Why thorns

I would like to see some photography showing the desert garden plants as a landscape: groupings, on the slopes, cacti in groups, and the backgrounds of yucca and aloe. You could do more to encourage the plantings of the cactus and aloe and yucca that could become, gasp, a fad for waterwise homeowners.

Sandra Mader on Jul 22, - pm said:. Thanks, Sean. Great info to demonstrate in Adaptations in a Changing World. Now all we need is to be able to reunite the students and docents! Deborah Shaw on Jul 27, - pm said:. Hi Sherm: Yes, the spine on Caesalpinia cacalaco is actually a prickle, just like on a rose bush.

Susan LaFreniere on Aug 01, - pm said:. Jim Wehtje on Aug 04, - pm said:. So, in Solanum pyracanthos porcupine tomato , the exact same looking orange spinous projections are spines when coming out of the middle of the leaves, but thorns when coming out of the stem? Or are the ones coming out of the stem also possibly modified leaves leaf tissue? The spiny projections throughout the plant body on Solanum pyracanthos are actually prickles, which are modified projections from the epidermis.

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. Then they went a step further by manipulating the spine density, slicing away spines with a razor blade so that all the plants had the same number, and repeated the experiment.

Lastly, they expanded the research to include two other species in the same genus: S. The three species vary in spine density: Ethiopian nightshade has the fewest, while the purple devil has the most. If caterpillars fell off the plants during the process, the researchers put them back on an unfinished leaf and allowed them to continue feeding. Kariyat, Mescher and their colleagues found the same pattern across all three trials: Spines were always an impediment to the hungry larvae.

With the prickles cut, caterpillars more quickly reached the leaves they desired. For intact plants, the species with the most spines — the purple devil — proved most difficult for the caterpillars to defoliate. Moreover, the spines not only slowed the caterpillars but also interfered with their footing and forced them into more acrobatic maneuvers. As a result, the caterpillars frequently fell off while traveling between leafy shoots.

Sometimes they even impaled themselves on the larger spines. Nevertheless, the team does not insist that their results prove insects were the primary reason that plants developed spines, prickles and thorns. The caterpillars, which were largely unaffected by the alkaloids, became specialists at preying on the plants. The unexpected results were a bit hard for others in the field to swallow.

Others are less convinced. He and William Bond , emeritus professor at the University of Cape Town in South Africa, used phylogenetic methods to show in that the diversity of spiny plants in Africa coincided with an uptick in bovid mammals, such as wildebeests and gazelles. That finding supports the traditional view that spines defend against large mammals. 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.

Other plants, including cacti, have spines , another type of sharp, pointy weaponry that forms instead of leaves. Thorns arise from shoots in plants such as bougainvillea, hawthorn and citrus.

Irish, who is also professor of ecology and evolutionary biology, was fascinated by thorns that grow on old honey locust trees, commonly found along the streets of New Haven and other urban areas. While most honey locusts have been bred so that they no longer have thorns, some older trees with dangerous, foot-long thorns still exist.

As a plant scientist, she was intrigued by how these structures arose, but she put off investigating the question for decades. As it happens, she is also an expert on stem cells.