Lithophyte

Lithophytes are plants that grow in or on rocks. They can be classified as either epilithic (or epipetric) or endolithic; epilithic lithophytes grow on the surfaces of rocks, while endolithic lithophytes grow in the crevices of rocks (and are also referred to as chasmophytes). Lithophytes can also be classified as being either obligate or facultative. Obligate lithophytes grow solely on rocks, while facultative lithophytes will grow partially on a rock and on another substrate simultaneously. Lithophytes that grow on land feed off nutrients from rain water and nearby decaying plants, including their own dead tissue. It is easier for Chasmophytes to acquire nutrients because they grow in fissures in rocks where soil or organic matter has accumulated. For most Lithophytes, nitrogen is only available through interactions with the atmosphere. The most readily available form of nitrogen in the atmosphere is the gaseous state of ammonia (NH3). Lithophytes consume atmospheric ammonia through a concentration gradient that allows the compound to traverse the plants' apoplast. Once free in the apoplast, gaseous ammonia is absorbed into metabolic cells by the enzyme glutamine synthetase. To be able to absorb the few nutrients available on rocks or rocky substrates efficiently, Lithophytes have evolved certain adaptations. They possess decreased numbers of root hairs and larger root diameters in comparison to other plant species. To add to this nutrient uptake efficiency, lithophytic plants have increased their relationship with arbuscular mycorrhizal fungi and dark septate endophyte fungi. These two types of fungi live inter- and intracellularly with the roots of Lithophytes and a wide variety of other plant species. They increase the uptake of nutrients and water and have been found in greater concentrations in Lithophytes. Walls, and other exposed stonework, are colonised by plants in a similar way to the colonisation of cliffs and scree. These natural features are uncommon, especially in the lowlands, so walls are important for the conservation of plants which might otherwise be very isolated.