The small leathery leaves, tightly pressed to the stems in this species, are adaptations to the harsh arid conditions in which it occurs. The Arid Protea Fynbos vegetation in which P. appressum is restricted, receives a fairly low annual rainfall (300–400 mm) and extreme seasonal temperatures, from cold conditions in winter to very hot conditions throughout summer (Vlok & Schutte-Vlok 2010).

The fruit of Phymaspermum have stalked glands between the ribs which rupture when they come into contact with water, to release a sticky gelatinous substance that possibly helps to glue the fruit to the soil (Källersjö 1986; Ruiters et al. 2016). Phymaspermum is the only genus within the tribe Anthemideae that have these stalked glands on the fruit (although this character has been lost in 2 of the summer rainfall species, P. acerosum and P. pinnatifidum).