Thesium

Rootthugs

Thesium is a of hemiparasitic flowering plants in the Santalaceae, with approximately 325 distributed primarily across Africa, Europe, and Asia. The genus is particularly diverse in South Africa, where roughly half of all species occur. Species in this genus are root hemiparasites that form haustorial connections to roots. The genus has undergone taxonomic revision, with several segregate genera (Austroamericium, Chrysothesium, Kunkeliella, Thesidium) now subsumed within Thesium.

Thesium by (c) Eleftherios Katsillis, some rights reserved (CC BY), uploaded by Eleftherios Katsillis. Used under a CC-BY license.

Pronunciation

How to pronounce Thesium: /ˈθiːziəm/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Images

Habitat

Thesium occupy grassland and open vegetation , including forest-steppe and meadow . Specific habitat requirements vary by species; some occur in peri-Carpathian forest-steppe vegetation, while others inhabit alpine or subalpine zones in the Himalayas. In Lithuania, T. ramosum was found in association with Fabaceae species, with negative correlation to Poaceae coverage.

Distribution

The has a wide distribution across the Old World, with centers of diversity in South Africa (approximately 50% of ), the Mediterranean region, and temperate Eurasia extending to western China. Specific species distributions include: T. ebracteatum in central and eastern Europe (including a relict in Romania); T. ramosum to western Europe through western China, with populations in North America (Alberta, three western US states) and Lithuania; T. jarmilae in the Sikkim Himalaya; and Canarian in T. sect. Kunkeliella (including T. palmense on La Palma).

Ecological Role

As root hemiparasites, Thesium form haustorial connections to roots, extracting water and nutrients while maintaining photosynthetic capacity. The relationship with host plants shows selectivity patterns that vary among species. In some , Thesium species serve as indicators of undisturbed grassland and relict vegetation.

Human Relevance

Several Thesium have significance: T. ebracteatum is listed in Annex II of the EU Directive and appears on national Red Lists across Europe; T. palmense and other Canarian in T. sect. Kunkeliella are subject to in situ and ex situ conservation efforts; T. ramosum is regulated by the USDA in the United States due to potential and has established in Alberta, Canada. T. chinense is used in traditional Chinese medicine.

Similar Taxa

ComandraShares Santalaceae (or Comandraceae) and hemiparasitic habit; differs in determinate growth and unbranched stems versus indeterminate, branched aerial stems in Thesium
GeocaulonRelated in North America with similar hemiparasitic habit; distinguished by determinate growth and unbranched habit compared to Thesium ramosum

More Details

Taxonomic History

The has been subject to significant taxonomic revision. Nickrent and colleagues have argued that Austroamericium, Chrysothesium, Kunkeliella, and Thesidium should be treated as synonyms of Thesium. Thesiaceae is sometimes recognized as a separate , though most sources place Thesium in Santalaceae.

Conservation Status

One in T. sect. Kunkeliella is already considered extinct. The section represents Canarian with restricted distributions and high threat levels.