arachnoid (botany)
{{Short description|Botanical term}}
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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.{{Cite book | last = Jackson | first = Benjamin Daydon | author-link = Benjamin Daydon Jackson | date = 1928 | title = A Glossary of Botanic Terms with their Derivation and Accent | url = https://archive.org/details/glossaryofbotani1928jack | publisher = Gerald Duckworth & Co. | location = London | edition = 4th | language = en | access-date = 27 December 2022 | via = Biodiversity Heritage Library }} 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.
{{Gallery
| File:Eriocephalus africanus IMG 5720.JPG
| alt1=refer to caption
| Eriocephalus africanus, showing lightly arachnoid leaves and heavily arachnoid seed follicles
| File:Arachnoid leaves of unidentified Gazania 2012 07 05 7252s.JPG
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|The arachnoid leaves of this Gazania are covered with a fragile cobwebby felt.
| File:Haworthia arachnoidea - cobweb aloe.jpg
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| Haworthia arachnoidea, the cobweb aloe, has a spidery appearance.
| File:Cephalocereus senilis.jpg
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| Cephalocereus senilis has an arachnoid effect created by modified spines.
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