10 minute read
Protecting Our Dudleya, California’s Star Succulent
By Christina Varnava, Living Collections Curator
If you’ve visited Santa Barbara Botanic Garden recently, you may have noticed we have a fresh display in our Arroyo Section, just south of the Entrance Kiosk. This is our new Dudleya Display, featuring 24 types of this charismatic succulent plant, with more growing in our Living Collection Nursery. Our collection of this genus has 53 taxa and is accredited by the American Public Gardens Association. To commemorate our brand new Dudleya Display and the history of our Dudleya collection, I’d like to do a deeper dive and introduce readers to a favorite genus of California succulent.
Adaptations
Dudleya spp., sometimes commonly called liveforevers, is a genus of about 65 combined species and subspecies of succulent plants. Dudleya species can be found as far west as Arizona and from southern Oregon to the southern tip of Baja California, Mexico, but most are found in California and northern Baja California. These different types of Dudleya come in different colors, sizes, and shapes, with flowers in white, red, orange, and yellow. As members of the stonecrop family (Crassulaceae), these plants are closely related to succulent garden staples like tree aeonium (Aeonium arboreum) or hens and chicks (Echeveria spp.). However, unlike tree aeonium or hens and chicks, which are native to other parts of the world, Dudleya are closely tied to the habitats and places of California — and have lots of special adaptations that allow them to thrive in the dry Mediterranean-climate summers.
Dudleya plants have incredible diversity in size and form. Some are tiny and can be difficult to spot unless they are in flower, while others are massive. For example, the Santa Cruz Island live-forever (Dudleya nesiotica) is just a few centimeters tall and is found on the coastal bluffs of its namesake island. With small yellow-green leaves that turn deep red in sunny areas, it is camouflaged well until its bursts of white flowers emerge. These flower stalks can be even bigger than the plant itself. On the other end of the size scale, there’s the giant chalk dudleya (Dudleya brittonii), which grows a massive rosette of flat, pale, gray-green leaves up to 1.5 feet (.5 meters) wide.
Dudleya are generally found in what are called “marginal habitats.” These marginal habitats are areas that are difficult for other plants to grow in, such as the edges of steep cliffs or cracks in boulders. These rugged places have very little to offer plants in the way of nutrients or access to water, but Dudleya plants have a variety of adaptations that make them perfectly suited for these conditions. The succulent leaves of Dudleya are a Swiss Army knife of drought adaptability: They can store extra water, reflect excess sunlight, combat free radicals, and keep the plant cooler.
Sunlight is vital for plants, but in dry conditions it can easily be too much of a good thing. Too much sunlight may cause the plant to lose excess water or damage plant tissues, so Dudleya have adapted many ways to protect themselves. The variable color of Dudleya leaves is not only beautiful, but also it can reveal some of these special adaptations. Many species of Dudleya turn a reddish tinge when they are grown in sunnier conditions; this red pigment is a form of sun protection. The pigment is called “anthocyanin,” and it is a type of antioxidant that helps plants to mitigate some of the harmful effects of UV exposure. Anthocyanins work to attract and capture free radicals which could otherwise cause damage to the plant’s DNA. Another form of sun protection can be seen on the very palest species of Dudleya. These striking silvery plants have leaves that are covered in a waxy substance called a “cuticle.” Their cuticle is very thick, pale, and chalky, and it functions as a powerful sunscreen. The leaves of giant chalk dudleya coated in this wax have been measured to reflect up to 83% of UV radiation they are exposed to, which helps prevent sun damage and dehydration. For comparison, leaves on the same species that do not produce this wax only reflect 10% of UV radiation.
In addition to these adaptations to protect their leaves from the sun, all Dudleya species have a special water-conserving trick up their sleeves. Dudleya can use a special process for photosynthesis to help them conserve water, called Crassulacean Acid Metabolism (CAM) photosynthesis. To learn what makes this special, you’ll need a Botany 101 crash course: As part of the process of photosynthesis, all plants must open pores on their leaves (called “stomata”) in order to take in carbon dioxide and release oxygen (figure 1). Opening these pores to allow this gas exchange is critical, but it also allows some water to escape. This process of gas exchange generally happens during the day, but when faced with drought conditions, Dudleya can shift to using CAM photosynthesis. This process is a little less efficient, but it allows them to open these pores at night when less evaporation will occur, saving precious water. Another adaptation some Dudleya have to protect against water loss is even more dramatic. One subgenus, Dudleya subg. Hasseanthus, features species that actually lose their leaves entirely in the heat of the summer. These plants have a “corm,” a type of storage organ that survives underground, even when all the above ground leaves have died off. Species in this subgenus can ditch their leaves when faced with drought conditions and lie in wait underground until the rains come to revive them and kick photosynthesis back into gear.
Ecology and Threats
Although they are uncommon, Dudleya plants are a vital part of their ecosystems. Dudleya leaves are an important food source for butterflies, hummingbirds, and other animals. For example, the Sonoran blue butterfly (Philotes sonorensis) lays its eggs exclusively on leaves of the low canyon dudleya (Dudleya cymosa ssp. pumila), which serve as a delectable meal for the newly hatched caterpillars. Dudleya flowers have almost as much variation in form as the leaves. For example, the flowers of the chalk dudleya (Dudleya pulverulenta) are narrow, bright pink, and tube shaped, with lots of nectar. All of these features are very attractive to hummingbirds. Other Dudleya have flower shapes that are more spread open. These flowers are often yellow or white and generally are more appealing to bees and other types of insects. Dudleya flowers come in a sunsettoned palette of colors that can be anything from shocking red-pink to creamy white. The flowers are held high up above the plant by an elegant arching stalk (botanists call this a “peduncle”). These sprays of colorful flowers waving high are meant to be big, bold neon signs to attract pollinators to otherwise inconspicuous Dudleya plants. The stalks are also often brightly colored as well, giving the flowers extra visibility.
One of the reasons there are so many different species and subspecies of Dudleya is because these plants tend to be tied to a very specific set of environmental conditions, which can cause populations to become isolated from one another. Once they become separate and don’t intermix with other members of the population, “genetic drift” may cause new species or subspecies to form over time. Genetic drift is the process of random mutations changing an organism’s DNA over time, which is one way new species are formed. This leads to all the marvelous differences in size, shape, form, and color that Dudleya display. Restrictions to certain types of soil, or special habitat types like cliff faces, mean that the population of a subspecies can be restricted to a very small area. This small geographic range means that Dudleya species and subspecies are more vulnerable to being wiped out by disasters both natural and anthropogenic (or, involving humans). A wildfire or a poaching operation can, of course, damage the genetic health of a species that is widespread, but with a type of plant that has a very small population, it can cause a catastrophic genetic bottleneck. These bottlenecks can reduce the ability of a species or subspecies to adapt to new environmental conditions by destroying genetic variation. Nearly half of the species and subspecies of Dudleya in California are considered rare or threatened by the California Native Plant Society. These plants are both beautiful and vital to the wild places where they grow, and we all have a part to play in their continued survival.
Help advocate for the protection of wild plants and places. The more habitat we leave intact, the more space there is for these plants to grow. You can also support legislation like California AB 223, which specifically helps address Dudleya plant poaching. You can also cultivate responsibly sourced Dudleya and encourage others to do the same.
Growing Dudleya at Home
If you want to grow Dudleya at home, you absolutely should! Be sure to buy from a trusted nursery and avoid online sellers on sites like eBay or Etsy, where poached plants may be sold. Many species are available, especially the striking and beautiful chalk dudleya (Dudleya pulverulenta). Other species that you might find include sand lettuce (Dudleya caespitosa), lanceleaf live-forever (Dudleya lanceolata), and fingertips (Dudleya edulis). To learn more about availability, check our Garden Nursery, or visit your local nursery. Another great source for both plants and information is your local chapter of the California Native Plant Society.
When you have your new, responsibly sourced Dudleya in hand, here are a few growing tips to help you succeed in keeping it happy:
• Good drainage is key. Plant yours on a slope or in a pot with a drainage hole and well-draining potting soil. Water only if the soil is very dry rather than on a specific schedule, since the weather can change how much water the plant needs.
• Just the right angle. When planting, set the Dudleya at a slight angle to help keep water from pooling at the top of the rosette. Stagnant water at the top of the rosette can cause disease. Be sure to also water the soil directly at the plants’ roots.
• Made in the shade. Most Dudleya plants like at least a little bit of shade, so plant yours where they can get some shelter from the sun in the hottest part of the afternoon. Some exceptions are the chalk dudleya which can handle full sun thanks to their special sunscreen.
• No touching! Handling Dudleya leaves can remove the cuticle, that powdery coating that acts as plant sunscreen. Avoid touching the leaves and watering from the top down.
• Enjoy. Watch your new Dudleya friend thrive and check out the insects and birds that come to visit!
