1. Dipsacus L. (teasel)
Plants biennial.
Stems erect, several-angled or ridged, prickly, often somewhat shiny. Leaves
basal and opposite, those of the basal rosette sessile to short-petiolate,
those of the stem sessile, those of a pair sometimes fused at the base.
Stipules absent. Leaf blades simple, entire to bluntly toothed or irregularly
pinnately lobed along the margins, sometimes also prickly, the undersurface
prickly along the midvein, those of the basal leaves to 50 cm or more long,
often withered or absent by flowering time, those of the stem leaves
progressively reduced toward the stem tip. Inflorescences ovoid to cylindrical
heads of numerous dense flowers, subtended by 1 or 2 whorls of involucral
bracts of unequal lengths, these curved upward, prickly along the midrib and
margins, and tapered to a spinelike tip. Flowers perfect, epigynous, somewhat
zygomorphic, each subtended by 1 receptacular bract (this with the body
lanceolate to oblong-ovate, tapered abruptly at the tip to a long [to 25 mm],
slender, loosely ascending, spinelike awn, persistent after the fruits have
been shed) and enclosed in a 4-ribbed involucel of fused bractlets (this about
as long as the ovary, truncate or obscurely 4-toothed at the tip, shed with the
fruit). Calyces cup-shaped, sometimes somewhat 4-lobed, somewhat 4-angled,
densely silky-hairy, persistent at fruiting. Corollas 4-lobed, densely minutely
hairy on the outer surface, with a long, slender tube, the lobes relatively
short, oblong, rounded at the tip. Stamens 4, alternating with the corolla
lobes, exserted, the filaments slender, attached at the corolla base, the
anthers attached toward their midpoints. Staminodes absent. Pistil 1 per
flower, of apparently 1 carpel (a second carpel aborting early in development).
Ovary inferior, with 1 locule, the placentation terminal. Style 1 per flower,
the stigma 1, positioned laterally at the style tip. Ovule 1. Fruits achenes,
somewhat flattened, mostly hidden by the persistent involucel. Ten to 12
species, Europe, Asia, Africa, introduced in North America.
In Europe, the
dried heads of fuller’s teasel, D. sativus (L.) Honck., formerly were
used (after the fruits had been shed) to raise the nap in fulling cloth and
were cultivated on a limited basis. However, plastic substitutes now are
generally used for this purpose. This species, which escapes only rarely in the
northeastern United States, differs from D. fullonum in its receptacular
bracts with strongly recurved awns. Both of the Dipsacus species
naturalized in the state were officially designated as noxious weeds by the
Missouri state legislature in 2000. Although these plants are occasionally
cultivated in gardens, this practice is considered illegal and is to be
discouraged. Similarly, the use of the fruiting heads in dried flower
arrangements should be discontinued.