Plants are constantly fighting a battle against critters that want to eat them. We see the result of this battle in the physical defences that plants have evolved over time. Plants use many different types of defence mechanisms; from tough waxy armour to chemical-laden barbs. These defences may do as little as discouraging an enemy from chowing down on the plant, or as much as causing an enemies’ long and painful death. Whatever it takes to avoid being someone’s dinner. In this Ecological Explainer, I’m focusing on those spiky plant parts that we see quite often..that all of us have probably hurt ourselves on at some point.
In botany, we class spiky plant parts into 3 major types:
Thorns are sharp and pointed branches.
They have vascular tissue, and so some will be green telling us they are able to photosynthesise. They can be branched and can have leaves.
Spines are modified leaves or parts of leaves.
They don’t have vascular tissue and don’t photosynthesise, and tend to be hard and dry. Spines can develop from: the little stem that holds the leaf (petiole); the main cluster of veins in the leaves (midrib); other smaller veins; or the stipule.
Prickles are spiky outgrowths from the bark of a plant.
They are usually small, and grow from the cortex and epidermis layers of the bark. These layers don’t have vascular tissue, so prickles don’t either.
In summary, the three main forms of spiky things found on plants are:
- thorns (spiky stems)
- spines (spiky leaves and leaf bits)
- prickles (spiky outgrowths of the bark).
There are some other pricks and piercers like modified roots and trichomes, but I’ll save them for another post.
Armstrong, W.P. (2007) Botany 115 Vegetative Terminology: Modified Roots, Stems and Leaves. Wayne’s Word: Online Textbook of Natural History, accessed Feb 2018 <http://waynesword.palomar.edu/ecoph30a.htm>
Biology Online Directory (2017), Areole, accessed Feb 2018 <https://www.biology-online.org/dictionary/Areole>
Raven, P., Evert, E., Eichhorn, S. (1986) Biology of Plants, Fourth Edition. Worth Publishers: New York.
Missouri Botanical Gardens (2017), Pereskia grandifolia var. grandifolia, accessed Feb 2018 <http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=273816&isprofile=0&=>