False tillandsia (Aechmea recurvata variegata ‘Aztec Gold’). (Courtesy Tom Karwin)
Coral cactus (Euphorbia lactea ‘Cristata’). (Courtesy Tom Karwin)
Leatherleaf plant (Graptopetalum ‘Purple Delight’). (Courtesy Tom Karwin)
Giant oxalis (Oxalis gigantea). (Courtesy Tom Karwin)
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False tillandsia (Aechmea recurvata variegata ‘Aztec Gold’). (Courtesy Tom Karwin)
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The Monterey Bay Area Cactus and Succulent Society recently held its holiday party. Society members create this annual event, which includes a time for members and their guests to socialize and enjoy a volunteer-created catered luncheon.
The event features opportunities for participants to acquire plants from a raffle, a silent auction and an active auction.
These three activities included an impressive plant array and allowed enthusiastic participants to share their plants and acquire appealing new additions that provide interesting, sometimes architectural forms and a range of colors.
At the event, I acquired four plants for my garden and renewed my absorption in the dazzling world of succulents. This column includes descriptions of these plants and an overview of succulent plant diversity.
Today’s image gallery
The accompanying snapshots focus on four plants I acquired at this event, still in their containers. These plants, like others at the event, are not in bloom at this time of the year. Still, this spontaneous gathering of plants represents a glimpse of the diversity of succulents. We will install them promptly to complement the thematic plant groupings in my garden.
What are succulent plants?
Succulents are not a taxonomic category but are known botanically as having succulence, a characteristic that Wikipedia describes as “plants with thickened, fleshy, and engorged stems and or leaves, to retain water in arid climates or soil conditions.” A greatly thickened stem, called a caudex, occurs on several plants. View an online list of plant families with caudiciforms at bihrmann.com/caudiciforms/fami/fami.asp.
Some definitions of succulent plants also include water-storing underground organs, such as bulbs, corms and tubers. Those definitions include geophytes in the succulent category, although many horticulturists regard geophytes as a separate category.
Cacti also store water in their stems or leaves, and botanists list them as succulents, but most horticulturists regard cacti as a category separate from succulents. This distinction might reflect the fact that cacti are native only to the Americas, even though some old-world plants called succulents have evolved to resemble cacti. Examples include some Euphorbia species.
In addition to water-retaining fleshy stems, leaves or underground organs, succulent plants can have other water-saving features. One example is a waxy, hairy or spiny outer surface. To dig deeper into these interesting features, visit Wikipedia and search for “succulent plant.”
The diversity of succulent plants
Some 60 plant families contain succulent plants, including genera with both succulent and non-succulent species. A great number of succulent species exist, including an increasing number of natural varieties and intergeneric and cross-generic hybrids.
Succulent plants can be found on all continents except Antarctica. As noted above, these plants develop in arid climates, but do not appear in extremely dry areas, such as the Great Australian Desert, South Africa’s Saharan Desert and Chile’s Atacama Desert.
Differences across plant families lead to many forms of succulent plants, including rosette forms, which our recent column focused on, as well as too many others to list here.
To review the distribution of succulent plants across plant families, visit Wikipedia, search for “succulent plant” and scroll to “Families and genera.” You will find the plant families with the most succulent genera.
Many succulent plants will thrive in the Monterey Bay area’s moderate climate. Here are some genera: Agaves (many species); aloe spp. (hardy types like aloe striata); echeveria, graptopetalum, sedum (mostly the hardy species); opuntia spp. (prickly pears); crassula spp. (most); and dudleya (California native rosette succulents).
Some succulents are not suitable for outdoor gardens. Here are the conditions under which succulent plants require protective care, with examples: heat-loving: desert rose (Adenium obesum); frost-tender: Easter lily cactus (Echinopsis oxygona); high humidity: living stones (Lithops spp.); and extreme dryness: some Mexican cactus species (Turbinicarpus).
Succulent additions to my garden
False tillandsia (Aechmea recurvata variegata ‘Aztec Gold’). This South American bromeliad grows to a mature size of 1 to 2 feet tall and wide, with glossy, yellow-green, arching leaves and small spines. In the spring, its inflorescence emerges from a thorny, red crown and presents orange-red bracts and pink to violet blossoms. It can grow in bright shade, but I will place it where it will have full sun exposure to develop its best colors. I will group it near my other bromeliads to support comparisons within this plant family. The generic name comes from the Greek word for “spearhead.”
Coral cactus (Euphorbia lactea var. cristata). This unusual succulent has various patterns and colors, and the crested form has wavy paddles that are fuller than the basic form. Native to India and Sri Lanka, this tropical succulent is a member of the spurge family (Euphorbiaceae). The specific name refers to the plant’s milky-like toxic sap. Because this variety does not grow roots well, it is often grafted onto the base of a host plant (Euphorbia neriifolia), where it grows to a height of 16 inches. In their natural habitat, uncrested species can reach 15 feet in height. It flowers only rarely in the wild, so this specimen will be valued only for its uncommon appearance. I haven’t decided where it might belong in my garden.
Leatherleaf plant (Graptopetalum ‘Purple Delight’). This elegant succulent is an intergeneric hybrid of G. amethystinum (jewel-leaf plant) and G. paraguayense (mother-of-pearl plant). This member of the stonecrops plant family (Crassulaceae) is native to Mexico. It produces 4-inch-wide rosettes that range in color from deep lilac and pinkish red to frosty white. The rosettes’ stems rise to 10 inches, then become decumbent and produce aerial roots that reach into the soil. The plant evolves during its growth cycle, providing a slow-motion drama to observe in the garden. I will add this plant to my Mexican succulent bed.
Giant oxalis (Oxalis gigantea). Gardeners often work to remove the weedy oxalis species, called the Bermuda buttercup (Oxalis pes-caprae), but that species is just one of 500-plus members of the wood-sorrel plant family (Oxalidaceae). The giant oxalis, native to Chile, grows to 8 feet tall with slender, woody stems bearing numerous leaves less than half an inch long. The small leaves are a water-saving feature of this succulent plant. The stems can develop erectly, then become curved and drooping, forming a complex shape that the gardener can control with care. In the spring, the plant develops bright yellow, 1-inch-wide flowers. This plant is destined for my Chilean plant bed.
This week in the garden
Explore the diversity of succulent plants.
Tom Karwin is a past president of Friends of the UC Santa Cruz Arboretum and the Monterey Bay Iris Society, a past president and Lifetime Member of the Monterey Bay Area Cactus & Succulent Society, a Lifetime UC Master Gardener (certified 1999-2009), past board member of the Santa Cruz Hostel Society and a current member of the Pacific Horticultural Society and other garden-related societies. To review the archive of recent On Gardening columns, visit santacruzsentinel.com and search “Karwin.” Visit ongardening.com to review columns from 2012-2020 (and eventually) from the following years. Please send comments or questions to gardening@karwin.com via email.
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