The hygroscopic structure present in Marchantia for spore dispersal is called the elaters.

Explanation:
Elaters are specialized structures found in the sporophyte generation of certain bryophytes, including Marchantia. They play a crucial role in the dispersal of spores.

In Marchantia, the elaters are elongated, ribbon-like structures that are attached to the spore capsules. Each spore capsule contains several spores and is surrounded by a protective covering called the calyptra. Inside the capsule, the spores are held together by a central columella.

When the spores are mature and ready for dispersal, the capsule dries out. This drying process causes the elaters to contract and twist. Elaters have specialized cells with helical thickenings in their walls, which give them the ability to change shape in response to moisture levels.

As the elaters twist and coil, they create a mechanical force that helps in spore dispersal. When the surrounding environment becomes humid, such as after rainfall, the elaters absorb moisture and expand. This expansion causes the twisting and coiling elaters to straighten out suddenly, releasing the spores with force. The spores are then dispersed into the air or onto nearby surfaces.

The hygroscopic behaviour of the elaters ensures that spore dispersal occurs under favourable conditions, maximizing the chances of spore survival and colonization in suitable habitats.