When Plants Attack II: Conventional Weaponry
21.08.2023 - 11:57
/ theunconventionalgardener.com
/ Emma Doughty
“Every rose has its thorns”, or so the song goes. Except, it’s not true, as we shall see in a minute.
Thorns are part of a plant’s conventional weaponry, defensive structures designed to protect their tasty parts from those pesky herbivores who want to eat them. Botanists call plants that are spiny spinescent, which I think is a lovely word, although of course the spines themselves can be owie.
Botanists have three different categories for spiny growths, dividing them up by the part of the plant from which they have been formed. So thorns are modified, short branches that grow from axillary buds. You can see them on hawthorn and blackthorn (sloes), among other things. The Holy Thorn at Glastonbury is an unusual variety of Hawthorn, Crataegus monogyna ‘Biflora’, which flowers twice a year.
Spines, on the other hand, are formed from modified leaves or leaf parts. Cacti have spines – the fleshy green bits are stems, and their leaves have transformed into spines. Not only do they protect their precious water supplies from hungry animals, but spines lose less water in the desert heat than leaves would; it’s a dual-purpose adaptation.
Apparently the prickly bits at the edges of holly leaves are also spines. They’re called marginal spines and are extensions of the major veins in the leaf. It’s always fascinating to see how plants have achieved the same end via different means. That’s evolution, that is
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