BIOL 1902 Lecture Notes - Evolutionary Arms Race, Automimicry, Verbascum
21 Mar 2014
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For 400 million years plants have been under attack from animals. Like an evolutionary arms race or ecological chess game, animals on offensive, plants on defensive: physical defences. Prickles are epidermal outgrowths: rose stems have prickles, raspberries and blackberries too. Thorns are modified branches; honey locust trunks and hawthorn branches have thorns. Spines are modified leaves on a thistle; most spines are dead with highly lignified cells (sclereids); thistles have spines. Sometimes these are aposematically coloured; automimicry might explain why rose buds look like prickles: trichomes: small hooked or clubbed hairs = dense tangles impede small animals such as mites and small insects. Some trichomes release sticky glandular secretions = glandular hairs or glandular trichomes. One type - separately stored phenols and enzymes, when animal brushes them they break open, contents mix like epoxy, create chemicals that repel; stinging nettles produce painful trichomes that inject chemicals glue-like ooze that hardens.
