The qimmos and its closely related word qimmashon have been translated as ‘brier’, ‘nettle’ and ‘thorn’. What is clear is that it was some type of stinging plant.
This could be a member of the Urtica species, possibly the membranous nettle Urtica membranacea which is often found among ruins, this fits the image from Isaiah and Hosea.

Ammi visnaga

The flower of the 'Ammi visnaga'. PICTURE: Dwight Sipler (licensed under CC BY 2.0)

Ephraim Hareuveni thought it was a member of the Umbelliferae family, the Ammi visnaga because "this plant quickly spreads over abandoned wheat fields" as per Proverbs 24:30-31. 

The Ammi visnaga is an annual (or sometimes biennial) plant growing from a taproot to about 80 centimetres in height. The leaves grow up to 20 centimetres long and are generally triangular or oval in shape. 

There is another possibility: that the qimmos/qimmashon could belong to the Xanthium genus. Two species of plants from this genus that are found in Israel are Xanthium strumarium (the cocklebur) and Xanthium italicum

There are two references to qimmos and one to qimmashon in the Old Testament. The NIV translates qimmos as as ‘nettles’ and ‘briers’ and qimmashon as ‘weeds’. 

The references include:

"Thorns will overrun her citadels, qimmos [nettles] and brambles [choach] her strongholds. She will become a haunt for jackals, a home for owls." - Isaiah 34:13.

"Even if they escape from destruction, Egypt will gather them, and Memphis will bury them. Their treasures of silver will be taken over by qimmos [briers], and thorns [choach] will overrun their tents." - Hosea 9:6

The field of a lazy man will be overcome by qimmashon.​
I went past the field of a sluggard,
past the vineyard of someone who has no sense;
qimmashon [thorns] had come up everywhere,
the ground was covered with weeds [charul],
and the stone wall was in ruins. - Proverbs 24:30-31

This is an edited excerpt from Alvin Johnson's iBook 'Biblical Flora', 2017. The book is available for free download on iTunes. A teacher's edition is also available for purchase.