Linaria, Chaenorhinum and Cymbalaria species - Toadflaxes
Linaria vulgaris - Common Toadflax
This has a soft, flexible stem and leaves which are slightly glaucous and is quite distinctive even without the flowers.
Linaria purpurea - Purple Toadflax
This has the flowers in longer spikes than the yellow L. vulgare and tends to be more branched. In Lanarkshire it is an established garden escape.
Cymbalaria is a different genus which grows mainly on walls.
Cymbalaria muralis - Ivy-leaved Toadflax
The common plant of old walls is distinctive and can usually be found in flower all year. It is trailing, hairless and often with a purplish tinge. The flowers are lilac with yellow or white palate. However there are white forms.
Cymbalaria pallida - Italian Toadflax
This has shortly-haired stems with similar flowers to Cymbalaria muralis but they are larger.
Chaenorhinum minus - Small Toadflax is a tiny plant often growing in gravel and easily overlooked.