Why do cactus have needles

The spines of this Ferocactus occur in two sizes and they do not appear to be located in phyllotactic spirals. Spines that act as extra-floral nectaries in cacti. Other aspects of spine biology are complex and in need of study. In several genera, some spines in each axillary bud develop as glands, known as extrafloral nectaries.

They secrete a sugar solution that attract ants. These spines consist of loosely arranged parenchyma cells that secrete into intercellular spaces, and the accumulating nectar is then forced upward and out through small holes in the epidermis. Such spines are short and broad but still have a spine-like organization with the secretory cells looking like short, broad, thin-walled fibers.

The axillary buds of Coryphantha clavata are unusual -- the bud's apical meristem becomes extremely elongate, and the portion at the tip of the tubercle forms spines, the portion in the middle of the tubercle forms glands modified spines , and the basal portion produces flowers not shown here. Mauseth, J. Development and ultrastructure of extrafloral nectaries in Ancistrocactus scheeri Cactaceae. Botanical Gazette — Spines that provide shade in addition to or instead of protection.

Many cacti are protected from full sunlight by a dense covering of spines. Such plants would be killed quickly by exposure to full sunlight in Phoenix, Arizona. Species in such cool or semi-shady habitats often have either just a few spines or only very short ones. However, cacti from intensely sunny, hot deserts often must have a complete covering of spines. In many cases, the spines are so strong and painful that they obviously offer both protection and shade, but in many species the spines are so soft that a hungry, thirsty animal would chew through them with no trouble.

The benefit of such spines definitely appears to be blocking sunlight and thus preventing the plant from over heating, the chlorophyll from being bleached and the plant's DNA from being damaged. For example, in Mammillaria plumosa , spine epidermis cells project outward as long trichomes, giving the spine a feathery appearance.

In other species, the spines are flat, thin and papery, being too flexible to deter animals, but broad enough to shade the plant as well as to camouflage the cacti among the grasses with which it grows. Matucana aurantiaca grows in such humid, foggy areas that keeping ahead of mosses is a challenge.

Oroya peruviana yellow growing with Austrocylindropuntia tephrocactoides at high, cool altitude. The body of Epithelantha bokei is heavily shaded by its spines, but the spines are so soft they would not deter an animal from eating the cactus. Epidermis cells on spines of Mammillaria plumosa grow out as trichomes, shading the plant. Teddy bear cholla Opuntia bigelovii.

Spines of the Cholla are specialized to detach and attach onto anything that comes to close. There are tiny barbs at the tips which grab on to anything that gets too close. When hiking in the desert, it is easy to get them stuck on your shoes.

I usually grab a rock and use it to push off the Cholla segment. When all else fails, a good pair of needle-nose pliers works. Two young saguaro cactuses are emerging from the shelter of a creosote shrub. Hopefully, you have a new appreciation for cacti and their spines. What Plant Where? Beautiful Plant Combinations.

These cactus are so beautiful to look at, especially those with brightly coloured flowers. It is hard for me to imagine the spines as being actually leaves.

I always tend to think of them as thorns instead. Just like a pine tree has the needles, the cactus has the spines? They are the "leaves? Next time I see a cactcus, I will remember this! Thanks, Noelle. Wonderful post!! The consciousness of plants never ceases to amaze me… a plant must protect itself and also bring in moisture… love the photos of the handsome as well as prickly creatures… beautiful flowers.

Most interesting post. I didn't know all that. Some cacti are so beautiful with their otherworldly shapes. They are unusual creations. Beautiful photos and descriptions, Noelle! Your plants look so exotic to my northern eyes… Janice. Loved your post! So all in all, spines are adaptations that protect and help cacti hide from animals that may want to eat them. They also provide shade for the plant, which keeps them cooler and limits water loss.

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