Duvalia sulcata subs. seminuda - Cactus Club

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Duvalia sulcata subs. seminuda

Plant of the Month > Species C to D

August 2017

by Bruce Brethauer

Duvalia is a distinctive group of the succulent members of the milkweed family, with approximately 20 species recognized from southern Africa,  Eastern Africa, Yemen, and Saudi Arabia.

 The following information was excerpted from The Wonderful World of Succulents by Werner Rauh:

   The genus was named by Haworth after French botanist and succulent researcher, H. Duval. It includes plants of mat-like growth with reclining or diagonally upright, usually short, seldom elongated shoots with 4 to 6 ribs and short teeth. Flowers appear singly, or in multiples and structurally differ from those of other stapeliads:
   The short corolla tube forms a thick, frequently hairy cup (= ring) that is completely filled by the outer corona, which is developed into a fleshy configuration called a coronal disk. On top of it sit the egg-shaped to spoon-shaped inner corona tips: corolla lobes ("petals") are broadly triangular, frequently, however, narrowly linear and then folded backwards.

Flowers are typically rather small, (to just under 2 inches across at the upper limit, but usually averaging about an inch across in most species), in some species, the flowers may be minute, to about 1/2 inch (or less) across.
   In most species, the flowers are reddish brown to maroon, and petals are typically fringed with tiny "club hairs" which flutter in the smallest breeze. Flowers typically produce the scent of carrion to attract flies and carrion beetles which appear to be the primary pollinators of these flowers. The scents of these flowers are not as intense as those of many of the Stapelias, and may go unnoticed unless you attempt to sniff them at close range, making them better candidates for growing in closer quarters. Out of bloom, the plants have the general appearance of a Huernia plant.

   Duvalia sulcata subs. seminuda is atypical of the genus on several counts: The stems are heavily marked in dark green to maroon, and has especially long "teeth" or "prickles" on its stem; its flowers approach the upper limits for size in this genus, topping out at just under 2 inches in some plants ( the flowers on my plant are just under 1.5 inches across ). Also, this is one of only 4 species whose range extends beyond Southern Africa, with an extended range in Yemen and Saudi Arabia. I should say at this point that there is some controversy on the 4 species whose range extends into Eastern Africa and the Arabian peninsula: genetic studies indicate that these may not be as closely allied with other members of Duvalia as once thought, and may need to be re-classified to another genus.

This subspecies differs from Duvalia sulcata in having no hairs on its annulus. The annulus of D. sulcata is covered with white hairs.

    Duvalia sulcata subs. seminuda
is an easy plant to grow, and responds well to my general guidelines for growing cacti and other succulents. My plant grows especially well during the warmer months of spring, summer and fall, when I move my plants outdoors to benefit from increased light levels, higher temperatures, and rainfall; under favorable conditions, it will produce remarkable growth at this time, and will typically produce several waves of flowers intermittently from mid-summer through the warmer months of fall. Because of its rapid growth rate during the growing season, it should be fertilized frequently at this time, probably once every 2 weeks with a dilute solution of fertilizer, or once a month with the fertilizer mixed according to manufacturers’ recommendations (full strength). I have learned that the asclepiads also will benefit from annual repotting - in part because these plants grow so rapidly that they will require a larger pot, and also because they will deplete most of the nutrients in their potting mediums. I continue to experiment with potting mediums, and most mediums which are freely draining and which will dry quickly will produce good results for a time, but I am discovering that many of the asclepiads which I am growing seem to have a preference for a medium which contains a higher percentage of sifted garden soil.

  It has also been my experience that many of the asclepiads should be frequently divided: many of these plants flower on new growth, and (in some species) on last year's growth, so for the best displays, divide the plant and repot into fresh and fertile medium to encourage lots of new growth, and good flowering. New plants can also be easily propagated from stem cuttings.
   The ideal conditions to maintain winter dormancy continues to be learning process for me, as this is when some of the asclepiads in my collection exhibit health issues. Some of my plants may have issues with stem rot, where the stems succumb to fungal infections. If you notice any issues with the stems becoming discolored or mushy, immediately cut away any affected growth, and keep a close watch on the remaining portions of the plant, and on nearby plants. It may also be a good idea to take some cuttings from healthy growth as a backup just in case the entire plant becomes affected, and has to be discarded; the cuttings may allow you to re-establish the plant again in spring. In general, during the winter months, plants should be maintained at cooler temperatures, and dryer conditions to discourage new growth; fertilizers should also be withheld at this time. Watering regimens at this time may be the key: I try to water just enough for the plants to maintain roots, about once every 3 to 5 weeks may be adequate, but if stem rot is observed, drier conditions may be indicated at this time.
Stem loss is not necessarily an indication of poor health in the succulent asclediads, even in habitat, some species ( Edithcolea grandis, for example), may experience extensive die back on older growth, sometimes producing curious "fairy rings".

   Duvalia sulcata subs. seminuda is not readily available from most sources. It is frequently carried by Bob Smoley's Gardenworld, and Miles to Go, and can probably be found on e-bay. All of the Duvalias are interesting plants, with particularly distinctive and unusual flowers. D sulcata and its varieties have some of the largest flowers, and most attractively marked stems of the group. All are smaller plants, which can easily be maintained in a 4 to 6 in pot, and while having odiferous flowers, none of these are so overpowering that they would best be excluded from the home. If you are already a collector of the succulent Asclepiads, the Duvalias should be on your wish list, if you are curious, by all means, give this plant, or one of its relatives a try.


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