I read in my book that thorns are a kind of deformed side branches and spines are leaves. So a rose has thorns and a hawthorn has thorns. Now I also read that cacti has no leaves and therefore has thorns ???
Is this correct or are they spikes?
The handbook is explo 1 natural sciences ASO
Asker: Andrew, 30 years old
Answer
Dear Andy,
Apparently your manual is wrong.
Thorns have a slightly broader meaning: these are entire organs that have been transformed into something that pricks. So not only branches but also leaves or parts of leaves and roots can form thorns. We then speak of branch thorns (e.g. hawthorn, Citrus), leaf thorns (e.g. Asparagus, Cactus) or root thorns (e.g. thorn palm).
Spines are only formed from the epidermis, so that they can easily break off and are irregularly placed on the plant (eg the rose, blackberry).
In Cacti, the leaves of the short shoots (side branches whose leaves are very close together) have been transformed into thorns. We can interpret the groups of thorns as side branches because in the primitive Cacti (eg Pereskia) the leaves of the main stem do develop normally and the axillary bud grows into a short shoot with thorns.
Answered by
drs. Marc Reynders
Biology, systematics and evolution of seed plants. Specialized in tropical Cyperaceae.
university of Ghent
http://www.ugent.be
.