Thesium is a genus of shrubs and herbs parasitising partly (hemiparasites) or fully (holoparasites) upon the roots of plants growing around them; partly, because they also photosynthesise, but not enough for their growth needs. The plants are usually glabrous, i.e. hairless.

Thesium leaves are alternate, varying in shape from linear, narrowly lance-shaped, awl-shaped, scale-like or nearly round. The bisexual flowers grow axillary or terminal in racemes, spikes or panicles. The five-lobed perianths are tubular or cup-shaped. There are five stamens growing from the insides of the perianth lobes. The anthers are oblong or ovoid. The ovary has three segments. The style is cylindrical, its stigma three-lobed or capitate, i.e. shaped like a head or dense cluster. The fruit is a roundish nut, usually ten-ribbed and the perianth persistent.

The photo shows a Thesium plant in the Kogelberg flowering in November. Its five-pointed, white star flowers grow in stem tip clusters, the buds creamy yellow, surrounded by fleshy orange sepals. The leaves are tiny and sparse.

The plant may be Thesium strictum, the rootthug or in Afrikaans teringbos (tuberculosis bush). That plant is found on sandstone slopes from Namaqualand to Grahamstown (Privett and Lutzeyer, 2010; Leistner, (Ed.), 2000; Bond and Goldblatt, 1984).