Helminthotheca echioides, known as bristly (or prickly) oxtongue, is a sprawling annual or biennial herb native to Europe and North Africa. It was originally placed within the genus Picris but is often separated within the small genus Helminthotheca alongside a few other (mainly North African) plants which also have the distinctive outer row of bracts around the flowerheads. It is a ruderal plant, found on waste ground and agricultural soils around the world, and in some places it is considered a troublesome weed.
Description
Bristly oxtongue is an annual to biennial herb with an erect or sprawling habit that grows up to tall (often up to 150 cm in fertile soils and shady places), with a solid, furrowed stem and spreading branches. The basal rosette leaves are long, oblanceolate with a short petiole, whereas the cauline leaves are lanceolate and sessile with clasping, cordate bases. On the leaves and stem (especially on the basal leaves) there are distinctive sharp bristles, 2 mm long, with swollen whitish bases that resemble blisters. On other parts of the plant there is a scattering of smaller, anchor-shaped hairs with recurved double-pronged tips which make the plant feel sticky.
In northern Europe it flowers from May to October. The inflorescences arise on long stalks from the leaf axils in an irregular corymb. Each flowerhead is wide with numerous yellow ray flowers (the outer florets sometimes tinged red/brown). They are surrounded by three rows of involucral bracts: an inner ring which is narrow and blunt-tipped with a spiny awn that arises just below the tip; a middle ring of tiny bracts which are easily overlooked and sit at the base of the inner row (they are important in separating this from other species of Helminthotheca); and an outer ring which is made up of 3 to 5 large, ovate-cordate flaps that later surround the seed head. This outer ring of bracts are the defining feature of the genus Helminthotheca.
Helminthotheca echioides is said to be heterocarpic (i.e. it has fruits of two different shapes), however, not all authors report this. When it is so, the outer achenes (which are retained inside the closed-up seedhead after the central ones have dispersed) are slightly longer (7 mm) and curved, while the inner ones are only 5 mm long and straight. The normal achenes are yellow to orange or brown in colour and have transverse scaly ridges, and a narrowed tip (beak) about as long as the body, to which is affixed a pappus of two rows of white, feathery plumes which enable the seeds to be dispersed by the wind. Reproduction is believed to be apomictic, so the plants effectively clone themselves, but the flowers are also visited by bees.
Taxonomy
The genus Helminthotheca was originally described by the pre-Linnean author Sébastien Vaillant in 1754 but, because such names are ruled out by the Code of Nomenclature, the recognised author is Johann Gottfried Zinn, who listed it in his Description of the flora around Göttingen in 1757. However, Linnaeus had by this time already published a valid name for bristly oxtongue in Species Plantarum, so Linnaeus's name, Picris echioides, is the basionym and has precedence over the name Zinn used. Prickly oxtongue has therefore been assigned to two different genera from earliest days, but the combination of Zinn's Helminthotheca and Linnaeus's echioides was not formed until 1973, when the name was coined by the Czech botanist Josef Holub in a paper in the journal Folia Geobotanica & Phytotaxonomica. In the English-speaking world, endorsement for the new combination was given by Walter Lack in a paper in the journal Taxon in 1975.
Many other synonyms for Helminthotheca echioides have been coined over the years, which are listed in the International Cichorieae Network: Cichorieae Portal.
Modern molecular studies show that Picris and Helminthotheca are closely related. The studies are consistent with the current view that they be considered separate genera. Anatomically, they are separated mainly by the presence of an outer row of enlarged involucral bracts in Helminthotheca.
Its chromosome number is 2n = 10.
Helminthotheca echioides is not known to hybridise with any other species.
A number of infraspecific taxa have been described, varying in their leaf shape, although they are not widely accepted. Sell & Murrell list four varieties in Britain:
var. mollis (Duby) P.D. Sell, with large dentate but not incised leaves
var. pratensis (Chevall.) P.D. Sell, narrowly elliptical dentate leaves
var. echioides, with broadly elliptical leaves
var. incisa P.D. Sell, with large, deeply incised leaves.