The genus Bidens Linnaeus
The words or terms in red
(actually dark orange) in the text are defined in a
Bidens is a genus of weedy herbs
with over 200 species.
The genus belongs to the Heliantheae
tribe of the
It was described by Linnaeus (1701-1778) in his Species Plantarum, 1753.
The genus is distributed throughout the world.
About 50 species, including introduced ones can be found in the USA.
A dozen of species, flowering at the end of summer and in the fall
can be found in Québec, some quite common.
The species of Bidens that is best known to
botanists, horticulturists and
herbalists is Bidens pilosa.
It is used as an herbal medicine in many parts of the world.
It is commonly found growing along roadsides, railroad
tracks, vacant lots, and other places where the ground has been disturbed,
including the shores of rivers of ponds.
In Latin, bis means twice and dens means tooth so
that bidens means two-toothed; hence the genus name refers to the
bristles of the
achenes of the plants,
even if these seeds have, at times, three or four bristles.
Many species found in North America have the common names
Bur-marigold, Sticktights, Beggar-ticks, Beggartick, Railway Beggar's Tick,
Devil's Sticktight, Spanish Needles, Tickseed-sunflowers,
the first vernacular name
referring to the color of the flowers,
the other ones referring to the achenes commonly functioning as
stick-tights in animal fur and clothing, in feathers, by means of their
barbs. This distinctive dispersal
adaptation explains the widespread, distribution and colonization of the genus.
Some Bidens species have also been known with an other genus name:
- Campylotheca Cass.
- Coreopsis L.
- Microlecane Sch. Bip. ex Benth. & Hook. f.
- Oparanthus Sherff
- Petrobium R. Br.
The Bidens genus is distinguished by the combination of:
Some species have divided leaves with toothed segments and long
ray flowers; others have undivided,
lance-shaped leaves and short ray flowers or none at all.
- awned seeds,
- opposite leaves
(but for the uppermost),
- dimorphic involucral bracts,
with an outer set of longer, herbaceous bracts and an inner set of
Bidens species comprise annual and
perennial herbs and
vary greatly in size and degree of branching.
Leaves may be
they are opposite
(or alternate for the uppermost),
obscurely to coarsely serrate,
The flower heads are
The ray florets, when present,
are rather few, sterile or rarely
pistillate and have
The involucral bracts are biseriate
and dimorphic, the outer row being usually foliaceous and spreading, while the
inner is row short,
The disk florets are
perfect, usually numerous and with a usually
yellow corolla but for some species
a white corolla.
The fruits are flattened achenes, narrowed at the base and widening upward,
with 2 to 4 retrorsely barbed awns
which persist atop the achene, the fruits functioning as stick-tights in animal
fur and clothing by means of the barbs.
Several species of Bidens were used as sources of the traditional Chinese
medicinal herb; they were known as guizhencao, where gui means
demon or ghost, zhen means spike, needle and
cao means weed, plant, the name making reference to the
characteristic barbs on the fruits. The barbed fruits of these herbs are used as
medicine and must be handled carefully or they can cause injury. Descriptions of
injuries from Bidens spikes (mainly infection from cuts received) have
appeared in the medical literature.
In Europe some Bidens species were used in the 16th and 17th century
for their astringent,
Bidens frondosa and Bidens bipinnata were prescribed in the U.S.
as emmenagogue and in the treatment of
laryngeal and chest complaints.
Some Bidens species are used as food plants by the larvae of some
Bidens pilosa, an annual native
to tropical America, is one of the world's worst weeds.
The Bidens of Québec
In Québec one should find the following species:
Quite often, it is difficult to identify with certainty each species,
and one must be very careful before attributing a name to a given specimen;
Bidens are well known for
the species having plastic phenotypes.
- Bidens beckii
Bidens cernua (picture above)
- Bidens connata
- Bidens discoidea
- Bidens eatonii
- Bidens heterodoxa
- Bidens hyperborea
- Bidens pilosa
- Bidens trichosperma
- Bidens tripartita
- Bidens vulgata