This section is from the book "Sub-Alpine Plants Or Flowers Of The Swiss Woods And Meadows", by H. Stuart Thompson. Also available from Amazon: Sub-Alpine Plants: Or, Flowers of the Swiss Woods and Meadows.
Flowers minute, hermaphrodite, solitary and axillary or in cymes. Calyx 3-5 lobed, persistent. Stamens 3-5, attached to the calyx. Ovary 1-celled. Fruit a 1-celled, 1-seeded achene. Leaves narrow, entire, without stipules. Slender herbs parasitic on roots, of which there are about 100 in the ancient world and in Brazil.
Stem prostrate, branching on one side only, leafy from the base upwards. Calyx rolled up at the tip after flowering, as long as or longer than the fruit. Middle bract much longer than the two lateral ones.
Dry pastures and stony places in the Alps and sub-Alps up to 7500 feet.
Eastern, Central, and Western Alps; Western and Northern Asia.
There are 3 or 4 more species of Thesium found in the Alps, including the British T. humifusum DC. They are all difficult to determine, especially without ripe fruit.