Identification notes
Reboulia is usually a straightforward species to identify, but difficulties may arise when thalli without receptacles (the distinctive umbrella, cup or button-like structures bearing the reproductive organs) are found. How do you confirm it from the thallus characters? Reboulia is sometimes confused with Marchantia (Preissia) quadrata and even with forms of Lunularia cruciata lacking its usual half-moon gemmae-cups. All three species have air pores on the upper surface of the thallus.
Allow the plants to dry and the differences will be easier to see. The surface of Reboulia then appears almost smooth and the air pores are very hard to see. In dry M. quadrata the pores are clearly visible with a hand-lens, like small pimples. Under the microscope, these are usually cross-shaped. Lunularia is easier because the thallus surface has areolae around each pore (making a snakeskin-like pattern on the surface, also characteristic of Conocephalum), something lacking in Reboulia and M. quadrata. However, when Lunularia is dry, the areolae are barely visible.
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