Duvalia is a genus of succulent plant in the family Apocynaceae. The genus was first described in 1812, named after the French physician and botanist Henri-Auguste Duval. The majority of the species are restricted to the western part of South Africa and Namibia, with the greatest number of species occurring in the Great Karoo region, on the edge of the winter rainfall area.
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Published by Daniel Mosquin on February 24, 2014
A thank you to Taisha, who again writes today’s entry:
Duvalia polita, commonly known as the polished star, was first described by N.E. Brown. The photos (originals: close-up and habit) were taken last month by Bart Wursten (aka [email protected]) on a recent trip through Zvishavane and Bulawayo in Zimbabwe. Bart encountered many of these small plants–thanks for sharing, Bart!
Fleshy-stemmed, Duvalia polita is a succulent member of the Apocynaceae. Dogbane family members with this morphology form a group collectively known as the stapeliads. Stapeliads are found exclusively in the Old World in semi-arid to arid areas. Duvalia polita itself is native to dry regions of southern Africa. Plants form clumps among trees or low bushes the species is often associated with Colophospermum mopane woodland.
The polished star is a small species, with its succulent stem rarely exceeding 10cm in height. Slender leaf-rudiments are held on the stem, but these quickly dry out and wear off. The inflorescence sits near the base of the stem. Green on the outside, the corolla is shiny and purple-brown on the interior, with a lighter annulus mottled with cream. The inner and outer corona lobes surround the gynostegium (the collective term for the staminal column and style head). Within the gynostegium are two carpels, each with unilocular ovaries but with one common style. The five guide rails are the receptive structures for the pollen and are distributed around the style head. The pollen is massed in pollinia, which join to form pollinaria. Five of these also surround the style head.
According to Peter V. Bruyns in volume I of Stapeliads of Southern Africa and Madagascar (2005), these deceivingly complex flowers attract flies as pollinators (a carrion scent is given off by the corolla lobes and annulus). Scurrying around on the corolla, a fly will potentially catch a leg or its proboscis in the guide-rail and then further into the corpuscle of the flower. In attempting to free itself, the fly will often remove a pollinarium. After dislodging itself, the fly might make its way to another flower and repeat the process. This time, though, the pollinia may connect to the guide-rail and be secured by the insertion-crest of the pollinia. When the fly tries to jerk itself away, the pollinia will remain stuck to the guide-rail, leaving the pollinarium adhered to the fly. The nectar behind the guide-rail stimulates pollen germination and the tube grows through the insertion-crest and into the style head.
With little success, I tried to find a good diagram of stapeliad floral morphology for a better understanding of the pollination process. Instead, I offer a book preview of the Illustrated Handbook of Succulent Plants: Asclepiadaceae, by Albers and Meve, where on pages 5 and 6 a couple of illustrations may be of help!
Origin and Habitat: Republic of South Africa (Eastern Cape).
Habitat and ecology: The same area harbours many other succulents such as Haworthia cooperi, Haworthia nigra, Euphorbia tridentata, Stapelia miscella and various Senecios.
Description: The "modest duvalia" or "unassuming duvalia" (Duvalia modesta), is a mat-forming, perennial-succulent, with briefly egg-shaped stems with 4 to 5 indistinctly hooked ribs. The dark chocolate petals of D. modesta are bent backward for one-half their lengths, bent into a hook and have their edges fringed with purple hairs. The flowers, two to tree occur in the middle of the younger stems. The annulus is naked the coronal disk is bluntly pentagonal and flesh colored.
Derivation of specific name: We can only assume that this plant was called the 'unassuming duvalia' because of the smallness of its flowers which are about 1.5 cm across, (modesta meaning 'unassuming') .
Stems: Delicate, 12-40 (or more under cultivation) mm long, 8-12(-20) mm thick, ovoid or oblong (to cylindrical), with 4–5 obtuse tuberculate-toothed angles, glabrous, dark green.
Leaves: Rudimentary 1.5 mm long, stipular glands small, some-times absent.
Flowers: 2–3 (or more) together at the middle of the young stems, procumbent, developing successively with slight foetid odour. Pedicels 8-20 mm long, glabrous. Sepals 2-4 mm long, lanceolate, acute, glabrous. Corolla 12-25 mm in diameter, dark chocolate to brownish-purple. Corolla lobes 5-9 mm long, 3-6 mm wide, with the margins closely replicate at the apical half and reflexed-spreading at the basal part, ovate when flattened out, acuminate, margins ciliate for half of their length with soft fine, often curved, simple purple hairs 1-2,5 mm long, otherwise quite glabrous. Annulus about 5-8 mm in diameter, 1-1.5 mm high, circular or obtusely pentagonal, glabrous, rim papillose, hairy papillae 0.05 - 0.1 mm long. Corona ivory, maroon, brown to dark purple, disc 3-5.5 mm in diameter, obtusely pentagonal, mostly dark reddish-brown. Inner corona-lobes 1-2 x 1-1.5 mm mostly reddish. Pollinia 0.3 x 0.2 mm.
Fruits (paired follicles): 8 - 13 cm long, fusiform.
Seeds:* 4x 2.5 mm.
Bibliography: Major references and further lectures:
1) N. E. Brown “Flora Capensis”, Vol 4, 1909
2) Werner Rauh “The Wonderful World of Succulents: Cultivation and Description of Selected Succulent Plants Other Than Cacti” Smithsonian Institution Press, 1984
3) Focke Albers, Ulrich Meve “Illustrated Handbook of Succulent Plants: Asclepiadaceae: Asclepiadaceae” Volume 4 Springer, 2002
4) Bruyns, P.V. “Stapeliads of southern Africa and Madagascar.” (Vol. 1, pp. 1-330). Umdaus Press, Pretoria.2005
5) Thomas H. Everett “The New York Botanical Garden Illustrated Encyclopedia of Horticulture”, Volume 4 Courier Corporation, 01 January 1981
6) “Bradleya: Yearbook of the British Cactus and Succulent Society”, Volumes 1-5 The Society, 1983
7) Margaret J. Martin, Peter Richard Chapman “Succulents and their cultivation” Scribner, 1978
Cultivation and Propagation: Duvalia modesta is an easy obliging blooming plant when mature, that it is happy in any average succulent house.
Potting:Since roots are quite shallow, use a soft and incoherent cactus mix or add extra perlite or pumice to regular soil potting soil, and clay pots help the plants to dry out between watering.
Waterings: Duvalia require moderately watering through the growing season but enjoy plenty of water and some fertiliser in hot weather, this helps them to flower freely. Water more sparingly in winter according to temperatures. But, as with most asclepiads, it is unwise to leave them wet in cold weather.
Fertilization: Fertilizers for succulent plants must be rich in potassium, but poor in nitrogen, to avoid the plants from developing excess vegetation, which is easily attacked by fungal diseases.
Sun Exposure: As with many succulents, they prefer to grow in the light shade of scrubby shrubs or between rocks where they get some shade during the day. In summer it is advisable to position this plant in a partially shady place, where it is exposed to direct sunlight only during the coolest hours of the day.
Hardiness: These plants don't like cold weather, therefore in the Spring it is best to set them outside only when the temperatures are above 15°C. Can endure temperatures below 5°C for short period, but only if the soil stays completely dry.
Pest and diseases: Duvalias vary in their susceptibility to rotting, but are generally fairly easy to grow, especially if kept pest-free. They are very susceptible to stem and root mealy bugs, and damage from these may well initiate fungal attack. If you do have problems with a stem or with basal rotting, you can reliably isolate the healthy parts, dry them off, and re-root them in moist compost.
Cultural Practices: Re-pot every 2 years.
Propagation: Easiest with stem cuttings. Allow cuttings to dry a day before planting. Stems must be laid (Not buried) on gritty compost and will then root from the underside of the stems. It can also be increased from seeds sowing in spring in moist, sandy peat moss. Barely cover seeds. Seeds germinate quickly.
UF/IFAS Duval County Urban Gardening Program manages one community garden on City of Jacksonville property at our Superior Street Demonstration Garden location. If you don’t have adequate space to grow vegetables at your home, or if you are looking for new gardening friends with whom you can learn and improve your gardening skills, renting a community garden plot might be for you.
Plots are available for rent to all Duval County Residents on a first-come, first-served basis. Gardeners sign a rental agreement and are able to grow vegetables, culinary herbs and edible flowers for family (non-commercial) use. If you would like to inquire about plot availability, please contact Beth Marlowe at 904-255-7450 or [email protected]
The Urban Gardening Program assists other community gardens throughout Jacksonville with education and technical assistance to help them grow successfully. If you are interested in starting a community garden, or renovating an existing garden, please contact Beth Marlowe at 904-255-7450 or [email protected] We can help with all phases of setting up and maintaining your community garden, including such things as:
• Garden & Irrigation Design Guidance
• Identifying Grant Opportunities
• Raised Bed Construction Guidance
• Irrigation Installation Guidance
• Limited Site Preparation (Tillage)
• Seed and Transplant assistance
• Pest, Disease and Nutrient Deficiency Identification
• Integrated Pest Management
There are a number of resources available online for those interested in starting a community garden. Below is a selection of documents that may be particularly helpful for gardeners in Duval County.
• Community Garden Regulations
For more information about the Urban Gardening Program or Community Gardening, contact Beth Marlowe by e-mail or phone at 255-7450
For general vegetable gardening questions contact a Master Gardener Monday through Friday from 9AM to noon and 12:30 PM to 3:30 PM by phone at (904)255-7450.