Torrey Pines Docent Society 2019

Cactus Adaptation and ConservationCacti are in the Lodge garden, the Whitaker Garden, and almost all the trails in TPSNR, but there is a lot more to simply look for the silver Argiope spider and the cochineal. Cacti exhibit many specialized adaptive features to an arid climate. For children, the discussion can revolve around adaptation. For adults, one can highlight conservation issues that confront slow-growing cacti.

Key points:

• Green stem with spines? This is the first visual clue that cacti are specialized for something. What we observe are adaptations to survive in a dry climate. To reduce evaporative water loss (transpiration loss), cacti have several adaptations:

◦ Cacti make spines, which are modified leaves, to reduce surface area and to protect themselves from thirsty animals. (Nonetheless, there may be tiny foliage leaves on a very young stem.)

◦ The stem takes over the task of photosynthesis. Not only that, the stomata (microscopic openings for gas exchange) on the stem are closed during the day, and are only opened at night.

◦ Without sunlight, the plant cannot make use of carbon dioxide immediately, and so it stores the gas as malic acid, which is the taste of sour apples. During the day, the plant converts malic acid back to carbon dioxide for photosynthesis.

◦ To reduce surface area, the entire plant is made of stems or stem segments. At the extreme, Barrel cactus takes on a globe-like shape.

◦ Cacti may have ribs or tubercles which allow the stem to expand or contract depending on their water content.

◦ The stem has a heavy waxy surface (cuticle).

• Some specialized spines on the barrel cactus make a sugar solution to attract ants.The ants in turn drive away insect herbivores in a food-for-protection mutualism.

• For protection, prickly-pear-related cacti also make glochids, essentially tiny, hair-like spines. They appear at the base of spines and on the fruits, which become the prickly-pears.

• The adaptations to survive in a dry climate come at a cost and that is cacti grow very slowly. As a result, many cacti and some succulent species are threatened because of loss of habitat and illegal poaching for gardening and home décor.

What is interesting about cacti?

Most people know what a cactus is. They are the ones with succulent green stems and fierce spines. We may consider cacti as iconic of the American Southwest deserts, but the cactus family, Cactaceae, is quite diverse throughout the Americas. There are about 127 genera and close to 2,000 species in the family. The plants also have a large variation in shape and size. Members of the family can be found in hot deserts, cold deserts, dry grasslands, coastal sage scrub, chaparral, and even alpine zones above the treeline. Regardless, these are all semi-arid or arid habitats.

Where are the leaves? What are the roles of the spines? Why doesn’t the Indian fig have spines? Why are the stems green? Is this how I can survive in the desert? In short, cacti are extremely well adapted to dry environments—they are xerophytes. As aforementioned, cacti live in arid or semi-arid habitats, and as such they are highly specialized to survive in such environments. They carry out photosynthesis in their stems,and the spines can be considered as modified leaves to protect them from thirsty animals. The long answer follows. We shall look into their unique adaptations or specializations.

The descriptions will focus on the key species in TPSNR. They are the Coast prickly-pear (Opuntia littoralis), Coastal cholla (Cylindropuntia prolifera), the rare Coast barrel cactus (Ferocactus viridescens), and the introduced Indian fig (Opuntia ficus-indica). A few illustrations also make use of species from Anza-Borrego.

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Figure 1. Left: Coast barrel cactus (Ferocactus viridescens) with prominent ribs; Right: A close up on the two different types of spines. (The smaller, finer white ones mighthave secretory glands at the base, but no confirmation of this yet.)

Cactus morphological features

The cactus stem has many specialized features. For one, the stem has taken over the task of photosynthesis and this will be revisited below. Here, we look into the structural characteristics, and see how the stem is specialized for water conservation.

Stem structure and shape: Without leaves, cacti are easily recognizable by their stems. The stems generally can be cylindrical or flattened. Formally, a modified stem that replaces the functional role of leaves is a cladode.1

Columnar cacti are the ones with a main cylindricalcladode that we commonly call chollas. One example is theCoastal cholla (Cylindropuntia prolifera). We referflattened cladodes as pads. Two examples are the Coastprickly-pear (Opuntia littoralis), and Indian fig (Opuntiaficus-indica).

All cacti take on some compact shape that may reducethe surface area. Here, the Coast barrel cactus (Ferocactusviridescens) is probably the most specialized. Its globular(globe-like) shape has a very small surface area to volumeratio, and is ideal for water storage.2

Many cacti have ribs and tubercles, which are smallnodule-like projections. Ribs are most distinct with a barrelcactus (Fig. 1). These structures allow the cactus stem toexpand or contract depending on water content. The ribs in

1 Another term that one may come across is phylloclade, a modified branch. For cactus, cladodeis the proper term. There is another similar spelling term, phyllode, which is a modified petiole that resembles and functions as a leaf. This is what we find in acacia (genus Acacia in Fabaceae) plants.

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Figure 3. The woody skeleton inside Buckhorn cholla (Cylindropuntia acanthocarpa) in Anza-Borrego.

Figure 2. Coastal cholla (Cylindropuntia prolifera). Left: A young stem made of tubercles; Right: A grown, expanded stem with tubercle-like undulations.

particular make a folded surface that impart strength to the structure. The groves on a ribbed surface also help to channel rainfall to the roots.

When the sun is at an angle, the ribs provide a partial shade. Some cacti, notably the barrel cacti (genus Ferocactus) are known to tilt slightly toward the sun, especially on a slope, such that only the smaller top faces direct sun.

Cacti with flattened stems have neither distinctive ribs nor tubercles. A columnar cactussuch as the Coastal cholla can have tubercle-like undulations (Fig. 2). The Coastal cholla is unusual; its young cladode is made of tubercles. As the stem grows, the tubercles swell and the bases stretch out to become tepee-like. This is also the growth pattern with pincushion cacti (genus Mammillaria).

Unlike coconuts, we will not find liquid water. Cacti use water storage tissues, specialized thin-walled cells with a large water vacuole. The stem of a well hydrated Indian fig is close to 90% water. Some cacti can convert water into a mucilaginous substance that does not evaporate readily and lowers the freezing point of the tissue such that the cacti can survive cold winters.

To seal in moisture, cacti have thick, waxy cuticle on the surface. To reduce transpiration loss, cacti practically have no leaves (more on this with the spines below), and the stem takes over the photosynthesis function.

Even though a cactus is mostly water, it is considered a woody plant. All cacti make a vascular cambium that produces both secondary (woody) xylem and secondary phloem.3 However, the xylem does not become heartwood—the plant uses the space for water storage tissue. The secondary xylem forms instead a hard fibrous matrix. This is most

2 Given a solid object, the sphere has the smallest surface area to volume ratio.3 New, primary growth makes xylem that does not contain lignin, the substance of woody

tissue. Subsequent growth of a stem laterally makes xylem that is lignified, and is referred to as secondary xylem, or as sapwood.

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Figure 4. Two views of glochids and spines arising from areoles in Coast prickly-pear (Opuntia littoralis).

evident with a dead and partly decomposed cholla that exposes a cylindrical chain link fence-like woody skeleton (Fig. 3).

Areoles, spines and glochids: With cacti, we do not find recognizable branches. Instead, the plants bear areoles, structures unique to the Cactaceae family. An areole is a much reduced shoot (axillary bud4) that appears as either a little pad or even a slight depression or pit under dry conditions, but from which grows the spines, glochids, flowers, stems (cladodes), and stem arms on the saguaro in the Sonoran Desert.5 In short, the small oval thing at the base of the spines of a cactus is an areole (Fig. 4).

Among things that grow from an areole, spines are the most evident, and they generallyappear in clusters. We can say that spines are modified leaves.6 To be more precise, cactusspines are modified scales grown from an axillary bud (areole). As a young spine grows from a bud, it quickly turns into a dead lignified fiber.7 Sometimes, the spines are coveredby a loose sheath formed from the dried epidermis. This is presumably common with the Cylindropuntia species, but this is not evident in the Coastal cholla. (But in Anza-Borrego, we can observe that with the Buckhorn cholla, Cylindropuntia acanthocarpa.)

4 Areole is from the French aréole, which is taken from the Latin, areola, the diminutive of area, referring to a small open space or garden. In green plants, an axillary bud is an embryonic shoot located on the upper edge at the base of a petiole. The axillary bud is one type of growing shoot, and in cacti, this bud becomes the areole. The areoles contain shoot apical meristem (see next footnote).

5 The areole has what is called the shoot apical meristem (SAM). Meristem is undeveloped plant tissue that can grow into other kinds of cells and structures. They are equivalent to stem cells in animals. Meristem can be found in the root and the tip of a growing shoot (stem tip), in which case it is called the SAM.

6 Thorns are modified stems.7 Lignified is a scientific way of saying woody. Lignification is the process by which a plant

deposits lignin in the cell walls to make a rigid, woody structure. However, a cactus spine maynot appear as woody to the general public, and so using the term lignified may cause less confusion.

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Figure 5. Two cacti with dense spine clusters. Left: Velvet cactus (Bergerocactus emoryi) planted near the Lodge garden; Right: Teddy-bear cholla (Cylindropuntia bigelovii) at Anza-Borrego.

The nature of the spines varies. Barrel cacti are notable for their fierce looking stout spines, and hence their genus name Ferocactus. In some cacti, the spines are so dense that they help to condense morning dew and to provide a bit of shading for the stem (Fig. 5).

Spines are evolved primarily to protect the plant from animals. They are not effective against small insect herbivores like the leaf-footed bugs (family Coreidae among the true bugs Hemiptera). Several cactus genera make special spines that bear secretory glands at the base. These glands make a sweet nectar-like secretion, called extrafloral nectar, that attracts ants. These ants drive away herbivory insects. Thus the two partners form an ant-cactus mutualism, or a food-for-protection mutualism. Locally, the Coast barrel cactus (Fig. 1) is known to bear specialized extrafloral nectar secreting spines, and they attract as many as 18 native ant species, visiting one kind at a time.8

8 The presence of the invasive Argentine ant can alter the mutualism. See articles listed in the bibliography.

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Figure 6. Clusters of glochids on a cladode of Beavertail cactus (Opuntia basilaris) at Anza-Borrego, and a closeup in the insert. Without a magnifying glass, glochids appear as an innocent looking bump.

Figure 7. Foliage leaves on a young cladode of Coast prickly-pear (Opuntia littoralis). The image on the right is a slightly older cladode showing how the spines are starting to develop just above the leaves from the areole.

Glochids are modified spines developed as tiny, thinner-than-hair bristles, and are unique to the subfamily Opuntioideae (only opuntioids have glochids).9 They are nastier than spines in the irritation that they cause. Even a gentle touch will dislodge them, and they break at their base as a cluster together. They are so short that they are embedded entirely in our skin epidermis and are extremely difficult to remove. We can find glochidsat the base of spines growing from the same areole, say, on Coastal chollas (Fig. 4). The fruit of the Opuntia has no spines but only glochids. Indeed, this is how the name prickly-pear came about—the pear, which is the fruit, is prickly with glochids. The Beavertail cactus (Opuntia basilaris) out in Anza Borrego is so specialized that it has no spines but protected entirely by these irritating glochids (Fig. 6).

Cacti do make foliage leaves, but they are small, conical-shaped, and present only on very young stems (Fig. 7). As soon as the stem expands, the tiny leaves fall off, while its axillary bud develops spines and glochids. Why do they do this? A possibility is that the leaves help to speed up the growth of a young cladode. As soon as a stem grows large enough such that the contribution from the tiny leaves is insignificant, they are shed to reduce transpiration loss.

Roots: Cacti generally have shallow but extensive root systems to capture moisture from light rains. Some cacti also make the so-called rain roots. They are tiny roots made to take up water after a good rain, but die off quickly when dry weather returns.

CAM Photosynthesis in Cactus

A result of functional adaptation to survive in arid and water-stressed environments, photosynthesis in cacti is different from what we learn in introductory textbooks. Before we address that, we should review the basic principles. In very simple terms, photosynthesis is a biochemical process by which carbon dioxide (CO2) and water are converted to oxygen and glucose, a six-carbon sugar, utilizing energy in sunlight. The process involves a series of very complicated steps. In green plants, these steps take placein a cell organelle called chloroplast, which contains chlorophyll. We know chlorophyll as the green pigment crucial to absorbing light energy and transferring it to drive subsequent steps in photosynthesis. What makes things complicated is that there are different types of chlorophyll, and different green plants can carry out the photosynthetic steps in different pathways.10

Clearly, cacti are different. Without leaves, the cactus stem is the main photosynthetic organ, and its skin bears stomata, the microscopic openings for gas exchange that normally are present in the leaves of green plants. To reduce water loss (transpiration loss), the density of stomata on cactus stems tends to be lower than a typical leaf. More important, in reverse temporal order of a typical green plant, the cactus stomata are

9 Opuntioideae, the opuntioids, contains 15 genera, including the prickly-pears Opuntia, and thechollas Cylindropuntia. Note that the Velvet cactus, genus Bergerocactus, is in the Cactoideae subfamily.

10 Details can be found in biochemistry textbooks.

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closed during the day, and they open only at night.

Hence in darkness the stomata of cacti open up and allow carbon dioxide to diffuse intothe stem. However without sunlight, the plant cannot utilize carbon dioxide immediately. So the plant converts CO2 into malic acid for storage during the night. Next day with the sun out, the malic acid is converted back to CO2 for photosynthesis. All these activities occur inside the cells that contain chloroplasts.

This strategy to store carbon dioxide as malic acid at night is not uncommon in the leaves of succulent or xerophytic plants. In fact, this form of photosynthesis is named Crassulacean acid metabolism (CAM), after the stonecrop family, Crassulaceae. The species in the agave family, thus including the yucca plants, work this way too.

Malic acid is what imparts the sourand tart taste in many fruits, especiallyunripe ones. Malic acid was firstidentified in apple, genus Malus. Thinksour green apples. So there can be aslight taste difference depending onwhat time of the day one harvests acactus pad for consumption.

Cacti grow only slowly

All the aforementioned adaptations tosurvive in a dry climate come at a cost.There has to be a trade off and that is aslow or very slow growth rate. (It maynot appear so with the Indian fig. SeeBibliography.) Without foliage leaves,the photosynthetic surface is restrictedto the stem and thus is very small. Thislimits the primary productivity of theplant. While the strategy of closing upthe stomata during the day and makinguse of CAM photosynthesis is great inreducing transpiration loss, there isenergy cost in capturing carbon dioxidefirst as malic acid. Here, the overallphotosynthesis efficiency iscompromised. As a result, cacti growonly slowly.

There are few studies on the growthrate of cacti, perhaps because themeasurements would take a lot longer

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Figure 8. Three examples of showy cactus flowers. From top: Coast prickly-pear (Opuntia littoralis) with a bee, California barrel cactus (Ferocactus cylindraceus) with more notable separate stigmas, and Beavertail cactus (Opuntia basilaris).

than a typical research grant. A commonly cited example is the saguaro (Carnegiea gigantea) from the National Park Service. A saguaro grows between 1 and 1.5 inches per year during its first eight years. During its first year, the growth is even slower; a baby saguaro is about 3 mm (a bit above 1/10 inch) tall by its first birthday. The saguaros that bear stem arms are at least 50 to 70 years old.

Conservation challenges of cacti and succulents

The slow cactus growth has also led to the demise of many cacti worldwide. In addition to habitat loss due to development and agriculture, some cacti and other succulent plants are threatened by people poaching them for gardening and home decor. The Coast barrel cactus, which grows extremely slowly, is one such victim. This cactus is not on the federal or California state endangered list but the California Native Plant Society (CNPS)considers the plant to be seriously threatened in the state (code 2B.1).

Elsewhere, the poaching of the saguaro in the Saguaro National Park has gotten so severe that park rangers have been inserting identification microchips into the stem to deter criminal activities.

With succulent plants, the Liveforever (or Dudleya) plants in the stonecrop family are prime targets for poachers to supply the hot Asian markets. In the last couple of years, theCalifornia State Fish and Wildlife officials have caught and indicted a good handful of poachers shipping thousands of plants to Korea and China.

In TPSNR, the Short-leaved Dudleya (Dudleyabrevifolia) is listed as a California stateendangered species. This plant is not a target ofpoachers because it is tiny. However, by the sametoken, the plant can be trampled under foot easilyby the unknowing public. Thus certain areas inthe main Reserve and in the Extension have beenfenced off to protect them.

Cactus flowers and reproduction

Cactus flowers are notable for being big andshowy—key features to compete for pollinators(Fig. 8). They attract and are pollinated by a hostof pollinators. In addition to bees, they welcomehawk-moths, hummingbirds, and bats. Theflowers are bisexual with pistil and stamens.Beyond this, cactus flowers have several uniquefeatures.

The flowers have many sepals and petals. Thesepals are colored and shaped like the petals, so

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Figure 9. Flower stages on an Indian fig (Opuntia ficus-indica). At the bottom is a developing pericarpel, at the top a developing flower bud, and in the middle a flower starting to bloom. Note how the pericarpel is covered by glochids.

much so that perianth (collection of sepals and petals) is the term used to describe cactus flowers. The flowers have numerous stamens, almost lawn-like surrounding a stocky style. Atop the style is a stigma that is multi-lobed, indicative of a large number of fused carpels. The cactus fruit is a many-seeded berry. The stigma usually matures later than the anther, making it difficult for self-pollination. The flowers of some cacti like the saguaro (Carnegiea gigantea) are self-incompatible.

In some species, the motion of an insect pollinator within the flower causes stamens to bend inward to dust the insect with pollens. Some sources consider the stamens to be thigmotactic. But it is hard to tell the difference when we see a bee scurry energetically through a stamen mat.

The ovary of cactus flowers is inferior, meaning that it is located below the perianth and the stamens (Fig. 9). The bases of the stamens and the perianth are fused together. The pericarpel (containing the ovary and thus the fruit) appears as if it is a new growth from a stem (cladode).

The colors of the stigma, anther and the perianth are usually in strong contrast, probably a visual cue for pollinators. For flowers with a vibrant red perianth, the color can be due to pigments called betalains instead of the more common anthocyanins. Betalains are responsible for the deep red color of beets (genus Beta) and bougainvillea flowers.

Cacti are also very capable of asexual reproduction. Vegetative propagation is most notable with the opuntioids (locally Opuntia and Cylindropuntia). They can easily make aclone of themselves from a detached stem segment. Because the covering of the fruit is essentially stem tissue, some opuntioids can regrow from the fruits, but there is no report of this happening with the local chollas and prickly-pears.

Opuntias

With about 200 species, Opuntia is the largest genus in Cactaceae. Their main characteristics is flattened cladodes that are joined edge to edge. Most of them have spines, but all of them have glochids. The glochids may not be noticeable on the Coast prickly-pear (Opuntia littoralis), but they are at the base of the spines and on the fruits.

Because of the adaptability of opuntias, many of their species have been introduced outside of the Americas. The most notable is the Indian fig (Opuntia ficus-indica). This isa domesticated (or cultivated) crop—why it has no spines and the pads are thicker. It was cultivated for so long and widely that its exact origin is no longer known, but it is very probable that the plant resulted from the work of the Aztecs in Central Mexico.11 There are over a hundred species of opuntias endemic to Mexico, and Opuntia species hybridizeeasily. The name of the pad, nopal, is taken from a Nahuatl word for pads, and nopales

11 Side tidbit: Archaeological studies and genetic analyses have found that corn (maize, Spanish maíz, scientific Zea mays) was domesticated from the wild, ancestral teosinte as early as 8,700years ago by the Mesoamericans.

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are used in a good number of Mexican dishes.

Spanish conquistadors introduced the Indian fig to Europe near the beginning of the 16th century. The plant was introduced so long ago and naturalized so well throughout southern Mediterranean regions that the etymology of Opuntia is ascribed to Opus, an Ancient Greek city during the days of Pliny and Theophrastus.12 Regardless, the species name ficus-indica literally means fig from India. To the early European explorers, they thought they had discovered the East Indies, and the fruit of this plant sort of reminded them of the fig. (The shapes of the fruits are not the same. Fig is native to the Middle East, but it was transplanted to Europe so long ago that it was even in the Roman diet.)

Today, the Indian fig is farmed commercially in more than 20 countries, primarily for the fruit, which is also called the tuna. Why? For a ripe fruit, the pulp inside is so red that it reminds people of a bluefin tuna.

The Kumeyaay did not farm the Indian fig. They harvested the fruits from the variety of prickly-pear species that grew in the region. They also devised many clever ways to get rid of the glochids, including making a tong out of Mojave yucca leaves to pick the fruit. They also ate the nopal, but it was not a major food staple.

Another notable Opuntia is the Erect prickly-pear (Opuntia stricta) native to tropical coastal areas of the Americas and the Caribbean. The British imported the plant to Australia in the 19th century in their attempt to establish their own cochineal scale insect (genus Dactylopius) red dye industry. Nonetheless, they picked the wrong Opuntia and the species of Dactylopius. Even though the experiment failed, the prickly-pear invaded some 15,000 square miles of farmland. The Australian government finally put the prickly-pear under control by importing the Cactus moth from South America in the early20th century.

On the note of the wrong species of Dactylopius, the Aztecs used a domesticated variety of cochineal. (They called cochineal nocheztli, blood of the nopal.) The cactus that this insect grew on? Primarily the Indian fig.

Annotated Bibliography

● General information related to cactus

Greenfield, Amy Butler (2006). A Perfect Red: Empire, Espionage and the Quest for the Colour ofDesire (Random House).

12 The naming of Opuntia might be a misunderstanding of time and that the plant was not native.Pliny the Elder wrote about some edible plant near Opus. Theophrastus wrote about some spiny plants. But both of them lived well over a thousand years before Columbus. Many people considered Pliny indeed saw a cactus-like plant because it was written by Umberto Quattrocchi in his authoritative World Dictionary of Plant Names.

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– An excellent historical account of the history of cochineal, including the domesticated insect andcactus.

Mauseth, James D. (2006). Structure–Function Relationships in Highly Modified Shoots of Cactaceae. Annals of Botany 98, 901–926.– A very detailed, invited review. Excellent images.

Morhardt, S. & Morhardt, E. (2004). California Desert Flowers: An Introduction to Families, Genera, and Species (University of California Press).– Has a short chapter on Cactaceae.

Rebman, Jon P. & Pinkava, Donald J. (2001). Opuntia Cacti of North America—An Overview, Florida Entomologist 84, 474-493.– A review covering the morphology, adaptation, and reproduction of the opuntias.

Wilken-Robertson, Michael (2017). Kumeyaay Ethnobotany: Shared Heritage of the Californias, pp. 159-161 (Sunbelt Publications).– On the ingenious ways that the Kumeyaay harvested and processed prickly-pear fruits. Wilken wrote that the Kumeyaay did not use the nopal as a major food source, but they did eat them. It was mentioned in Delfina Cuero’s autobiography.

● Related to growth rates

Bowers, Janice E. (1996). Growth Rate and Life Span of a Prickly Pear Cactus, Opuntia engelmannii, in the Northern Sonoran Desert. The Southwestern Naturalist 41, 315-318.– Bowers measured the growth rate by the number of cladodes. For Engelmann's prickly-pear, a ten-year-old plant has as few as 3 cladodes (up to about 6), but by 20-year-old, it has a bit over 100 cladodes (growth is not linear). On average, 20% of the cladodes initiated each year can be lost to abortion or predation (maybe why the young plants grow so slowly). The smallest plants capable of flowering has 6 to 13 cladodes, representing a range in ages from about 9 to 11 years—so a young plant allocates its resources to vegetative growth.

de Cortazar, V. G. & Nobel, P. S. (1992). Biomass and Fruit Production for the Prickly Pear Cactus, Opuntia ficus-indica. Journal of the American Society for Horticultural Science 117, 558–562.– An agricultural study of the Indian fig.

Drezner, T. D. & Lazarus, B. L. (2008). The Population Dynamics of Columnar and Other Cacti: AReview. Geography Compass 2, 1–29.– A review that covers columnar cacti especially the saguaro, and the impact of human activities. Also covers the history of the Indian fig a little bit.

Snyman, Hennie A. (2013). Growth Rate and Water-Use Efficiency of Cactus Pears Opuntia ficus-indica and O. robusta. Arid Land Research and Management 27, 337-348.– A study of two Opuntia introduced to South Africa at least 250 years ago. Measured that the water content of the cladodes as around 88%. In one growing season, the growth of mean fresh mass of O. ficus-indica is about 1.3 kg per cladode. Eyeballing one of its charts (omitting all the technical details), one young O. ficus-indica plant can produce easily 2 kg of dry mass per year. Consider that as 12% weight of the plant, it makes over 16.5 kg fresh cladodes (over 36 lbs). These plants have a very high water-use efficiency. And for a cactus, O. ficus-indica grows

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extremely fast.

National Park Service (2015, September 11). Saguaro Cactus Growth. Retrieved April 20, 2019, from https://www.nps.gov/articles/saguaro-cactus.htm – Information on the growth rate of saguaro.

● Related to extrafloral nectar food-for-protection mutualism

Aranda-Rickert, Adriana, Diez, Patricia & Marazzi, Brigitte (2014). Extrafloral nectar fuels ant life in deserts. AoB PLANTS 6, article plu068.– A detailed study of extrafloral nectary-bearing plants and relationships in a seasonal desert of northwestern Argentina. Has a good introduction with photos on different extrafloral-nectar secreting structures.

LeVan, Katherine E., Hung, Keng-Lou James, McCann, Kyle R.,Ludka, John T., & Holway, David A. (2014). Floral visitation by the Argentine ant reduces pollinator visitation and seed set in the coast barrel cactus, Ferocactus viridescens. Oecologia 174, 163–171.– By being aggressive, the invasive Argentine ant (Linepithema humile) is more effective in fencing off insect herbivores, but they also drive away native ant species. Areas not invaded by theArgentine ant have 18 native ant species visiting the Coast barrel cactus. The muted mutualist diversity lowers seed mass production of the cactus.

Ludka, John T., LeVan, Katherine E. & Holway, David A. (2015). Infiltration of a facultative ant–plant mutualism by the introduced Argentine ant: effects on mutualist diversity and mutualism benefits. Ecological Entomology 40, 437–443.– The presence of the invasive Argentine ant has a negative effect on floral visitation by pollinators of the Coast barrel cactus.

● News on the poaching problems

California Department of Fish and Wildlife (2018, April 6). CDFW Wildlife Officers Arrest Three for Poaching Succulents in Humboldt County. Retrieved April 20, 2019, from https://cdfgnews.wordpress.com/2018/04/06/cdfw-wildlife-officers-arrest-three-for-poaching-succulents-in-humboldt-county/ – News from the California F&W. The F&W officers arrested two Koreans and one Chinese for poaching over 2,300 Dudleya plants in Humboldt County. The overseas market value of the plants is between $40 to $50 per plant.

Carson, Erin (2018, August 29). National parks want you to stop picking them clean. Retrieved April 20, 2019, from https://www.cnet.com/news/national-parks-want-you-to-stop-picking-them-clean/ – News from cnet.com. On all the poaching problems at Saguaro National Park. The average blackmarket value for a saguaro is $100 a foot, plus another $50 to $100 for each arm.

Goodyear, Dana (2019, February 20). Succulent-Smugglers Descend on California. Retrieved April 20, 2019, from https://www.newyorker.com/news/california-chronicles/succulent-smugglers-descend-on-california – Article from The New Yorker. Two poachers pleaded no contest to felony charges for their removal of more than eighteen hundred Powdery Liveforever (Dudleya farinosa) from Garrapata

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State Park, in Big Sur. Goodyear touched on how succulents might have become so popular.

McCormick, Erin (2018, April 27). Stolen succulents: California hipster plants at center of smuggling crisis . Retrieved April 20, 2019, from https://www.theguardian.com/environment/2018/apr/27/stolen-succulents-california-hipster-plants-at-center-of-smuggling-crisis – News from The Guardian. On the extensive poaching and smuggling of Dudleya plants from California because of demands in China and Korea.

McGivney, Annette (2019, February 20). 'Yanked from the ground': cactus theft is ravaging the American desert. Retrieved April 20, 2019, from https://www.theguardian.com/environment/2019/feb/20/to-catch-a-cactus-thief-national-parks-fight-a-thorny-problem – News from The Guardian. On the extensive poaching of cacti in the Southwestern United States.To fight the poachers, rangers in Saguaro National Park have begun to embed microchips into the plants.

Smith, Sylvia (2018, September 15). Prickly cactus species 'under threat'. Retrieved April 20, 2019, from https://www.bbc.com/news/science-environment-45438733 – News from BBC News. On the plight of cacti, which includes poaching. Interestingly Smith considers that Prickly-pear (very likely meaning Indian fig) is being devastated by cochineal in southern Spain.

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