Thalloidima

Thalloidima is a genus of lichen-forming fungi in the family Ramalinaceae. It has 13 species.

Taxonomy
The genus was originally circumscribed by Italian lichenologist Abramo Bartolommeo Massalongo in 1852. It was subsumed into genus Toninia by Einar Timdal in 1992. The genus was resurrected for use in 2018 by Kistenich and colleagues following a molecular phylogenetics-led restructuring of the Ramalinaceae.

Description
Thalloidima is defined by the distinctive grey pigment in the and  rim, which turns violet with K+ and N+ reactions, originally termed as "Thalloidima-grün" (equivalent to ). The thallus predominantly appears as flattened to. Two species in this genus are not lichenized. While many, if not all species, initiate their lifecycle as parasites on, some remain parasitic throughout. The generally range from ellipsoid to  shapes and are 1-septate, though some rare forms are  and 3-septate.

Species
, Species Fungorum (in the Catalogue of Life) include 13 species in Thalloidima:
 * Thalloidima albilabrum
 * Thalloidima arcticum – Holotype: Canada. Northwest Territories
 * Thalloidima candidum
 * Thalloidima collematicola – Holotype: Italy
 * Thalloidima ioen
 * Thalloidima leptogii Holotype: Italy
 * Thalloidima massatum – Holotype: USA
 * Thalloidima opuntioides – Neotype: France
 * Thalloidima physaroides – Holotype: Czech Republic
 * Thalloidima rosulatum
 * Thalloidima sedifolium – Neotype: Italy
 * Thalloidima subdiffractum – Holotype: USA
 * Thalloidima tauricum