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Friday, December 7, 2012

Family Profile: The Cactaceae

By Jennifer Hoffman and Chelsea Warner

Figure 1: Opuntia corallicola, semaphore pricklypear.
Photo credit: T. Ann Williams.
This post is one of a series from professor Nisse Goldberg's Plant Taxonomy students at Jacksonville University. FNPS blogger Laurie Sheldon assisted the students with their initial drafts, providing suggestions for editing and content development.


Classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Order: Caryophyllales
Family: Cactaceae



Features
Leaves: typically reduced as spines
Fruit: berry
Flower: zygomorphic or actinomorphic, with tepals rather than sepals and petals


Figure 2: The specific epithet of Harrisia fragrans  may
allude to its sweet smelling flowers.
Photo credit: Keith Bradley.
Description
The cactus plant family or Cactaceae is specially adapted to survive in hot and dry conditions. For example, many species have sharp spines to protect them from predation, direct rain runoff towards their root system, and reduce internal heat loading by reflecting light away from the plant (Fig. 1). In addition, the dermal cells are thick-walled and lined with a cuticle or waxy layer. The cuticle helps the plant retain water and to reflect light, thereby reducing internal temperatures.

Figure 3: Lophophora williamsii has no spines .
Photo credit: Kauderwelsch
 Photosynthesis, the production of sugars, commonly occurs in the leaves of most plants. As the majority of species in the cactus family have reduced leaves, they conduct photosynthesis primarily along their stems or areoles. These shoots are also where the cactus retains its water, expanding and contracting to accommodate the changing quantities of water being absorbed from the roots.

The root system of the cactus remains relatively close to the surface while extending out up to 15 meters! During heavy amounts of precipitation, the roots will begin to grow new root extending from the previous roots to increase water absorption. During times of drought the roots will begin to shrivel and deteriorate creating an air gap that can help trap water.

There are 23 species of Cactaceae in Florida, 12 of which are native. Among the native species, 7 are listed by the state as endangered. Examples of these include Opuntia corrallicola, semaphore pricklypear, and Harrisia fragrans, Caribbean applecactus (Figs. 1 and 2). Found in Texas, Peyote or Lophophora williamsii is known for psychoactive effects (Fig. 3).

References
Judd, WS, Campbell, SC, Kellogg, EA, Stevens, PF, and Donoghue, ML. 2008. Plant systematics: A phylogenetic approach. Sinauer Associates, Inc. Massachusetts, USA
http://florida.plantatlas.usf.edu/
http://plants.usda.gov/java/ClassificationServlet?source=display&classid=Cactaceae
http://www.enchantedlearning.com/subjects/plants/types/cactus/
http://www.cactusmuseum.com/survival.asp

Image sources
Figure 1: http://www.florida.plantatlas.usf.edu/plantimage/Opuntia_corallicola2.jpg
Figure 2: http://www.florida.plantatlas.usf.edu/plantimage/Harrisia_fragrans6.jpg
Figure 3: http://upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Lophophorawilliamsii.jpg/320px-Lophophorawilliamsii.jpg

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