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Prickles on a blackberry branch. In plant morphology, thorns, spines, and prickles, and in general spinose structures (sometimes called spinose teeth or spinose apical processes), are hard, rigid extensions or modifications of leaves, roots, stems, or buds with sharp, stiff ends, and generally serve the same function: physically defending plants against herbivory.
The spines are the relatively large, radiating organs; the glochids are the fine prickles in the centres of the bunches. Glochids ( Opuntia microdasys monstrose ) Glochids or glochidia ( sg. : "glochidium") are hair-like spines or short prickles, generally barbed, found on the areoles of cacti in the sub-family Opuntioideae .
Prickles and thorns are an evolved defense against herbivores — animals that eat plants — and can also aid in growth, plant competition and water retention, according to the study.
The homology of leaves is an easy conclusion to make. The plant morphologist goes further, and discovers that the spines of cactus also share the same basic structure and development as leaves in other plants, and therefore cactus spines are homologous to leaves as well.
For example, the article says that spines are derived from leaves, but none of the four sources I listed at User:Peter coxhead/Work page#Spines vs. thorns restrict the term to leaf-derived structures. Also, the use of spinosus as an epithet is relevant; many plants with such names have what the article calls "thorns", e.g. Prunus spinosa.
The terms emergences or prickles refer to outgrowths that involve more than the epidermis. This distinction is not always easily applied (see Wait-a-minute tree ). Also, there are nontrichomatous epidermal cells that protrude from the surface, such as root hairs .
A plant's leaves and stem may be covered with sharp prickles, spines, thorns or trichomes- hairs on the leaf often with barbs, sometimes containing irritants or poisons. Plant structural features such as spines, thorns and awns reduce feeding by large ungulate herbivores (e.g. kudu , impala , and goats ) by restricting the herbivores' feeding ...
In many cases, spines are a defense mechanism that help protect the animal against potential predators. Because spines are sharp, they can puncture skin and inflict pain and damage which may cause the predator to avoid that species from that point on. The spine of some animals are capable of injecting venom. In the case of some large species of ...