Dudleya

Dudleya, commonly known as liveforevers, is a genus of rosette-forming succulent plants in the stonecrop family, Crassulaceae, consisting of about 68 taxa in southwestern North America and Guadalupe Island. The species come in many forms, some large and evergreen, others geophytic and deciduous. Yet, despite their dramatic variations in appearance, most species readily hybridize. The flowers of Dudleya have parts numbered in fives, with the petals arranged in tubular, star-shaped, and bell-shaped forms and, when fruiting, are filled with tiny, ovoid-crescent-shaped seeds.
The genus evolved as neoendemics, from ancestors in the stonecrop genus, Sedum. The ancestors radiated southward from Sedum during the creation of the dry summer climate, in the California region, five million years ago. Early botanists classified the larger species as Echeveria and Cotyledon, while the geophytic species were placed under Sedum. Taxonomic efforts, started by Joseph Nelson Rose and Nathaniel Lord Britton, created three genera; these initial genera were all eventually subsumed into Dudleya, proper, following Reid Moran's investigations into the genus. Phylogenetic research is still at an early stage in the genus, and is complicated by the fact that many species are becoming endangered and over-harvested (poached).
Dudleya is a relatively obscure genus, in comparison to other, more widely-cultivated succulents; converging interests, by succulent collectors, native plant enthusiasts and gardeners alike, have led to the wider cultivation of many species as ornamental plants. In the wild, many species of Dudleya are vulnerable, as land development and poachers often threaten particularly niche populations of plants. Poached plants are often shipped to East Asia, especially South Korea, where hybridisation and cultivation of succulents is very popular. Conservationists, nurseries and governments combat Dudleya poaching through propagation programs and protection laws.
This genus is the only taxon of the Sedeae tribe to have evolved sympodial branching.
The genus is traditionally divided into three subgenera, two of which were formerly their own genera. The subgenera consist of Dudleya, Stylophyllum, and Hasseanthus.
One of the most famous features of some Dudleya is their waxy coating. Numerous species have their foliage covered in an epicuticular wax, or farina. This waxy coating is usually white, chalky, and mealy, and is the namesake in many epithets, like chalk dudleya, powdery liveforever, and giant chalk dudleya. The wax on the giant chalk dudleya is a surface with some of the highest ultraviolet reflectivity ever discovered in plants. When exposed to water, the wax may coat drops on leaves, preventing their evaporation. The farina is mostly composed of pentacyclic triterpenoids.
Other members, such as D. viscida and D. anomala, have a clear, sticky layer on their foliage. This adhesive layer ultimately helps the plant protect its leaves from the sun, much like ones with "white" wax. It accomplishes this solar protection by allowing dust to adhere to the sticky layer on the leaves, which coats the foliage with dust and debris, blocking solar radiation.
The earliest species of the genus described was Cotyledon caespitosa, by Adrian Hardy Haworth in 1803, which would later be known as Dudleya caespitosa. The same species would later be described again as Sedum cotyledon by Joseph Franz von Jacquin in 1811, and in 1840 Thomas Nuttall described both Echeveria pulverulenta (Dudleya pulverulenta) and Echeveria lanceolata (Dudleya lanceolata). The differing generic placements of these early descriptions suggest that taxonomic disagreements over the genus had an early start, with some of these generic placements persisting even after the proper description of the genus by Britton and Rose.
Nathaniel Lord Britton and Joseph Nelson Rose's revision of the North American Crassulaceae upended many of the early taxonomic classifications, with the newly-minted genus Dudleya containing 60 species, of which 41 were newly described by Britton and Rose. The two also defined the related genera Stylophyllum, which contained 12 species, and Hasseanthus, with 4 species. The primary differences between Dudleya and Stylophyllum were between the leaf shape, floral structure and petal orientation, whilst Hasseanthus was characterized by a different vegetative structure and more niche adaptations, primarily corm-like stems and deciduous leaves.
In the 1930s, Alwin Berger revised the status of Dudleya and Stylophyllum into a sectional ranking within Echeveria, while merging the Hasseanthus genera into Sedum. This was in part due to a belief that Dudleya had evolved from Echeveria radiating northward from Mexico, evidenced by the similar tubular corollas, while Hasseanthus possessed aesthetic similarities to Sedum, primarily flowers with broadly-spreading petals. Stylophyllum was believed to occupy a transitory position between Dudleya and Hasseanthus. These conclusions were widely accepted by botanists for the first half of the 20th century, until proper molecular and phylogenetic analyses began to appear.
In 1942, Reid Moran, a botanist with a longstanding interest in the genera, offered a new revision of the taxa. Moran recognized Dudleya as being distinct from Echeveria, and merged Stylophyllum as a subgenera along with Eududleya (which was changed to just subgenus Dudleya). Moran still recognized Hasseanthus as a separate genus, but realized that it was closely related to Dudleya. With assistance from cytologist Charles H. Uhl, Moran came to the conclusion that Dudleya and Hasseanthus were related closer to each other than they were to Echeveria or Sedum.
As Moran and Uhl conducted more cytological and taxonomic research on the genus, it became clear that Hasseanthus was also a subgenera of Dudleya, citing the karyological uniformity and the formation of hybrids between the genera. In contrast, while Echeveria and Sedum freely hybridize within themselves and each other, all attempts at hybridizing Dudleya with Echeveria have failed. Uhl came to the conclusion that there are probably no intergeneric hybrids with Dudleya, believing that Dudleya had split from Echeveria far enough that intergeneric reproductive success was unlikely. Despite Uhl's research, he still believed that Dudleya had evolved northward from Mexico with Echeveria, probably some time before the formation of the summer-dry climate of California, making Dudleya a paleoendemic.
Around 1993, one of the only literary treatments of the genus was written, Paul H. Thomson's Dudleya and Hasseanthus Handbook. In the book, Thompson made numerous changes and adjustments to species, and described several new species. The book included a large number of photographs, extensive descriptions, and horticultural practices for the care of Dudleya, derived from a long interest growing, visiting and collecting the plants. However, he failed to follow the International Code of Botanical Nomenclature guidelines for describing new taxa, forgoing designated type specimens, which invalidated his treatment. His treatment also contains extensive pseudoscientific material, including references to the lost continents of Atlantis, Lemuria and Mu, a belief that cosmic rays and divine intervention directly induced the chromosome counts and evolution of Hasseanthus and Dudleya, and criticism of paleontologists and the scientifically accepted age of the Earth.
Later research challenged the notion that Dudleya and Echeveria formed two distinct lineages within Echeverioideae. Joachim Thiede instead proposed that Dudleya evolved completely independently from Echeveria, evolving from relatives within the Leucosedum clade like Sedum moranii. This places Dudleya as a neoendemic that evolved recently with the formation of the summer-dry climate in California. This was evidenced by the similarities of seed-surface ornamentation between Dudleya and Sedum, which is unlike Echeveria, and the reproductive isolation between Echeveria and Dudleya.
Research in the 21st century has supported the hypothesis of Dudleya's relation to Sedum. Phylogenetic analysis has given weight to this hypothesis, concluding that Dudleya is much closer to North American members of Sedoideae than to Echeverioideae. The plant Sedum spathulifolium, which co-exists with Dudleya in Oregon and California, has been shown in multiple phylogenetic reconstructions to be a sister taxon to Dudleya, although it may not be the true sister taxon, as larger samplings are needed. Berger's hypothesis of a relationship between Hasseanthus and Sedum may still prove true, as in addition to morphological similarities, the Hasseanthus-type taxa could be basal to the genus. However, no truly conclusive evidence of significant divergence within Dudleya exists, and it remains unclear which groups are basal or derived.
The genus is named after William Russel Dudley, the first head of the botany department at Stanford University. The term liveforever may refer to the longevity and hardiness of some plants in the wild.
The name of the subgenera Stylophyllum is an allusion to the pencil-shaped leaves of the type species, Stylophyllum edule, now known as Dudleya edulis.
The name of the subgenera Hasseanthus was in honor of Dr. Hermann E. Hasse, a surgeon and collector of California flora. Dudleya virens subsp. hassei is also named after him.
The pollinators of Dudleya are mostly hummingbirds and bees, although this has been inferred in some species only from flower morphology. The genus exhibits a wide array of diverse flower varieties, even within species complexes. The flowers are mostly hermaphroditic, although some individuals may have sterile anthers. Plants with long, tubular, reddish flowers, mostly in the subgenus Dudleya, are adapted towards pollination via hummingbirds, while short, spreading, yellow flowers favor pollination by insects. Despite the evolution of long flowers towards hummingbirds, the long flowers also show no performance disadvantage in pollination environments exclusively composed of insects. While the long flowers may provide an evolutionary advantage for more effective pollination, more energy is required to produce the larger amounts of floral tissue.
The flower morphology of Dudleya also corresponds with the aforementioned groups of Hasseanthus, Stylophyllum, and Dudleya. The flowers in Hasseanthus and Stylophyllum are broad, white to yellow, and spreading, with bumblebees and bees as primary pollinators, and hummingbirds as occasional pollinators. As these species grade towards the subgenus Dudleya, the petals begin to fuse at the base, with the flowers becoming tubular and red, due to an association with hummingbird pollinators. This shift in pollinators corresponds to larger nectar volumes and higher energy contents in accordance with the demands of hummingbird pollinators.
Seed morphology also differs between Dudleya. Larger Dudleya have noticeably smaller seeds; this is likely a result of an evolutionary tradeoff. The investment in growing large allows plants to retain moisture in periods of drought, at the cost of energy placed into reproduction. Other reasons for smaller seeds may also be due to allocation of resources into vegetative reproduction via pup rosettes, instead of sexual reproduction. In contrast, the small, inconspicuous, Hasseanthus-type members produce the largest seeds in the genus. These larger seeds are not distributed very far, which contributes to the restricted ranges of the Hasseanthus subgenus.
Dudleya species are widespread and diverse in their range, but are typically found in rock outcroppings, cliff faces, or road cuts, where their leaves help them store water in a setting too dry for most types of plants. Most are small and inconspicuous when not in bloom. The two predominant habitats where plants of this genera may be found are by the coast or mountains. Dudleya favor moderate temperatures, summer dormancy, winter precipitation, and rocky habitats, which means they may be found in diverse, disjunct locales from oceanic bluffs on the California coast to sky islands in Arizona.
Regions where Dudleya can be found include The Californias, Arizona, coastal Sonora and Oregon, and southern Utah and Nevada. The diversity of species of Dudleya is centered in Southern California and northern Baja California.
In horticulture, Dudleya should be planted at an angle. This allows accumulated water to drain from the nestlike center of the plant, thus preventing microbial decay. Dudleya should not be watered from directly above, as this may damage their chalky coating known as farina, which is present on numerous species.
During the late fall to early spring period of growing, watering should be done frequently in order to promote good growth and flower development. Plants grown with exposure to rainfall, provided they are in a Mediterranean climate, they may obtain optimum moisture. In contrast, plants grown indoors or in greenhouses should be watered to ensure that the plant maximizes growth.
During the dormant period, from late spring to fall, watering should be limited to bi-weekly intervals, but not completely cut out. In nature, plants may completely desiccate themselves during the dormant period. Deciduous members of the genus in the Hasseanthus grouping should not be watered at all during dormancy.
Growing mediums should attempt to imitate the preferred soil of each species in nature. The most essential element for the medium is good drainage. Good drainage is important, as Dudleya are very susceptible to mold and fungi. How quickly the medium drains should be determined by the amount of shade in the location, which affects the rate of evaporation that the soil will go through. Thus, well-shaded Dudleya must have excellent drainage.
Fertilizers may be used to maintain good color and growth, but they should be diluted.
Clay is preferable to plastic pots when growing the plants due to the advantages with water drainage. Plastic pots may also kill the plants by overheating the roots.
Mealybugs and aphids are main pests of Dudleya. Powdery mildew has also been recorded in cultivated Dudleya.
The amount of shade a species of Dudleya requires is dependent on the location. Plants growing in coastal regions may require little shade at all, whilst plants growing in the deserts, inland valleys and mountains will require shade. The majority of plants in the genus will appreciate north-facing sites and shade during the heat of the day. During the summer months, 50% shade may be beneficial for plants. If a cold-tolerant Dudleya is grown during a freeze or snow, it should be shaded as not to damage the plant, as a quick thaw may be detrimental.
Unlike their related genera Echeveria, many Dudleya cannot be propagated through leaf cuttings. Propagation is mostly achieved via offsets, germination by seed, or in nurseries, plant tissue culture.
Dudleya seeds are crescent shaped and near-microscopic, and can be collected by taking the dried flower buds and crushing the ovules inside, which can contain hundreds of seeds. Seeds can be sown into a soilless medium, such as pumice or vermiculite, after which germination can occur within a week to 10 days.
Vegetative reproduction may occur in multiple ways:
The indigenous peoples of the Kumeyaay and Paipai region utilized the genus for both medicinal and agricultural purposes. The tender, succulent leaves were chewed on to alleviate thirst, or used to treat calluses and corns. The budding inflorescences, in their early stages, were used as food, with a sweet flavor and juicy texture. The roots were pounded up and soaked in water, used as an astringent to "tighten the gums." The roots were also boiled whole as a decoction for asthma.
Several species of Dudleya are threatened by urban development in Coastal California and Mexico, and anthropogenic-induced wildfires. However, one of the most critical threats to Dudleya species is poaching, partially caused by a demand from East Asian succulent collectors paying lucrative prices for certain Dudleya species.
The population of Verity's liveforever (Dudleya verityi), which was nearly wiped out during the 2013 Springs Fire, was targeted by poachers.
The Cedros Island liveforever (Dudleya pachyphytum) is a rare and extremely specialized Dudleya endemic to Cedros Island. In 2016, Korean nationals began moving to Bahia Tortugas, a locality in Baja California Sur, to facilitate the poaching and shipping of the plants. The species was seriously threatened after Mexican soldiers discovered poachers taking nearly 5,000 rosettes in a tractor-trailer. It was suspected the poachers rappelled onto the succulent's location via helicopter, as D. pachyphytum occupies a nearly inaccessible habitat. In 2019, the deaths and injuries of several fishermen from Bahía Tortugas who were on Cedros Island was allegedly the result of Dudleya trafficking, a conflict with the Sinaloa Cartel, or both. In 2020, the Mexican Navy in the Second Naval Region revealed that two fishermen were killed after a dispute emerged over the trafficking of the rare plant.
Bluff lettuce (Dudleya farinosa) was also targeted by poachers in numerous large-scale operations. Although not particularly rare, the size of the poaching operation pose a serious ecological threat. Starting in 2017, the U.S. Customs and Border Protection, along with the California Department of Fish and Wildlife, discovered large amounts of D. farinosa being shipped out of the country. South Korean and Chinese nationals have both been arrested in the smuggling of D. farinosa. According to nursery owners responsible for legally exporting Dudleya, buyers in Asia desired plants directly from the wild, owing to the aesthetic quality of their long caudices and weathered leaves.
The candleholder dudleya (Dudleya candelabrum), native to the northern Channel Islands, was reported to have been poached, with the thieves shipping plants to South Korea.
In response to the poaching of Dudleya, California State Assembly member Chris Ward proposed Bill AB-223, sponsored by the California Native Plant Society, which would make it illegal to poach Dudleya from state or private lands without a permit. The California Native Plant Society and conservationists have also initiated propagation programs to oversaturate the market as a means to deter poachers. On September 28, 2021, governor Gavin Newsom signed AB-223 into law.
Media related to Dudleya at Wikimedia Commons