Hygroscopic roots are found in epiphytes (plants which live on other plants for space). They hang in the air and possess velamen or spongy tissue for absorbing moisture directly from atmosphere. The epiphytic roots are devoid of root hair and root cap, eg, Orchids, Vanda, Dendrobium.
Bryophyllum has epiphyllous/foliar roots. These roots develop from leaves, especially the injured plants.
In Rhizophora, prop roots are present. They are pillar like roots, which give support to the plant. In Rhizophora, prop roots possess lenticels for aeration.