I realise this is a forum for UK wild life but I cannot find anywhere else to get help with these plants. If someone can partially identify the plants - maybe just the family - that would be a help.
These plants were found on the margins of a reservoir near Madrid. They or their seeds spend a lot of time submerged (when the reservoir is full) and then a lot of time in semi-desert conditions on sandy soil. I found about 4 very similar species, differing mainly in the colour of their sepals (red and white in the attached photos). The ruler is a cm/mm ruler so you can see the closed flowers are less than 1mm and the open flowers are about 1.5mm.
The flowers have 5 petals and 5 stamens (or 5 pairs of stamens it's very hard to tell). The leaves are succulent but not hairy.
your plant is actually also a British native, although admittedly an extremely rare one! It is Corrigiola littoralis L. - the Shoreweed (Caryophyllaceae). It is naturally found on lake margins, but also sometimes on railway track ballast - its only recent British native locality at on spot on the shore at Slapton Ley on the S. Devon coast. It is more widely distributed elsewhere in Europe.
Thanks for this. I see there is research being done in the UK on the habitat of this plant in order to conserve this rare plant (rare in UK). If any researcher wants to know of the site where I found a plentiful supply of these plants they may contact me. I note that this is also know as Strapwort.