Rebutia muscula is a clumping cactus that form low cushion covered up to 6 inches (15 cm). It grows quite close to the ground and offsets only with age. The stem is hemispherical, later elongated, pale green, up to 1.6 inches (4 cm) wide and tall. The stems of this cactus grow usually taller than they are broad. It would appear that in cultivation they grow larger and cluster more vigorously than in habitat. The flowers are deep orange, funnel-shaped, up to 1.4 inches (3.5 cm) long, up to 1.2 inches (3 cm in) diameter, from the base of the stems. Flowers profusely throughout spring into summer with spurts of flowering into autumn.