent. Achenes oblong, flattened, shiny, at maturity
dark brown with narrow white wing around margin.
Parts in Commerce: Leaves and flowers
Identification:
Leaves
- Leaves
2–3-pinnately lobed or divided
- Largest leaves
petiolate, from the basal rosette; stem leaves sessile or with very short
petioles
- Leaves
lanceolate, not ovate or elliptical; stem leaves <8 cm long,
<2(–2.7) cm broad
- Primary lobes
divided more than halfway to midrib of leaf, but not divided entirely to
midrib in A. millefolium sensu stricto
- Most leaves with
at least 15 pairs of primary lobes
- Ultimate lobes
of leaves numerous, ovate to lanceolate or nearly linear, with
minute-pointed apices
- Lobes usually
extending above or below plane of leaf and curling when dried, giving a
characteristic three-dimensional appearance
- Midrib of leaf
in A. millefolium sensu stricto not over 1 mm broad, rarely toothed
- Leaves pale
grayish green; usually bearing long soft white hairs on both surfaces and
tiny round glands that may be visible especially on underside in less
hairy material
- Odor aromatic, characteristic
- Taste bitter
Inflorescences
- Corymb of heads
(capitula), variable in size
- Each head has
involucre of 2–3 whorls of phyllaries; 4–6 ray florets; several disk
florets
- Involucre
ovoid-cylindrical, 3–4.5(–6) mm high; phyllaries in 2–3 whorls, keeled,
with scarious margins, usually bearing some long soft hairs
- Receptacle of
head bearing chaffy bracts (paleae)
- Ray florets with
narrow tube and broad ligule; ligule reflexed, rounded, 1–2(–2.5) mm long
(rarely to 4 mm in some North American material), the apex with 3 small
rounded teeth
- Ligules usually
white, rarely pink; usually pink to rose or purple in A. millefolium
subsp. alpestris (likewise in four of the related European
microspecies)
- Disk florets
yellow or rarely white, perfect, ca. 4 mm long; corolla tubular, slightly
widened above, usually slightly flattened and with a basal swelling;
corolla teeth 5, acute
- Florets lack a
pappus
Subspecies of A.
millefolium: It may be desirable to distinguish among the three
widely distributed subspecies of A. millefolium sensu stricto (although
there remains considerable morphological as well as chemical variation within
subspecies). The following characters are often, though not always, reliable:
|
subsp. millefolium
|
subsp. alpestris
|
subsp. lanulosa
|
Geographic origin
|
Europe, naturalized in North America
|
Europe, possibly dispersed to North America
|
North America
|
Inflorescence
|
Corymb flat-topped to somewhat rounded
|
Corymb flat-topped to somewhat rounded
|
Top of corymb conspicuously rounded
|
Ligule color
|
White; rarely pink, especially in cultivation
|
Pink
|
Usually white
|
Margin of involucral bracts
|
Pale to medium brown
|
Dark brown to black
|
Usually pale, but sometimes dark brown in northern
hexaploid material
|
Pubescence of vegetative parts (hairs always long,
soft, white)
|
Hairy to nearly glabrous
|
Hairy to nearly glabrous
|
Very hairy
|
References:
Bugge G. Untersuchungen der Sippen des Achillea-millefolium-Komplexes
auf Azulengehalt und Ploidiegrad. Angew Bot. 1991;65:331–339.
Ehrendorfer F. New chromosome numbers and remarks on
the Achillea millefolium polyploid complex in North America. Österr
Bot Z. 1973;122:133–143.
Fernald ML. Gray’s Manual of Botany, 8th ed. New York: American Book
Company; 1950:1514–1515.
Gervais C. Cytological investigation of the Achillea
millefolium complex (Compositae) in Quebec. Canad J Bot.
1977;55:796–808.
Guédon D, Abbe P, Lamaison JL. Leaf and flower head
flavonoids of Achillea millefolium L. subspecies. Biochem Syst Ecol.
1993;21:607–611.
Kokkalou E, Kokkini S, Hanlidou E. Volatile
constituents of Achillea millefolium in relation to their infraspecific
variation. Biochem Syst Ecol. 1992;20:665–670.
Richardson IBK. Achillea.
In: Tutin TG, Heywood VH, Burges NA,
et al., eds. Flora Europaea. Vol. 4. Cambridge:
Cambridge University Press; 1976:159–165.