Desert Botanical Garden: Lab Exercise Name: 1201 N Galvin Parkway, Phoenix dbg.org

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1 Desert Botanical Garden: Lab Exercise Name: 1201 N Galvin Parkway, Phoenix dbg.org Introduction (read this first)* - Bring Student ID. Confirmation # Desert biomes are defined by their low precipitation, less than 30 cm per year (12 inches). Temperatures vary between deserts, however, the lack of water exacerbates temperature fluctuations. Thus, desert temperatures tend toward extremes. The Sonoran Desert, which includes the Phoenix area, receives less than 25 cm of rain per year (10 inches). This precipitation is concentrated in two separate seasons: winter storms and the summer monsoons. Summer temperatures may exceed 48 0 C (118 0 F) with occasional overnight freezes in the winter. Many animals that live in this desert either migrate or aestivate (e.g. hibernate) at times of stress. Most plants, however, cannot migrate. [How can some plants migrate or disperse to avoid seasons of stress?] Plants that live in the desert have adapted to the xeric (dry) environment and the broad range in temperatures. This exercise will focus on the many adaptations found in desert plants. Throughout your visit search for examples of adaptations to gain water and prevent water loss. The last page of this handout provides a sheet to record these adaptations with examples. The success of desert plants in obtaining and storing water attracts animals that also need water. Thus, desert plants have evolved extraordinary structures to protect themselves from animals. We will concentrate on local plants, but will compare these examples to similar adaptations in plants from other deserts. Unrelated organisms with similar adaptations are examples of convergent evolution (the Garden signs refer to this phenomenon as Ecological Convergence). We will examine many examples of convergent evolution in the Succulent Gallery. The Cactaceae (cactus family) dominates the Sonoran flora (e.g. Saguaro cactus, Carnegiea gigantea). Along the Desert Discovery Trail and the Cactus Gallery you will see great diversity in the forms of these plants. Some species live in the tropical rainforests of South America and lack the typical cactus structures. Identify the variations of structure in these different forms, and the different parts that evolved for their roles, e.g. which parts are leaves? stems? roots? Throughout your tour, look for plants we will count at Thunderbird Park (Lab Manual Desert Ecology). You will need to identify these plants in next week s exercise. Summarize the variety of desert adaptations seen today on the last page. * To receive credit for this exercise, you must attach your receipt from the botanical garden. You may visit the garden anytime from Oct 1 Nov 10. Please call ahead to reserve a time: Confirmation # Cost: $5 with your Student ID. Assignment Due in Lab: March 22 or 24. Bio182 Botanical Garden 1

2 Plants to Identify for Transects This list includes plants named in your lab manual as likely organisms we will see at Thunderbird Park (next lab) and that you will see along the trail. Brittle bush - Encelia farinosa - Sunflower family [Asteraceae (Compositae)] Shrub with velvety leaves that have smooth edges. Velvety quality of leaf is due to hairs that provide shade. Stems are brittle and release resiny substance (resin can be chewed like gum - not bad!). Drought deciduous; most leaves fall when plant is water stressed, except for small, hairy leaves. New leaves after winter rains are larger & greener. Bursage - Ambrosia detoidea - Sunflower Family [Asteraceae (Compositae)] Shrub with rough-textured leaves with serrated (toothed) edges. Usually smaller in size than brittle bush. No resin on stem. Drought deciduous. Aromatic leaves, spiny fruits. Creosote Bush - Larrea tridentata - Caltrop Family [Sygophyllaceae] Large shrub with resiny, small leaves. Resin slows water loss and protects against UV radiation. Flower is yellow and fruit is white & fuzzy. Drops some leaves during drought. Sprouts new stems from base; center may die, with living stems forming an ever-widening ring. Distinctive oder; chemical compounds protect against herbivores, may also provide medicinal compounds. Paloverde - Cercidium spp. - Pea Family [Fabaceae (Leguminosae)] Several species of trees with greenish stems. Small, twig-like leaves. Stem responsible for most photosynthesis (3/4). Drought deciduous. Barrel Cactus - Ferrocactus spp. - Cactaceae Unbranched, barrel shaped (up to 10 feet tall). Flattened, curved, reddish spines. Jointed Stem Cacti - Opuntia spp. - Cactaceae All have stems able to break apart at joints and take root (clones). Teddy Bear Cholla - O. bigelovii One of the Jumping Chollas. Dense, golden spines; short roundish stems Cane Cholla - O. spinosior Stem joints are longer & thinner than Teddy Bear. Spines less dense. Prickly Pear - O. englemanii Flattened, plate-like stems; plates face sun during monsoon season. Bio182 Botanical Garden 2

3 Part I. Desert Discovery Trail The Desert Discovery Trail begins at the entrance of the garden and makes a long loop that returns you to the start. Follow this trail. Use the guide book to identify plants and to help answer the questions below. Please Do Not Write in the Book. Station 1. Arizona Queen of the Night What is the family of this species? Is it an Arizona native? Where is it found? This cactus, like most members of the family, lack leaves (except for spines, which are thought to be remnants of leaves encircling a growing point such as a bud). Most cacti use their stems for photosynthesis. Considering that water evaporates from all surfaces of a plant exposed to air, how might the absence of leaves help cacti live in the desert? Most cacti store water primarily in their stems. Where does this plant store its water? Is this a flowering plant? What pollinates this plant? At what time of day? Station 2. Creosote Bush This is one of the most abundant plants in our Sonoran Desert. Describe two structural features of this plant that may be adaptations for the desert. Describe how this species reproduces asexually. Does it also reproduce sexually? What is your evidence? Bio182 Botanical Garden 3

4 Station 3. Senita What is unusual about the spines on this species? Describe two ways in which these spines help the plant survive in the desert. Station 4. Totem Pole Cactus What is the scientific name of this species? Why does it have a different common name than the Senita? Apply the Morphological Species Concept to determine whether these two plants (Senita & Totem Pole Cactus) should be considered one or two species. Explain. Will these two types interbreed? How would you apply the Biological Species Concept to this problem? Station 5. Jojoba List three adaptations of the jojoba leaf to the desert environment. Based on your knowledge of plant reproduction, why are jojoba nuts found only on the females of this species? What part of the jojoba plant contains a useful oil? What is special about this oil? Bio182 Botanical Garden 4

5 Note the Century Plants and Aloes display between Stations 5 & 6 Station 6. Parry s Century Plant Name the family of this species: What is the geographic distribution of this family? What adaptive characteristics do agaves share with cacti? Is this an example of homology or convergent evolution (ecological convergence)? Explain. What is the advantage of having all its leaves in a tight cluster? Besides storing water in their leaves, can you think of any other leaf adaptations in this plant? Organisms that only reproduce once in a lifetime are known as semelparous. Organisms that breed more than once are called iteroparous. What advantage might there be to semelparity? Station 7. Aloe Name the family of this species: Which plant seen so far most resembles the aloe? Describe these similarities. Aloes are iteroparous. Based on this information, and the geographical information in your guide, do you think the similarities between aloes and agaves are due to common ancestry or convergent evolution? Explain. Bio182 Botanical Garden 5

6 Station 8. Ocotillo Note: may be off display at this location; there are other examples in the garden. Describe the meaning of drought deciduous. How is this an adaptation? What characteristics of the stems resemble cacti? How is this a desert adaptation? Station 9. Banana Yucca Examine this plant for desert adaptations. Station 10. Saguaro (see also page 11 of this worksheet) Why do saguaros have pleated stems? Compared to other cacti in the US, the saguaro is the. Note the areoles (circle of bumps with spines around it). Areoles are modified stem buds. They distinguish cacti from other spiny succulents. Station 11. Organ Pipe Cactus Organ pipe cacti are related to saguaros, and typical of the barrel or columnar species in the Cactaceae. Compare the areoles of this plant to other cacti. Station 12. Velvet Mesquite Identify adaptations of mesquite leaves to desert environments. In what type of microhabitats are mesquites found? Describe how mesquites play an important role in the desert community. What threatens mesquite today? Bio182 Botanical Garden 6

7 Station 13. Boojum Tree (Cirio = candle) What related species have you seen on this trail? Describe similarities and differences between these two plants. Station 14. Cardon (Elephant cactus) Cardons are related to saguaros. List three characters that biologists might use to distinguish between these plant species. Why are there no cardons in Arizona? Station 15. Baja Fairy Duster Inspect the leaves of this plant carefully and identify possible adaptations to their desert environment. Name a plant seen along this trail with similar adapatations:. Are they relatives? Station 16. Blue Palo Verde Identify leaf adaptations in this plant. What other plants have similar adaptations? Are these similarities homologous or due to convergent evolution? Describe how palo verde and cactus are an example of convergent evolution. Bio182 Botanical Garden 7

8 Station 17. Indian-Fig Prickly-Pear Cactus Prickly-pear and cholla cacti are more closely related to each other than either group is to the columnar forms (e.g. saguaro). How can you tell based on their scientific names? Look closely at the areoles of this plant. Can you see a difference between the areoles of opuntia vs. saguaro? (You will have more opportunities to compare areoles in the Cactus House.) Station 18. Woolly-Headed Barrel Cactus Why are these cacti called woolly-headed? What is adaptive about this trait? Are these cacti more closely related to prickly-pear or to saguaros? Station 19. Candellila (Wax Plant) What advantage is gained by covering the stem with heavy wax? What advantage is gained by dropping the leaves in the dry seasons? Station 20. Chain Fruit Cholla (Jumping Cholla) Describe a use for spines in this cactus not described elsewhere. Based on the areoles, identify a related cactus. Bio182 Botanical Garden 8

9 Part II. Succulent Gallery (Near Station 4 of Desert Discovery Trail) What is a succulent? Are Cacti succulents? Are all succulents Cacti? Succulence occurs in at least 50 families of plants. These succulent plants provide many examples of convergent evolution. What is convergent evolution? Which family appears most convergent to the cacti? (look for a euphorb). Describe these similarities. What evidence suggests that these plants are not related? Name two families of leaf succulents. Besides storing water in their leaves, what other similarity do these plants share? What is the advantage to this feature? Note the Madagascan Ocotillo (Alluandia procera) and compare it to the real ocotillo (Family Fouquieriaceae). Describe the similarities between these species. How would you explain the similarities between these species? Bio182 Botanical Garden 9

10 Part III. Cactus Gallery When did cacti evolve? What selective agent might be responsible for their evolution? Name a synapomorphy that defines Family Cactaceae: The spines of cacti are derived from the areole, a modified leaf s stipule (a projection of the petiole). The spines represent modified leaves. List four functions of spines (recall examples from the Desert Discovery Trail): Most cacti are succulents. Succulents store water in some part of their body tissues (root, stem or leaf). Based on what you have seen on the Desert Trail, where do most cacti store their water? How can you visually assess the relative amount of water stored in a cactus? Where else may cacti store their water? (provide an example) The genus Pereskia represents an ancestral branch of the cactus family (Subfamily Pereskioideae). It lacks many of the derived traits (desert adaptations) of most cacti. Identify an ancestral trait of this cactus relative to cacti of the Sonoran desert [What features are found in Pereskia that have been lost as adaptations to the desert? You might need to look at the ground.] Name the other two Subfamilies of the Cactaceae and one representative genus of each. Bio182 Botanical Garden 10

11 Part IV. Saguaro Hotel Saguaros are the dominant cactus in the Arizona portion of the Sonoran desert, and provide refuge to many other desert organisms. Return to the Desert Discovery Trail to find the display: Saguaro Hotel (next to station 10). Of the 11 species mentioned on this display, pick three and hypothesize the nature of their relationship with the saguaro: mutualistic / commensal / parasitic. [For additional help, view the film in lab after spring break.] Bio182 Botanical Garden 11

12 Part V. Checklist of Desert Adaptations for Water Gain and Conservation Use this page to make a summary sheet of desert adaptations. As you identify each adaptation, write it here with an explanation and example. Additional examples (i.e. convergent evolution or common ancestry) can be added as you go. Adaptation Example Bio182 Botanical Garden 12