Why are thorns important to plants

Kariyat does not disagree. Moles noted that the results are consistent with paleontological evidence that spines evolved before large herbivores. The results highlight a tricky issue in the study of evolution and adaptation: Because of exaptation, understanding the current function of a trait is very different from inferring the evolutionary pressures under which it initially evolved.

Indeed, hypotheses about the original purpose of plant spines range far beyond the deterrence of herbivores of various sizes. Or that they first helped plants to sprawl and climb. This time-lapse video observes tobacco hornworm caterpillars feeding on two S. The plant on the left is intact; the plant on the right has had its spines cut off. The leaves of the left-hand plant survive longer because the spines restrict the movement of the caterpillars.

Rupesh R. Kariyat, Sean B. Hardison, Consuelo M. De Moraes, Mark C. Despite the number of credible alternatives, however, research into explanations for spinescence other than deterrence of mammals has been scant.

Perhaps that is because a highly influential and widely cited study examining the possible role of plant spines in insect herbivory was published in ; the authors found that removing the spines from holly leaves had no effect on caterpillar feeding. An irony is that the same study also questioned the value of those spines in deterring mammalian herbivores, because in feeding trials the animals failed to show a preference for spineless leaves. Although his own work focused on caterpillars, he noted that many other small herbivores, such as snails, could also be affected by spines and might have influenced their evolution.

Get highlights of the most important news delivered to your email inbox. Quanta Magazine moderates comments to facilitate an informed, substantive, civil conversation. Abusive, profane, self-promotional, misleading, incoherent or off-topic comments will be rejected.

In addition to offering protection from herbivores, it reduces water loss, which is important for surviving severely dry terrain like deserts. Cacti and many succulents feature this modification. While photosynthesis— the process plants use to make the sugar they need to fuel their daily lives— usually takes place in the leaves, cacti are able to keep on trucking by using their stem tissue instead. Some plants have modified their leaves to have spines only at the edges, which is what you see when examining a holly leaf.

An honorable mention goes to trichomes, which are hair-like projections arising from various plant tissue. These also can make plants less palatable to herbivores, but also add the ability for plants to pick up sensory cues from the environment. When landscaping with thorny plants, most are planted best in the background, out of the way of pets, where they could be daily hazards. That being said, they can work wonders for security, and oftentimes people will plant them underneath windows or along property borders to dissuade unwanted guests.

When planting or maintaining, make sure to wear protective gear, including long pants, closed-toed shoes, and thick gloves. Be sure to keep them trimmed at a reasonable height and width to ensure they stay garden-friendly and to keep flowers going all season long. They are neither a modified stem, nor a modified leaf. A close look reveals that they are hollow with no internal architecture that is characteristic of a leaf or stem. These prickles also occur in pairs beneath the calyx, which are the leafy structures under purple petals.

Not all prickles are hollow, such as the prickles that easily pop off on a rose bush, but these are. Skip to main content. The stem of Alluaudia ascendens , in the Desert Garden, showing multiple sharp thorns.

This species makes up a core component of the spiny thicket forests in southern Madagascar. Photo by Sean Lahmeyer.

Cross section of an Alluaudia ascendens thorn, with the addition of methylene blue dye for contrast. The internal anatomy matches that of a stem. The stem of Ceiba insignis silk floss tree , in the Desert Garden, showing bark with prickles. Cross section of a prickle from a Ceiba insignis silk floss tree. The entire structure is made up of rigid dermal tissue and is devoid of any characteristics of a leaf, stem, or root.

The stem of a tropical palm, Cryosophila albida , showing root spines along its trunk. Cross section of a Cryosophila albida root spine, with the addition of methylene blue dye for contrast. The internal anatomy matches that of a root, not a stem. Related Posts. A Fruitful Perspective. Soon after Henry E. Huntington purchased the San Marino Ranch formerly owned by James DeBarth Shorb in , he learned that many agricultural crops—such as avocados, peaches, and nuts—could be grown Bless This House.

A Rose for Our Times. Experts on nomenclature—from Madison Avenue marketing executives to the parents of newborn babies—have long believed that choosing the right name can make all the difference Comments Barbara A. You could also showcase the beauty of the aloe trunks and the visuals of the aloe head patterns.

Thank you, Sean. Wonderful article and photography, and love the cross-sections! Sean: Is the spine on Caesalpinia cacalaco a prickle?

Looking for which succulents prefer some amount of shade. Jim: The spiny projections throughout the plant body on Solanum pyracanthos are actually prickles, which are modified projections from the epidermis.