A Story Map of Plant Ecology in the UCR Botanic Gardens

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Mojave yucca (Yucca schidigera) [below the path and next to the main road]. Yucca species are members of the Asparagus family (Asparagaceae) and are common in California shrublands and desert regions. They are characterized by long, sharp-tipped, rigid, evergreen leaves that are either clustered in stemless rosettes on the ground or on the tops of woody trunks. In Spring, they often bear large clusters of white flowers. The Joshua tree (Yucca brevifolia) is probably the best-known of all the yucca species, because it is the dominant species in the Joshua Tree woodland vegetation type of the Mojave Desert and is the namesake of the Joshua Tree National Park. The Mojave yucca also occurs in the Joshua Tree National Park.

Question 3      Sketch Y. schidigera with its cluster of leaves. What anatomical feature gives the leaves their toughness and rigidity? Clue: Note the leaf margins.

#3

Brittlebush (Encelia farinosa), located just before #3 of the Botanic Gardens Southwestern Deserts Tour, sign is a shrub that is commonly found throughout the Sonoran and Mojave Deserts. It is also a major component of the coastal sage scrub community, as was discussed above. It is drought deciduous, meaning that when water availability is low, it sheds it leaves to reduce water loss and relies on water stored in its stems until the next rainfall.

Question 4      Notice the color of the stems and leaves (if present). They are grayish-green. If you look closely you will see small hairs covering them. What purpose might these hairs serve?

#4

California fan palm (Washingtonia filifera) is located at stop #10 of the Southwestern Deserts Tour. The only native palm in California, W. filifera grows naturally in areas where there is a permanent source of water such as seeps, springs, or canyon bottoms. The presence of water and the shade provided by these trees provides a cool, inviting microhabitat, the oasis, in an otherwise arid environment. Washingtonia filifera often dominates these microhabitats and grows to heights of 15 meters with trunks up to one meter in diameter. The skirt of the fan palm is also important ecologically, providing protection from solar radiation and habitat for a variety of animals.

Question 5      Observe a leaf of the tree. Is it simple or compound? What obvious difference is there between these palm individuals and those that one sees planted in urban areas? Why might this be important in the natural oasis environment?

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Blue palo verde (Parkinsonia florida) is a common tree in the Sonoran Desert. Because it is a legume, you should see some bean-like seed pods hanging from the branches or on the ground beneath them. Parkinsonia. florida individuals are located just beyond (east of) the Washingtonia filifera. Another species, the Mexican palo verde (Parkinsonia aculeata) can be found in the Desert section along the trail between stops #15 and #16 of the Deserts of the Southwest tour, directly behind the concrete bench in the cactus garden. In southern California landscaping, the most common palo verde grown is a horticultural variety known as “Desert Museum”. This cultivar is a hybrid between blue palo verde, foothill palo verde (Parkinsonia microphylla), and Mexican palo verde. It was developed at the Sonoran Desert Museum in Tucson, Arizona.

Question 6      In what type of microclimate would you expect to find these trees? How are the stem and leaves adapted for a dry climate (see inset)? 

Question 7      The leaf of blue palo verde is very small (less than 2 cm long -- see inset). Is it simple or compound? What is the advantage of this morphology?

#6

We will now move to the Cactus Garden and see some representatives of the many genera of cacti from North and South America. With one exception, the Cactaceae is exclusively a New World plant family. It can be found throughout the Americas ranging from Minnesota to northern Argentina and even to the Amazon rainforests! 

The greatest diversity of cacti is found in the deserts, where they have developed a number of special adaptations to deal with their harsh environment. Some of these include CAM photosynthesis, thick waxy cuticles, fewer stomata, shallow root systems, and spines. The spines protect the succulent stems from herbivory, but when densely covering the stems, they can also be important in reducing heat buildup by reflecting light from their white or light colored surfaces. A dense and interlaced covering of spines or hairs can also serve to trap moist air near the surface of the plant and to reduce water loss.

You will now look at a few examples: (Use the arrow to view additional photos.)

Opuntia and Cylindropuntia (prickly pears and chollas) are two common and closely related genera of Cactaceae in California. Opuntia species (prickly pears) typically have no central stem, instead they have flattened stems called cladodes. Cylindropuntia species (chollas) have central cylindrical stems.

Question 8      Two interesting examples of these morphological types are Opuntia microdasys (photos A and B) and Cylindropuntia cholla (photos C and D). Make a drawing of each of these two types to show cladodes vs. jointed cylindrical stems.

Question 9      Reproduction in Opuntia and Cylindropuntia species. These plants can reproduce in two ways: sexually by producing flowers (photos B and D) or vegetatively through fragmentation. If a pad or cylindrical segment falls or is knocked off by a passing animal, it can root and form a new plant. Those species with sharp and hooked spines can attach to a passing animal and drop to the ground after being transported away from the parent plant. Why do you suppose the common name for O. prolifera is “jumping cholla”? Why would two types of reproductive strategies (sexual and asexual) be beneficial in a desert environment?

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Evolution of Cactus morphology. Cacti are best known for their stem succulence and spines, but ancestral forms have drought deciduous leaves and lack stem succulence. 

Question 10     Observe the two cacti in Photo A. On the left is a typical columnar cactus, the Peruvian apple cactus (Cereus repandus) and on the right is the rose cactus (Pereskia grandifolia). First examine the rose cactus in the photos. (Use the arrow to view an additional photo.)

The rose cactus has woody, non-succulent stems, unlike most cacti, but typical of most cacti, it has spines clustered in areoles. It also has leaves that are deciduous during the winter.

Give two characteristics that are ancestral for the family and have been lost in the more advanced columnar cactus and one characteristic that is ancestral and has been retained in most cacti.

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Century Plants (Agave spp.).  Called century plants because they flower so infrequently; in reality, plants normally flower after 8-30 years, depending on the species and the conditions under which it grows. For this reason, most of the plants you will see in the garden are in a vegetative condition. But there are enough specimens of different ages that there are usually some plants in flower every year or you can see skeletons of inflorescences from past years that have dried up and remain for many years after flowering. Agaves are rosette plants with thick succulent fibrous leaves with thick cuticles. The leaves are imbricate (overlapping) and curved to channel water down to the root zone. This growth form further shades the root zone and protects the roots from dehydration. Flowering inflorescences are either branched or unbranched and can grow to 30 feet tall.

Most Agave species typically reproduce both asexually and sexually. Asexual reproduction is especially important for Agaves as flowering is very episodic with plants flowering only once during their lives, after which they die (they are monocarpic). Although the rosette from which the inflorescence arises dies, plantlets that sucker from near the base of the plant and bulbils that form in the inflorescence continue to live on and can form new plants. As flowering is an infrequent event in these large species, asexual reproduction insures the perpetuation of the species. (Use the arrow to view an additional photo.)

 Question 11  Note the Agave attenuata (foxtail agave) (A) and Agave deserti (desert agave) (B) in the photo. Notice how they grow in clumps. Each individual rosette is a clone of the original plant and was formed asexually from a sucker. Sketch one of these plants. Notice how the leaves can be spiny or smooth. What do you think the leaves are storing?

Move back up the hill and over the crest until you see the boojum trees.

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Ocotillos (Fouquieria species). This genus of 11 species of spiny semi-succulent to succulent woody shrubs or trees is endemic to the southwestern US and Mexico. These xerophytic (arid or desert loving) species are extremely responsive to rainfall. For most of the year they are leafless, but in response to a rain shower they can sprout leaves within 72 hours. As the soil dries out, the leaves fall off. This cycle of leaf loss and regrowth can occur 3 or 4 times in one year. Fouquieria splendens (ocotillo) is the only Fouquieria species occurring in California. This tall spindly shrub with its bright red-orange flowers is conspicuous in the Sonoran Desert. Less familiar and more unusual is the boojum tree (Fouquieria columnaris). This columnar succulent has been characterized as an upside down carrot or parsnip and was called Cirio (candle) by the Spanish. The common name boojum was coined by a botanical explorer in 1922, because he thought it looked so strange that it reminded him of the mythical creature discussed in Lewis Caroll’s “The Hunting of the Snark”. (Use the arrow to view additional photos.)

Question 12     Four of the nine species in the Botanic Gardens that vary in branching and degree of succulence are shown in the photo. They range from a single thick succulent stem (e.g. A: F. columnaris) to two thick succulent stems (B: F. purpusii) to multiple and less succulent stems (C: F. macdougalii), to many non-succulent stems branched from the base (D: F. splendens). Notice the unusual shape of the main stem in F. columnaris (see above). Draw it. Why do you think it is so thick at the base compared to the other species (HINT: think cacti)?

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Proceed to the uppermost trail of the Cactus Garden and walk east towards the South African section. Along the way, see if you can find agaves, euphorbias, cacti, and puyas (spiny rosettes of the pineapple family from South America that look similar to agaves and yuccas). See if you can find examples of barrel cacti such as (A) Echinocactus grusonii, an endangered species in the wild (but common in cultivation) and (B) Ferocactus pilosus (Mexican lime cactus). Also note columnar cacti such as (C) Neobuxbaumia scoparia and (D) Pachycereus pringlei (cardon or elephant cactus), (E) Organ pipe cactus (Stenocereus thurberi), (F) Mexican organ pipe cactus (Stenocereus griseus), (G) the sprawling Echinopsis candicans (Argentine giant), and the very large pony tail palm (Beaucarnea recurvata). The saguaro is the largest cactus species in the continental US. It can weigh up to 8 tons (16,000 lbs.) and reach 60 feet in height! There is a saguaro specimen elsewhere in the Gardens, but it is relatively young, unbranched and only a few feet tall.

Q13     Sketch a barrel cactus: golden barrel (Echinocactus grusonii) or Mexican lime barrel (Ferocactus pilosus) and a columnar cactus: Neobuxbaumia scoparia or elephant cactus (Pachycereus pringlei).

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Continue walking east towards the southern African section and look at succulent euphorbias (e.g. large clumps of Euphorbia resinifera and Euphorbia coerulescens), the Madagascar ocotillo (Alluaudia procera), and aloes such as Aloidendron barberae and Aloe marlothii (Asphodelaceae). Some of these plants resemble cacti or other North American desert plants, because they have succulent leaves or stems and because they often have spines. This is an example of convergent evolution, the independent evolution of morphological and physiological similarities between unrelated species growing under similar environmental conditions, in geographically disparate environments. The plant that covers most of the south-facing slope in the South African section is rosea ice plant (Drosanthemum floribundum), a member of the ice plant family (Aizoaceae).

(Use the arrow to view additional photos.)

 Question 14     Look at the group of four photos (A-D). Which photos are of a Euphorbia and which are of a cactus? What are the characteristics that you can use to tell the two apart?

Observe the “Madagascar ocotillo” (Alluaudia procera) photos. Like the ocotillos we discussed above that occur in California and Mexico, this plant occupies similar arid environments in Madagascar. Like Fouquieria species, it also produces long thorny stems with small leaves that appear shortly after rainfall. However this plant occurs in a family, Didieriaceae, that occurs only in Madagascar. It is unrelated to the Fouquieriaceae. We would refer to North American ocotillos and the Madagascar ocotillo as another example of _____________ evolution.

Question 15     Find Aloe marlothii. How does this arborescent (tree-like) aloe (Photo A) resemble the Yucca schidigera (Photo B) that you sketched earlier?  Are the two species closely related (i.e. are they in the same family)?

Continue east along the trail to the slopes covered with rosea ice plant (Drosanthemum floribundum (Aizoaceae) on your left and various aloes on both your left and right. The name ice plant comes from the glistening of water vesicles in the leaves that look like tiny ice crystals (see inset) of this and related Aizoaceae species.

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III.      ADAPTATIONS FOR DEFENSE

In addition to adaptations to the physical environment, some plants have adaptations to protect them from the biological environment (i.e. animals). The next plant you encounter will illustrate one of these other adaptations.

Umbellularia californica (California bay laurel). This species is evergreen, so it should retain some leaves on it all year long. Pick a leaf, crush it in your hand, and smell it. The leaves are used as a seasoning in food. The odor is the result of secondary chemicals produced by the plant. (Use the arrow to view an additional photo.)

Question 16     Do you see any insect damage on the leaves? Why or why not?

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IV.      CONIFERS

As you walk through this section you will see several different conifers. Because many conifers tend to grow at higher elevations (above 4000 feet) they are frequently subjected to harsh environmental extremes such as intense heat and sunlight in the summer and dry, freezing temperatures in the winter. As a result, they often experience significant water stress. For this reason, the leaves are often reduced and needle- or scale-like, with thick cuticles and sunken stomata. They are also usually evergreen, living for several years before falling off. This allows the plant to photosynthesize and grow year round (albeit slowly). Another advantage to the evergreen habit is that there is no lag time while new leaves are being produced when water becomes available again. In contrast, deciduous plants lose leaves in response to cold or drought, so photosynthesis cannot occur until new leaves are formed each spring. In addition, evergreen trees often have thick protective bark, deep roots, and produce a large number of secondary chemicals in the sap for defense and wound protection.

Sequoia sempervirens (coast redwood) is the California State Tree and is one of the tallest tree species in the world.

(Use the arrow to view additional photos.)

Question 17     Why do you think the coast redwoods in the Botanic Gardens are not particularly tall?

Question 18     You will notice that a common feature possessed by most conifers is the presence of needle-like or scale-like leaves with very thick cuticles. What advantage do you think this adaptation might have for these species?

Question 19     When you walk through a coniferous forest, you will notice very few plants in the understory and a dense blanket of needles covering the ground. Why might this be? (HINT: Think about secondary chemicals in the needles). What other benefit might the needle blanket have for these trees?

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Sequoiadendron giganteum (giant sequoia). This tree species is native to California and is the largest living organism in the world. It is known to live for several thousand years and can grow to massive proportions. The largest known individual is named after General Sherman and is 272 feet tall with a trunk 35 feet in diameter and a circumference of 109 feet at the base. It has been estimated to contain over 60,000 board feet of timber, enough to build 120 average-sized houses. In fact, a single giant sequoia may contain more wood than is found on several acres of some of the finest virgin timberland in the Pacific Northwest. The trunk of General Sherman alone weighs nearly 1400 tons. By way of comparison, this is roughly equivalent to 15 adult blue whales, 10 diesel-electric train locomotives, or 25 average-sized military battle tanks. Of course the representative in the Botanic Gardens is much smaller and younger, since the Botanic Gardens is only about 40 years old.

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Metasequoia glyptostroboides (dawn redwood). This tree was thought to have been extinct for 20 million years, but was rediscovered in the 1940s in a remote region of China. It is related to both coast redwood and giant sequoia. One major difference between this species and the other two is that it is deciduous, losing its leaves in the late fall. If you can find some leaves, notice that they are a lot softer than the needles on the other conifers you are seeing today.

Question 20     Why do you think this species has softer, more mesic (moist) leaves than the other two redwoods species?

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Proceed up the hill and look for a very large foothill or gray pine (Pinus sabiniana). This pine is a native to California and is found in the foothills surrounding the Central Valley. Notice the long needles on the tree and the ground and how they are fascicled (in bundles). These fascicles are actually modified branches, but they do not elongate as typical branches would.

Question 21     Sketch one of these fascicles. What is the average number of needles per fascicle?

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Next to the pine is a deciduous tree that has large palmately lobed leaves and winged fruits. This is the big leaf maple (Acer macrophyllum). (A) It has the largest leaves of any maple species and is widespread in California in a variety of different plant communities. (B) The winged fruits of maples are called samaras. They are often caught in wind currents and carried some distance from the parent tree, where, if conditions are suitable, they will germinate. See if you can find one and toss it into the air.

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At the east end of the Rose Garden is a Calocedrus decurrens (incense cedar). Instead of needles, this conifer has scale-like leaves that completely enclose the branchlets (little branches). It is found at mid-elevations (average 6000 ft.) of mountains from Baja California to Oregon. It is economically important as it is used for making pencils, fencing, and furniture.

Question 22     Sketch a branch of incense cedar with leaves (see the photo to the right and enlarge if necessary).

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V.       MOIST ENVIRONMENTS

Take a quick detour through the Herb Garden to look at a few aquatic plants being grown in mini ponds. In general, aquatic plants have very thin cuticles and weak supporting tissue. Since the plant is growing in water, it does not need to develop rigid support tissues. Furthermore, aquatic plants are frequently subjected to water currents and need to be flexible to move with shifts in these currents. Because the plant does not need to develop a lot of supportive tissue, it can invest energy into producing large leaves.

There are six artificial mini ponds in the Gardens that contain aquatic plants including cattails, water hyacinths, duckweed, and water lilies. (Use the arrow to view additional photos.)

Question 23     (A): Water lilies (Nymphaea spp.) have large, flat, round leaves that float on the water surface. In some species (e.g. the giant Amazon water lily) these leaves grow so large that they can support the weight of a small child. Nymphaea species have tuberous roots that grow inthe mud at the bottom of ponds or other bodies of water. Sketch a leaf from the water lily.

(B): Cattails (Typha spp.) are large monocots in their own family, the Typhaceae, growing in one of the containers. Typha is able to grow in water to depths of up to about 3 feet. The cells in the leaves are very large with a lot of air space so that oxygen can get down to the roots that are growing in the mud. Typha also has underground stems (rhizomes) for extensive vegetative growth. Each year the leaves die back completely and the plant goes dormant until the following spring.

Question 24     Water hyacinth (Eichornia crassipes) is a free-floating, aquatic perennial native to the Amazon basin. One of the world’s fastest growing plants, a population can double in size in two weeks. For this reason, it has become a highly invasive plant in waterways outside of its normal range. In Florida it is illegal to possess this plant without a special permit. Note the swollen petioles. The petioles are like little floats that keep the plant on the surface of the water. Look at the section made through the petioles to observe the numerous air spaces or aerenchyma tissue (see inset). Sketch a cross section of the leaf petiole.

Question 25     Still bodies of water often have tiny free-floating aquatic plants growing on the surface. These are duckweed (Lemna). Duckweed, with its light green leaves, is one of the smallest of all flowering plants. Sketch a few leaves of the plants growing on the surface of this mini-pond.

Walk over and touch the bark of the cork oak (Quercus suber) growing behind the last concrete container. This evergreen species is native to the Mediterranean region of southwestern Europe and northwestern Africa. The bark of this species is used to produce corks for wine bottles. Cork oak is unique in its ability to regenerate its outer bark. After a tree reaches 25 years of age, it can be stripped of its cork once every 9 to 12 years without causing damage to the tree. A single cork oak, which lives up to 200 years, can be harvested over 16 times. Annual production of wine corks per year is slightly less than 13 billion.  

Question 26     Draw a leaf of the cork oak. Is it evergreen or deciduous?

Now follow the map and walk down to the turtle pond. Beginning at the pond and walking down the steps towards the canyon bottom, you will be introduced to two mesic environments. The first will be the pond and the second will be the canyon itself.

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You have looked at several communities in which water was the limiting factor for growth. Surprisingly, too much water can be problematic for plants, as well. For example, when soil is waterlogged or flooded, plant roots are unable to get enough oxygen for respiration and other basic functions. Many plants have overcome this problem through morphological adaptations such as hollow or inflated stems or roots that extend above the soil or water surface. A classic example of this adaptation are the protruding roots or ‘knee-like,’ pneumatophores, found in bald cypress (Taxodium distichum) trees in the Florida Everglades. A Mexican relative to the bald cypress, Taxodium mucronatum, grows next to the turtle pond in the Gardens. It grows in similar seasonally wet environments and also produces pneumatophores (see photo inset).

Question 27    (Use the arrow to view an additional photo.) Papyrus (Cyperus papyrus), growing in the turtle pond at the base of the fence (A), is a member of the Cyperaceae, the sedge family, and it is native to Africa. This is the plant that Ancient Egyptians used to make paper, as it once grew abundantly in the Nile delta. You will recognize it by its tall flowering stems (B). Members of this family are found in very wet areas all over the world from the tropics to the arctic. Notice the triangular shape of the stem and the presence of abundant aerenchyma tissue in the cortex (C). What other plant that we have seen in the garden has aerenchyma tissue?  The stems rather than leaves were used to make the paper. They were cut longitudinally in half, woven into a lattice and then flattened under heavy pressure (D).

Sketch the cross-sectional shape of the stem.

As you stand next to the pond, you are actually standing about midway up a canyon between two hills. Notice how cool it is as you walk down the canyon (the effect is more pronounced in summer). The temperature is due to a combination of cold air drainage from the hillsides (cool air sinks), high soil moisture, and shade of the tree canopy. When you enter a deciduous forest in spring or summer, you see tall trees with large, thin leaves and an abundant understory of shrubs, perennial herbs, and ferns. Many of the plants you see in the understory are very shade tolerant.

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In contrast to evergreen trees, such as most conifers, deciduous trees and shrubs lose their leaves on an annual basis, so essentially stop growing for that portion of the year. In regions with cold winters, such as the eastern and northern U.S. and high elevations in California, many species are winter-deciduous, losing leaves in winter, while at lower elevations in Mediterranean type arid or desert areas, many species are drought-deciduous, losing leaves in summer. In the spring as temperatures rise, winter-deciduous species produce a whole new set of leaves. Drought-deciduous species in California grow new leaves when the wet season begins in the autumn. The leaves of winter deciduous species are usually large and thin with thin cuticles, because water stress is not a problem.

Observe the leaves of the following trees.

Fraxinus pennsylvanica (red ash)

Populus fremontii (Fremont’s cottonwood)

Morus bombycis (mulberry)

Platanus racemosa (California sycamore)

Question 28     Based on that observation and the season, do you think each tree is deciduous (winter or drought) or evergreen? Sketch a leaf of each one that has leaves present (on the tree or the ground), making sure that you label your sketches correctly.

#22

Pinus coulteri (Coulter pine). This is another native pine of California, usually found at mid-elevations (around 4000-5000 feet) in the mountains from central to southern California. They grow throughout our local mountain ranges (the San Bernardino and San Jacinto Mountains). Coulter pines have the largest cones of all California pines, growing up to 15 inches and weighing up to 7 or 8 lbs. This great size has given this tree the nickname ‘widow-maker’ due to the danger posed by standing under the tree when a cone drops. It looks very similar to grey pine, but the needles are greener and the cones are larger.

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VI.      SHRUB COMMUNITIES (CHAPARRAL)

You have looked at two shrub communities today, chaparral and coastal sage scrub, both of which are found in southern California. Chaparral generally occurs at elevations of about 2000- 5000 feet in the mountains in southern California. It is characterized by evergreen, sclerophyllous (thick and leathery leafed) shrubs with a closed canopy and very little understory. We will look at a few members of this community here and then later (on your way out of the Gardens) you will see coastal sage scrub. Shrub communities similar to the ones found in southern California occur all around the world in places as diverse as Chile in South America, South Africa, Australia, and the Mediterranean regions of Europe and Africa. The common factor in these communities is the Mediterranean climate (described above). This is another example of convergent evolution.

Arctostaphylos densiflora (cultivar Howard McMinn) is a fairly large, evergreen shrub growing on the bank above the pathway. Manzanitas have smooth, reddish-brown stems and small to medium-sized, ovate, sclerophylls (Greek meaning hard-leaves) and are characteristic of chaparral vegetation 

Question 29     Sketch a manzanita leaf