Home   eXtreme botany   Can you tell your Dipsacus from your Helminthotheca?

Can you tell your Dipsacus from your Helminthotheca?

Dr M has been reminded in his recent field surveys of two similar (but different!) rosette plants of disturbed ground, both with rough, blistery-bristly leaves and often found growing together, but which can be confused by the beginning botanist – even though they are from rather different families. So how to tell them apart?

The first of these is Helminthotheca echioides – you may know this by the synonym Picris echiodes – and common name Bristly Oxtongue in the Asteraceae (Daisy Family).

Very obvious when in flower, this is one of those yellow Asteraceae with yellow, dandelion-like inflorescence, but this one with very bristly leaves (like Echium (Boraginaceae) hence the specific epithet “echioides” meaning: looks (and feels) a bit like an Echium!).

Without flowers it is still identifiable from vegetative characters. The leaves are alternate, in a rosette, with some hairs on white swollen, blister-like bases. The hairs are often forked, bifid and sometimes trifid, and minutely hooked so that the plant easily becomes attached to woolly clothing (try it! But best to try it on enemies rather than friends, its hellish to remove from woolly clothing!).

The close-up image shows these hooked and trifid hairs, and also the translucent secondary veins, all good characters for separating this bristly leafed plant from the next one…

Dipsacus fullonum (Common Teasel) in the Dipsacaceae (Teasel Family).

Again this plant is very obvious and unmistakable in flower, it’s a tall, spiny plant with the characteristic  teasel inflorescence (teasels so-called because of their use in the textile industry for raising the nap on fine fabrics such as velvet) in dense heads upon a common receptacle with a calyx-like whorl of bracts below each head. The teasel inflorescence is very much reminiscent of the capitulum of the Asteraceae, not surprising then that Dipsacaceae is right next to Asteraceae in the taxonomic hierarchy.

Without flowers we can still ID from vegetative characters. The leaves are opposite (a feature of the family Dipsacaceae, so pretty conclusively different from Helminthotheca (Asteraceae) already!).

Leaves also have a spiny midrib below (not shown here but check it out yourself), and swollen based, stiff hairs both sides. The robust swollen based hairs here make the leaf bristly and rather like Helminthotheca, but there is nothing like the forked and hooked hairs of that plant.

Again the close-up image shows these swollen based stiff hairs, good characters for separating Teasel from the superficially similar Bristly Ox-tongue.

Click the images once, then a second time to see these hairs in fascinating detail!

So, in summary:

Bristly Ox-tongue (Asteracae): Alternate leaves, swollen based hairs which are forked (bifid or trifid) and hooked.

Teasel (Dipsacaceae): opposite leaves, swollen based stiff hairs, neither forked nor hooked.

There’s lots more if you check out the Veg Key and the Book of Stace for floral characters, but that’s enough for now, hopefully no more confusion between these two plants with bristly leaves, superficially similar, but, with the gift of hindsight and a hand lens, very different blistery-bristlies indeed!

And finally: the two plants in flower emphasises the blistery-bristly similarity and the floral differences between the two plants and the Asteraceae and Dispacaceae families.

 

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