This very troublesome, annual weed is dynamic after autumn and winter rains. It is an erect, sprawling or decumbent herb growing up to 50cm high that is covered with rather stiff star-like (stellate) hairs and is woody at the stem. It occurs on all soil types; most common in waste places, in sheep yards, around farm buildings, closed yards, watercourses and roadsides.
The leaves are circular and 8-10cm in diameter resembling those of a geranium. The base of the leaf is cordate (heart shaped with a notch at the base), margins are crenate (a margin with shallow, rounded teeth). The leaves are palmately veined with 5-7 short triangular lobes. The petiole (leaf stalk) is mostly 1.5-12cm long and rarely 20cm.
The flowers have 5 petals that are about 4-6mm long, white or pink in colour, and twisted in the bud. The pedicel (flower stalk) is generally less than 1cm in length at maturity. The fruit is a schizocarp (a dry fruit which splits into individual carpels). The schizocarp is disc-shaped surrounded by the calyx (sepals of the flower) and brown when ripe.
The strong tap root is not easily pulled out and this root system enables the weed to survive very harsh conditions. It is extremely hard-seeded and the dropped seeds can germinate sporadically over many years. It has been discovered that the pesticide methyl bromide breaks down the hard-seededness, causing mass germination!
The seeds also pass through the digestive tract of animals and are therefore often introduced into ‘new’ lands via manure. It can be toxic to cattle though.
The sectioned fruit (schizocarp) looks like a sliced wheel of cheese, hence the common name of cheeseweed mallow.