Some of the UK’s rarest plants are at risk of extinction unless action is taken to look after the road verges that have become their final refuge, a charity has warned.

Species such as fen ragwort and wood calamint are now only found on road verges, with fen ragwort hanging on in just one native spot near a burger van on the A142 in Cambridgeshire, conservation charity Plantlife said.

Other plants such as sulphur clover, crested cow-wheat and wood bitter-vetch have lost much of their habitats in meadows, pastures or woodlands and are now most frequently found on the side of roads.

In total, Britain’s verges are home to more than 700 species of wild plants, with 12% threatened with extinction or heading in that direction, Plantlife said.

Wood calamint is one of the species found only on road verges. Photograph: M Cotterill/IWNHAS/Plantlife/PA

Some verges are effectively fragments of wildflower-rich ancient hay meadows and grasslands, most of which have been lost through the countryside since the 1930s, while coastal plants have exploited motorways and A-roads that are salted in winter.

The wildflowers provide nectar and pollen, and are a refuge for many declining bee, butterfly, bird, bat and bug species, with plants such as bird’s-foot trefoil – a food source for 160 species of insect – found on many verges.

Plantlife has revealed the top 10 threatened species growing on Britain’s road verges, as it calls for better road verge management to help protect wild flowers and plants. The list includes among others the species tower mustard, velvet lady’s-mantle, yarrow broomrape and Welsh groundsel.

The charity also said road verges were an important connection to nature for people, with their flowers from bluebells to knapweed providing colour and a sense of the seasons through the year.

Trevor Dines, Plantlife’s botanical specialist, said: “For too long road verges have been thought of as dull, inconsequential places that flash by in the wing mirror.

“But these findings underline just how fundamental verges are to the health of wildflowers and the wildlife they support.

“Sadly, road verges have been woefully disregarded for decades and are increasingly poorly managed for nature.”

He said some very rare plants were “hanging on” thanks to the existence of some well-managed verges.

Intensive agriculture has meant sulphur clover is more easily found next to roads instead of grassy pastures. Photograph: Andrew Gagg/Plantlife/PA

“But we must not get complacent – only genuine management for nature will safeguard these and other plants from extinction.”

He added that the plight of the critically endangered fen ragwort was “particularly striking”.

“Only one native site remains but, unlike lady’s-slipper orchid which also grows in a single native site and receives round-the-clock protection when in flower, this poor plant flounders in an unprepossessing roadside drainage ditch beside the A142 near Ely, Cambridgeshire, where it is at risk from discarded debris.”

He warned many councils were mowing road verges earlier in the year, which only gives early flowers a chance to set seed before they are mown, and later plants struggle to survive under the cuttings left behind. Simple changes to management such as mowing later can have a major difference.

Almost 20,000 people have signed Plantlife’s petition calling for council management to better benefit wild flowers, the charity said.