Arachnoid organs, such as leaves or stems, have an external appearance similar to
cobwebs – the appearance of being covered with fine, white, usually tangled hairs. This can cause plants to appear grey or white.[1] The arachnoid appearance is common on the leaves and stems of various
sclerophyllous members of the family
Asteraceae, such as some
thistles. The arachnoid appearance of Haworthia arachnoidea arises from the
spinescent leaf denticles, and the arachnoid appearance of the cactus Cephalocereus senilis is from long-lasting hairy spines.