Assignment Due in Lab: March 22 or 24 Name:

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1 Assignment Due in Lab: March 22 or 24 Name: Desert Botanical Garden 1201 N Galvin Parkway, Phoenix, Checkout a Desert Discovery Trail guidebook from your instructor to take with you. Go online (dbg.org) to check for normal business hours. You may work with a partner and turn in a single worksheet. Attach your DBG receipt(s) to earn credit! Cost: $8.00 with your Student ID (one guest allowed). Confirmation # Free entrance on February 9 and March 8 (second Tuesdays of each month). Introduction Desert biomes are defined by their low precipitation, less than 30 cm (12 in) per year. Although temperatures vary between deserts, 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 (10 in) of rain per year. This precipitation is concentrated in two separate seasons: winter storms and the summer monsoon. Summer temperatures may exceed 48 0 C (118 0 F) with occasional overnight freezes in the winter. Many animals that live in the desert either migrate or aestivate (e.g. hibernate) at times of stress. Most plants, however, cannot migrate. [How can plants migrate or aestivate 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 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. Summarize the variety of desert adaptations seen today on the last page of this worksheet. 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 typical cactus structures. As you observe diverse cacti, note their variation of structures. Which parts are leaves? stems? roots? What new adaptations evolved in these organs? The DBG displays other Sonoran plants as well as plants from deserts around the world, some of these plants share similar adaptations. Unrelated organisms with similar adaptations are examples of convergent evolution. The Succulent Gallery and Agave Yucca Forest displays provide diverse examples of convergent evolution and alternative life history strategies to life in the desert. Note: there are many other plants and animals on display in the garden. Take extra time (family? friends? picnic?) and enjoy! Bio182 Botanical Garden 1

2 Desert Ecology Lab: Transects March 22 & 24 Throughout your tour of the DBG, look for plants we will count at Thunderbird Park. You will need to identify these plants on our field trip, March 22 & 24. 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. Cactus Family [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 (DDT) The Desert Discovery Trail (DDT) begins near the entrance of the garden and makes a long loop. Several years ago, the DDT included a series of numbered stations to highlight plants that were described in the companion Desert Discovery Trail guidebook. The guidebook is out of print and some of the species along the trail have changed, but they have been replaced by congeners and the guidebook still provide many answers to the questions on this handout. Be sure to checkout a copy from your instructor before you go. Please Do Not Write in the Guidebook. The following directions should help you find examples of the desert plants needed to complete this assignment. In addition, pick up a current map of the garden trails at the visitor center. One plant, the Jojoba (Book #5) is found several places along the trail. Answer questions about the jojoba on page 8 of this handout. Directions: Begin at the start of the DDT and go left (clockwise). Continue around the loop until you return to the start point. Along the way you will find the Cactus & Succulent Galleries and the Berlin Agave Yucca Forest. Questions about these exhibits are in pages near the end of this handout. If you have trouble finding a plant, ask one of the volunteer gardeners. 1. On the left side of the trail near the start are two displays: What is a Cactus and Are you Saguaro Smart? Read these displays and try to answer the questions. You will write about Saguaro and other cacti later on this worksheet. 2. Organ Pipe Cactus (Book #11): On the Right, just past the Cactus Displays This cactus, like most members of the Family Cactaceae, lacks photosynthetic leaves. Note the areoles on the stem (circle of bumps with spines around it). Areoles are modified stem buds. They distinguish cacti from other spiny succulents. What cladistic term applies to aeroles, as a defining feature of the Cactaceae? Cactus spines are modified leaf parts that arise from areoles. Most cacti use their stems for photosynthesis instead of leaves. 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? Bio182 Botanical Garden 3

4 3. Creosote Bush (Book #2): Right side of trail, on both sides of the Organ Pipe This is one of the most abundant plants in the Sonoran Desert. Write its scientific name (binomial) and Family. Describe two structural features of this plant that may be adaptations for the desert. What are two functions of the creosote bush resins? 4. Century Plant (Book #6): On right, about 10 m past Creosote bush. See also the nearby display of Century Plants and Aloe Display Name the family that includes agaves: What is the geographic distribution of this family? Besides storing water in their leaves, what other aspects of their leaves might be adaptive for life in the desert? What is the advantage of having all its leaves in a tight cluster? 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? 5. Old Man of the Andes (Book #18. Woolly-Headed Barrel Cactus) - on both sides of trail, about 22 m past the Century Plant (note: Old Man of the Andes is an extreme type of woolly cactus, much woollier than the book example) Various species of cacti have long hairs or woolly-heads. What benefits are derived from this adaptation? Bio182 Botanical Garden 4

5 6. Aloe Collection (Book #7) and nearby Century Plant & Aloe Display; Right side, about 50 m past the Old Man of the Andes Name the family of this species: Which plant family seen so far most resembles the aloe? Describe these similarities. Aloes are iteroparous. Based on this information, and the geographical information available, do you think the similarities between aloes and agaves are due to common ancestry or convergent evolution? Explain. 7. Boojum Tree (Book #13): Left side, just before Century Plant Collection What is the scientific name and family of this species? Describe adaptations to the desert environment. Continue along the DDT you will pass the entrance to the Berlin Agave Yucca Forest (left). You can explore this exhibit now (see page 11 of worksheet) or continue on the DDT and return later. Continue on the DDT and cross the bridge. 8. Mesquite (Book #12): Right side, just across bridge 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? 9. Ocotillo (Book #8): Right side, about 20 m past Mesquite, set back from trail What is the scientific name and family of this species? Describe the meaning of drought deciduous. How is this an adaptation? What related species have you seen on the trail? Bio182 Botanical Garden 5

6 Continue along the DDT to the entrance of the Plants and People of the Sonoran Desert Loop Trail (PPSD). Just before the PPSD trail, look for Prickly-Pear, Right side of DDT, and on the Left side of DDT is a large Beaked Yucca. 10. Prickly-Pear Cactus (Book #17) right side of trail What is the scientific name (binomial) of this species? Look closely at the areoles of this plant. Can you see a difference between the areoles of prickly-pear vs. organ pipe cactus? (You will have more opportunities to compare areoles in the Cactus House.) 11. Beaked Yucca (Banana Yucca, Book #9) left side of trail What is the scientific name and family of this species? What related plant(s) have you seen on the trail? 12. Continue on trail to Saguaro Hotel (Book #10) left side, about 35 m What is the scientific name of this species? Why do saguaros have pleated stems? Compared to other cacti in the US, the saguaro is the. Saguaros are the dominant cactus in the Arizona portion of the Sonoran desert, and provide refuge to many other desert organisms. The Saguaro Hotel display names 11 species that interact with saguaros. Pick three and hypothesize the nature of their relationship with the saguaro: mutualistic, commensalistic or parasitic. What is gained or lost by each organism in these interactions? 1. Organism (name) Organism gain/loss? Saguaro gain/loss? Symbiosis Bio182 Botanical Garden 6

7 13. Various species of Cholla (Chain Fruit or Jumping Cholla, Book #20) a few m past Saguaro on Right Note the similarities of cholla areoles to those of prickly-pear. Based on the similarity of their areoles and other traits, scientists hypothesize that prickly-pear and cholla cacti are more closely related to each other than either group is to the columnar forms (e.g. saguaro and organ pipe). How is this hypothesis expressed in their scientific names? Describe a use for spines in this cactus not described elsewhere. 14. Blue Palo Verde (Book #16) amongst the Cholla on right, across from the path to the Patio Café Write the scientific name (binomial) and family of this species: Identify leaf adaptations in this plant. What part of the tree photosynthesizes when they shed leaves in the dry season? What other plant uses the stem for photosynthesis? Is this similarity homologous or due to convergent evolution? Explain. 15. Baja Fairy Duster (Book #15) at Southwest corner of trail on right (new feature here on left) Inspect the leaves of this plant carefully and identify possible adaptations to their desert environment. Name a plant seen along this trail with similar adaptations:. Are they relatives? Explain Bio182 Botanical Garden 7

8 16. Jojoba (Book #5) there are several plants along the trail, but not well marked. Ask for help. List three adaptations of the jojoba leaf to the desert environment. 17/18. Senita & Totem Pole Cactus (Book #3 & #4) After completing the Desert Discovery Trail, return to the entrance of the Cactus and Succulent Galleries. You will find large examples of these cacti on your left as you leave the DDT. What is the scientific name of Senita cactus? What is unusual about the spines on this species? Describe two ways in which these spines help the plant survive in the desert. What is the scientific name of the Totem Pole Cactus? Why does the Totem Pole Cactus have a different common name than the Senita? Apply the Morphological Species Concept to these two plants (Senita & Totem Pole cacti). Should they be considered one species or two species? Explain. Will these two types interbreed? Apply the Biological Species Concept to this problem. One species or two species? Bio182 Botanical Garden 8

9 Part II. Succulent Gallery entrance near Audio Station 19 What is a succulent? Are Cacti succulents? Are all succulents Cacti? Succulence occurs in about 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 our local 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 Where 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 leaf parts. 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, i.e. 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 two other (larger) Subfamilies of the Cactaceae and a genus of each. Bio182 Botanical Garden 10

11 Part IV. Agave Yucca Forest Scientists include both agaves and yuccas in Family Agavaceae based on their similar morphologies. List two of their common features that adapt these plants to life in the desert What new evidence supports the monophyly of this group? Agaves are generally monocarpic, whereas yuccas are polycarpic. Define these terms and suggest a possible advantage for each strategy. Monocarpic: Polycarpic: The Yucca Moth has a symbiotic relationship with Yucca plants. Is it parasitic, mutualistic, or commensalistic? Explain. 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 (at least five for full credit). As you identify each adaptation, describe it with an explanation of its performance benefit, and cite an example (genus name appropriate). Additional examples (i.e. convergent evolution or common ancestry) can be added as you go. Adaptation Example Bio182 Botanical Garden 12