Rubra means reddish. A rubra plant is a reddish form of a plant.
Science did not describe any rubra yet. Dyckias species have in most cases a rubra form.
The important is to observe that rubra plants do not get greenish any time. Rubra is not a temporary condition. Dyckias may get reddish when the sun is at plenty and the water is lacking. This is a phenomenon provoked by dryness and insolation. It is a defense attitude of the plant, a way the plant has to cope with this harsh situation.
Rubra is definitive and not a transitory or temporary mood it is not a phase.
Some extremely silver plants will show their rubra form just when wet
like the case here. Otherwise it may be difficult to distinguish a rubra Silvery form from a normal plant. In many cases it is impossible to tell a rubra form apart from a reddished suffering plant.