In arid southern California, water is a precious commodity and a limiting factor to our ever-growing populations. Much of the water that we use comes from distant places and the debates and arguments have already started over water rights and usage allotments. The time is now to start conserving our water resources and that includes cutting back on usage for our gardens and planted landscapes.
In 2002, this water deficit issue has been especially apparent because we are having the worst drought in recorded history for our region. Many of us in the horticultural and botanical fields have noted the media attention and the more common usage of phrases like 'low water use landscaping' or 'drought tolerant plants.' These categories and others pertaining to water restrictions are beginning to come into their own in our region. Whether it is mandated by city, county, or state agencies the public needs to take action in respect to water conservation due to economic and environmental impacts. It makes good sense to promote more xerophyte gardening—and we have a fantastic and diverse palette of native plant resources to chose from for our horticultural wants and desires.
Native plants of our region are natural choices for our local gardens due to their adaptive abilities to survive and even thrive in the dry conditions of our area. Unfortunately, there is still some resistance to using plants that are not 'normal' landscaping plants. Some of the basic problems currently restricting more horticultural usage of native plants include: availability of propagated materials for purchase, lack of knowledge about different species' growing needs, and a reluctance to change our current gardening practices. In respect to availability and horticultural knowledge of native plants, progress has been made. However, there is still a lot of hesitation about changing gardening practices such as altering well established irrigation regimes for our landscapes. Many native plant species will not thrive on most irrigation regimes that we presently throw on our lawns, such as heavy volume and fixed watering schedules. Most native plants need a lot less water. Many commercial landscape people have been using what they know works. However, in the past few years, this has been changing and the acceptance of more native and drought tolerant plants is slowly creeping into everyday gardening. The nursery and landscape industry is finally catching on, and these extraordinary plants are being planted by more and more people. The wide variety of native California plants, approximately 6,000 species, is about the same as what appears in the Sunset Western Garden Book. From California alone, one can find plants of all shapes, sizes, and colors as well as with different water and habitat requirements. The plants listed in this article are mostly succulents, but there are many other native xerophytes to choose from for our landscapes. Our local climatic conditions with winter rains and dry summers are shared by other regions in the world with Mediterranean-type climates such as Chile, South Africa, Australia, and the Mediterranean Basin; all of which have a vast array of amazing, xerophytic plants.
Our region—which includes Lower California, comprised of two Mexican states (Baja California [BC] and Baja California Sur [BCS]), and San Diego County—is well known for its botanical diversity. These areas are rich in plant species due to their varied topography, geology, and weather regimes. These factors, in addition to the region's biogeographic history, have resulted in a wide range of vegetation types that include coastal sage scrub, chaparral, conifer forest, and various desert communities. The Baja California peninsula and its adjacent islands support a wealth of species diversity that is estimated to have more than 4000 plant taxa (species and infraspecific categories, including varieties and subspecies). San Diego County also has its claim to fame and boasts the greatest floristic diversity of any county in the continental United States. The county contains over 2000 different plant species and more are being found all the time. At present, San Diego County's documented flora consists of 2,154 plant taxa, of which 473 are considered non-native and naturalized (Simpson and Rebman 2001).
Cylindropuntia bigelovii var. bigelovii (pictured above), often called the Teddy-bear Cholla, but is anything but cuddly and is native to our county in the Anza-Borrego Desert State Park. If you brush against one of these plants the 'arms' break off and seem to jump on your pants or leg and are difficult to remove! Stands of C. bigelovii can form huge colonies of asexual plants that are derived from one parent. The plants are clones because this plant rarely produces viable seeds.
In both Lower California and San Diego County, many of the plant species have specialized physiological and morphological adaptations for survival in arid environments. One of the most common xerophytic adaptations throughout the world's dry areas is that of succulence in leaves and stems. These succulent plants have at least some tissues in a portion of their plant body that is modified and capable of storing large amounts of water, making the plant part appear fleshy, succulent, or swollen. For instance, the fleshy leaves of agaves, the fattened stems of cacti, or the swollen trunks of elephant trees (such as Bursera microphylla) are all obvious examples of xerophytic modifications and such plants are generally considered succulents. Classically, succulent plants are sometimes even further differentiated from other plants with fleshy leaves or stems by having the ability to use stored water reserves in their tissues and subsequently tolerate long periods of aridity, although it is sometimes difficult to discern this functional difference. Throughout the botanical kingdom, species in various plant families and genera have independently evolved the adaptation to succulence as a mechanism for conserving water and survival in arid environments. This functional modification to water-limiting conditions is just one of many morphological and physiological adaptations that can be found in various plant species from different deserts and different ancestries, often resulting in such convergence as the overall similarities of African euphorbias and New World cacti. It is estimated that there are approximately 10,000 succulent plant species throughout the world, with most of these found in the Agavaceae, Aizoaceae, Asclepiadaceae, Asphodelaceae (Aloeaceae), Cactaceae, Crassulaceae, Euphorbiaceae, and Portulacaceae (Oldfield, 1997).
The arid portions of Lower California illustrate this diversity. It is estimated that this region has a total of 301 taxa (261 species) in 27 different vascular plant families which can be regarded as leaf or stem succulents (Rebman 2001). Some of the plant families with succulent members in the region include: Aizoaceae, Anacardiaceae, Asteraceae, Bromeliaceae, Burseraceae, Cucurbitaceae, Fouquieriaceae, Nolinaceae, Nyctaginaceae, Solanaceae, and Vitaceae. However, the highest diversity of succulents in Lower California can be found in five plant families: Cactaceae (129 taxa), Crassulaceae (38 taxa), Agavaceae (26 taxa), Portulacaceae (14 taxa), and Euphorbiaceae (13 taxa). Furthermore, almost 65 % of all the known succulents in Lower California can be found in three families: Cactaceae, Crassulaceae, and Agavaceae. In these three most diverse succulent families, the percentage of taxa endemic to Lower California is also very high. The Agavaceae have the highest percentage of endemism among these families, with 84.6 % or 22 endemic plant taxa. The Cactaceae have 92 endemic taxa (71.3 % endemism) and the Crassulaceae have 26 endemic taxa (68.4 %). A few endemic, succulent genera can also be found in the Lower California region, including: Pachycormus (Anacardiaceae); Baeriopsis and Coulterella (Asteraceae); Bartschella, Cochemiea, Morangaya, ×Myrtgerocactus, and ×Pachgerocactus (Cactaceae).
Most of the succulent plant species in Lower California can be divided into either stem or leaf succulents. However, some of these species, such as Cistanthe guadalupensis, have both succulent leaves and stems and can be put into both categories. In respect to the diversity of stem versus leaf succulents in the region, it is estimated that there are 184 taxa of stem succulents and 117 leaf succulents.
The most diverse group of stem succulents in Lower California is the Cactus family. The Cactaceae in this region are represented by 15 genera, 104 species, and 129 total taxa in the subfamily Cactoideae (11 genera, 71 species) and Opuntioideae (4 genera, 33 species). Of these, 71 species and 92 taxa are endemic to the region, which is a 68.3% endemism rate for species and 71.3% for total taxa. Two cactus genera (Morangaya and Cochemiea) are thought to be endemic to Lower California. Morangaya is a monotypic genus consisting only of M. pensilis, which is restricted to the mountains of the Cape Region of BCS. This genus is sometimes lumped into Echinocereus, but various types of evidence support its recognition as a separate genus (Moran, 1977). Cochemiea is composed of five endemic species; three are found on the peninsula in the central and southern portions, and two are island endemics. Some authors (Hunt, 1987) recognize this group as a subgenus of Mammillaria, but more systematic investigation is needed in order to accurately determine its taxonomic level. Various other genera, such as Bartschella (usually included in Mammillaria) and Machaerocereus (now combined into Stenocereus) were also considered endemic, or nearly restricted to, Lower California.
The most speciose genera in the Cactaceae of Lower California are Mammillaria (32 species), Cylindropuntia (19 species), Opuntia (12 species), Ferocactus (11 species), and Echinocereus (10 species). The genus Opuntia sensu lato (including Cylindropuntia and Grusonia) was considered to have the highest number of overall taxa (41) before it was split, but Mammillaria has always led in endemism with 29 endemic species and 32 endemic total taxa.
The Euphorbiaceae are represented with over 100 species in 18 genera in Lower California. Some of these species are quite succulent, especially in Euphorbia subgenus Agaloma; Euphorbia californica, E. hindsiana, E. misera, and E. xantii; plus E. ceroderma, which was not listed in Wiggins (1980) but is a very attractive succulent native to the peninsula. In the genus Jatropha there are seven species in the region, four of them endemic. Other succulent members of the spurge family found in the region include Slipper Plant/Candelilla (Pedilanthus macrocarpus) and Pimentilla (Adelia virgata), which superficially resembles the Ocotillo (Fouquieria splendens).
A wide-ranging plant family well known for its many succulent members is the Asclepiadaceae (Milkweed family). Although not very rich in succulents in Lower California, the family's diversity is represented with seven genera and 25 species, of which seven are endemic. The most succulent milkweeds in the area are in the genus Asclepias and include: A. subulata, A. albicans, and A. masonii.
The Burseraceae (Torchwood family) constitute another popular family among succulent enthusiasts and are well represented in Lower California. Although there is taxonomic research currently being conducted in order to better understand its local members, it is estimated that the family Burseraceae has eight species, including one new species not yet named from southeast of La Paz. Other sarcocaulescent or elephant tree-type species native to Lower California can be found in the Anacardiaceae or Cashew family and include Copalquín (Pachycormus discolor) and Ciruelo (Cyrtocarpa edulis).
The Fouquieriaceae have four species native to Lower California. The Ocotillo (Fouquieria splendens) is common in the northern half of the peninsula ranging to its southernmost population in the Sierra Guadalupe of BCS. The Palo Adán (F. diguetii) is more common in the southern half of the region but frequently dominates the vegetation in some parts of the Vizcaíno Desert in the central part of the peninsula. A less known member of this family is F. burragei, which looks almost intermediate in habit between the Ocotillo and Palo Adán but has white to pink colored flowers. It has a rather restricted distribution, being found only along the Gulf of California coast from the vicinity of Mulegé to La Paz and on a few southern Gulf islands. The most charismatic species in this family and perhaps of the entire peninsula is the Boojum Tree or Cirio (F. columnaris), which is common in the desert areas from El Rosario to Volcán las Tres Vírgenes. This species often looks like a large, upside-down, albino carrot and it forms forests in the southern half of BC.
The Cucurbitaceae (Melon/Squash family) have many members with succulent underground stems (tubers) or fattened lower stems (caudiciforms). One such caudiciform species in Lower California is Ibervillea sonorae, found commonly in the southern peninsula and on various Gulf islands. Other native species in the Morning Glory family (Convolvulaceae) from Lower California can be grown in cultivation so that the normally underground tuber is exposed and obvious above the soil.
The most diverse group of leaf succulents in Lower California is the Crassulaceae (Stonecrop family). This family is represented with three genera, 36 species, and 38 total taxa. The genus Dudleya is the most regionally diverse of the family, with approximately 32 species and various interspecific hybrids. Including varieties and subspecies, there are 34 taxa of dudleyas found in Lower California and 26 of these are endemic. The Stonecrop genera Crassula and Sedum, each with two species, are also represented locally.
The second most diverse group of leaf succulents in Lower California is the Agavaceae with 18 species and 26 taxa, of which 22 are endemic. This family is represented with three genera, Agave, Hesperoyucca, and Yucca. Both century plants/mescals/magueys (Agave spp.) and soaptrees/datils (Yucca spp.) are so common in some parts of the peninsula that they are obvious dominants in the vegetation. The closely allied Nolinaceae have four species in the region, all in the genus Nolina. In the USA, Nolina species are usually low-growing and called bear-grasses, but in Lower California most of the species are tree-like and are locally referred to as "sotol."
In the Bromeliaceae there are two succulent bromeliads that grow in rocky areas of the southern mountain ranges and Cape Region of BCS, Hechtia gayii and H. montana. Interestingly, H. montana seems to be a "window-leaf" plant, since the upper epidermis of its succulent leaf is transparent and the chlorophyllous tissue is on the lower side of the leaf. This apparently allows light to penetrate the upper part of the leaf, filter through the succulent portion, and then be captured by photosynthesis on the inside of the leaf. It is not known how many other succulent bromeliads also function in this manner and what advantage it confers to such aboveground rosette plants as these.
The Portulacaceae have approximately 14 succulent, or at least fleshy-leaved, species in BC and BCS. These include Calandrinia, Talinum, and various Portulaca species. The most succulent member of this family found locally is Cistanthe guadalupensis, which is both a stem and leaf succulent restricted to Guadalupe Island off the west coast of central Lower California.
The well-known succulent family Aizoaceae is also represented in Lower California but mostly by such exotics as Mesembryanthemum and Carpobrotus. However, the native species of Sesuvium can commonly be found in coastal areas of the southern peninsula.
The Sunflower family (Asteraceae) has a few succulent members in Lower California as well. Genera with at least one leaf-succulent species include Coreopsis, Coulterella, Hofmeisteria, Porophyllum, Senecio, and the endemic genus, Baeriopsis, from Guadalupe Island. Both Baeriopsis and Coulterella are monotypic genera that are considered endemic to the region.
San Diego County also has a relatively high diversity of succulents plants that are native. It is estimated that there is a total of 66 succulent taxa (64 species) in 26 genera and 14 different plant families in the county. This does not include at least three naturally occurring hybrids that also grow in the area. The two plant families that have the most succulent members within the borders of San Diego County are Cactaceae (24 species) and Crassulaceae (12 species). These two plant families contain over half of the succulent diversity that can be found in the county. Some other plant families with succulent members in the region include: Agavaceae, Aizoaceae, Asclepiadaceae, Burseraceae, Euphorbiaceae, Fouquieriaceae, Nolinaceae, and Nyctaginaceae. It should be noted that at least 14 non-native or introduced, succulent species have escaped from cultivation and naturalized in our county's native habitats. These include exotics such as Hottentot-fig (Carpobrotus edulis), Crystalline Iceplant (Mesembryanthemum crystallinum), Slender-leaf Iceplant (M. nodiflorum), Mission Prickly-pear (Opuntia ficus-indica) and Bunny-ears Cactus (O. microdasys).
For the Cactus family (Cactaceae), the following information lists the native species from San Diego County to choose from for local succulent gardening. The most diverse cactus genus in the county is Cylindropuntia, commonly called chollas. They have only recently been separated from the 'pad-leaved' (flat-stemmed) opuntias such as the prickly-pear cacti (Opuntia spp.). The chollas (Cylindropuntia spp.) for San Diego County include: C. acanthocarpa var. coloradensis, C. bigelovii var. bigelovii, C. californica var. californica, C. californica var. parkeri, C. echinocarpa, C. ×fosbergii, C. ganderi, C. prolifera, C. ramosissima, and C. wolfii. The common names for these chollas range from Buckhorn, Teddy-bear, Jumping, Snake, Cane, and Silver Cholla to Gander's, Coast, Diamond, and Wolf's Cholla. Their range in habitats, growth habits, and spination is quite spectacular. These plants make great security fences, perimeter lines, or central themes to a garden, but most chollas should be kept away from paths and children. They are beautiful, but they need respect.
Other cacti in the county are: Bergerocactus emoryi (Velvet or Golden-Club Cactus); Echinocactus polycephalus (Mojave Mound Cactus), which may be the hardest to grow outside of the desert; Echinocereus engelmannii (Engelmann's Hedgehog Cactus); Ferocactus cylindraceus var. cylindraceus and F. cylindraceus var. lecontei (both have the common name California Barrel Cactus); F. viridescens (Coast Barrel Cactus); Mammillaria dioica (Fish-Hook or Pincushion Cactus) and M. tetrancistra (Yaqui Mammillaria), are our only native mammillarias; Opuntia basilaris (Beavertail Cactus); O. chlorotica (Pancake Prickly-pear) O. erinacea; O. littoralis (Coast Prickly-pear); O. ×occidentalis (the '×' indicates a hybrid, in this case naturally occurring); O. oricola; O. phaeacantha (Desert Prickly-pear); and O. ×vaseyi. These are our native cacti, but there are other native succulent plants from which to choose.
The Crassulaceae or Stonecrop family has many succulent members and is familiar to most of us through the Jade Plant (Crassula argentea). Although the Jade Plant is not a native species to our region, it is related to our dudleyas and there is a wide range in this genus from which to choose. Local Dudleya species include: Dudleya abramsii, D. arizonica, D. attenuata ssp. orcuttii, D. blochmaniae, D. brevifolia, D. edulis, D. lanceolata, D. multicaulis, D. pulverulenta, D. saxosa ssp. aloides, D. variegata and D. viscida. Though the common names do vary, these plants are often referred to as liveforevers; this name reflects the habit of some of these plants which look like they have died, but come back every year after the first rains. There is one more species in this family that is native to our county and that is Sedum spathulifolium, the Pacific Stonecrop.
For those that are fans of milkweeds, the native and succulent asclepiads (Asclepias albicans and A. subulata) are quite interesting to behold. The stems are cane-like, about a pencil width or wider and can grow to over 2 meters tall. The interesting flowers attract an array of pollinators and the fruits produce the Milkweed family's characteristic seeds with tufts of hairs that act like a parachute to transport the seeds - that float in the air.
Though Coreopsis maritima (San Diego Sea-dahlia) in the Sunflower family (Asteraceae) has somewhat succulent leaves, its giant sister species C. gigantea (Giant Sea-dahlia) is a most interesting succulent daisy and can grow to six feet tall. These species are both drought deciduous and shed their foliage when the weather turns hot, but as the weather cools, the finely dissected leaves burst forth in a delicate display. The flowers open in the spring and can last into early summer.
The Burseraceae is famous for its legendary uses, both frankincense and myrrh are from the sap of trees in this family. In our local Anza-Borrego Desert State Park we have one member of this family, Bursera microphylla (Small-leaf Elephant Tree). It is a great shrub in cultivation, that will eventually turn into an attractive tree with time. When a leaf of this species is crushed, you will immediately realize why these plants are valued; the aromatic fragrance is splendid.
In the Spurge family (Euphorbiaceae) there is one succulent member that spans the border of Mexico and the US, Euphorbia misera (Cliff Spurge). This species makes a handsome specimen plant in a pot or in the ground. Related to poinsettias, it makes an interesting addition to any garden. There is a greater variety in this genus (Euphorbia) than any other group of succulents in the world. In fact, the African euphorbias should be looked at for many additional species in a drought tolerant garden.
Getting back to the Americas, we have our own unique plant families and one of those is the Fouquieriaceae. Here in San Diego County we have the Ocotillo (Fouquieria splendens). These plants make interesting focal points to any garden. With a little care they will grow and can have leaves throughout most of the year. Their flowers are hummingbird magnets, sure to amaze any neighborhood kids around. Another uniquely American group split off of the Lily family are the Agavaceae and Nolinaceae. Agave deserti (Desert Agave), A. shawii (Shaw's Agave), Hesperoyucca whipplei (Our Lord's Candle), and Yucca schidigera (Mohave Yucca) are all in the Agave family (Agavaceae); and Nolina bigelovii (Bigelow's Bear-grass), N. cismontana, N. interrata (Dehesa Nolina), and N. parryi (Parry's Bear-grass) are in the Nolinaceae.
To have a good selection of plants you do not have to limit yourself to regional native plants, but the point is, we do have a spectacular variety in southern California and Lower California. Using succulent plants like these listed is not only interesting, but helps conserve water and can supply natural resources for our diverse native wildlife. Hopefully, what is typical in southern California landscapes will change in the coming years and more naturalistic landscapes will become the 'norm' so that excessive water usage on our front yards will become old fashioned.
Please remember, do not take plants out of their native habitats. Purchase only plants that are nursery grown and propagated, never accept field collected specimens. You may ask how you can tell; just ask the nursery person. It is important to let them know that you care. Plants dug up from nature simply do not live long under most cultivation practices; it is a different story for those propagated in a plant nursery. At the end of this article you will find a list of a few succulent plant resources and California native plant sources. Though this article has concentrated on southern California succulents, there are many more native species available. There are also xerophytic plants that may not be succulent, but nonetheless, they make fine additions to anyone that wants to have a bit more variety to a drought tolerant landscape. Please look into using these along with succulents. Don't forget that the best time to plan a garden is anytime, the best time to plant it is in the fall. Look for help at the many local plant clubs and societies; they are a valuable resource for our area!
Hunt, D. "A new review of Mammillaria names." (reprinted from Bradleya vols. 1-5). British Cactus and Succulent Society, Oxford. 1987
Moran, R. "Qué hacer con Cereus pensilis?." Cactáceas y Suculentas Mexicanas 22: 27-35. 1977
Oldfield, S. "Cactus and Succulent Plants - Status Survey and Conservation Action Plan." IUCN/SSC Cactus and Succulent Specialist Group. IUCN, Cambridge, UK. 1997
Rebman, J. P. "Succulent diversity in Lower California, Mexico." Cactus and Succulent Journal (U.S.) 73: 131-138. 2001
Simpson, M. and J. Rebman. "Checklist of the vascular plants of San Diego County, third edition." SDSU Herbarium Press, San Diego. 2001
Wiggins, I. "Flora of Baja California." Stanford University Press, Stanford, CA. 1980
Below is a brief list of sources for ideas and plants in southern California, especially in regard to native and succulent plant species.
San Diego Botanical Gardens (formerly Quail Botanical Gardens)
Succulent and Cactus Nurseries
Native Cacti and California Plants
Local Cactus and Succulent Clubs
If you want to look for a club near you, take a look at:http://affiliates.cssainc.org/cssa-affiliates-united-states.html for a list of affiliated clubs in the Cactus and Succulent Society of America (www.cssainc.org)