Adenium socotranum (Socotra Desert Rose)

 

Plant Family

Apocynaceae

Binomial Name

Adenium obesum subsp. socotranum (Vierh.) Lavranos

Alternate Binomial Names

Adenium socotranum Vierh, Adenium obesum (Forssk.) Roem. & Schult, Adenium obesum ssp. sokotranum.

We use Adenium socotranum as the preferred binomial name on this website to reduce confusion with other subspecies and varieties of Adenium obesum that not endemic to Socotra.

Common (Vernacular) Names

Socotra rose, desert rose, Socotra desert rose, Socotra island rose, Socotra bottle tree.  The tree has two Socotri names: tirymo (in the eastern areas) and isfid or asfid (central and western areas), the latter one meaning useless or valueless[1].

 

Plant Information

Endemicity

This subspecies of Adenium obesum is only found on Socotra, the largest island in an isolated archipelago of the Republic of Yemen located south of the Arabian Peninsula in the Indian Ocean.  The island has a dry desert climate with strong monsoonal winds.  Most the island consists of limestone and its soils are infertile, clayey and alkaline.  The plant grows in gravelly, well-drained soil and limestone rock formations.  It is widespread on the plains and limestone plateau, and often abundant in on rocky foothills and escarpments.  It is found at sea-level and into semi-deciduous woodland at higher altitudes on the hills[2].

 

Adenium socotranum at Socotra Island seashore

Adenium socotranum at Socotra Seashore
Photo attribution: Eternal Yemen Tour Operator   

          
Adenium socotranum on plains area of Socotra island

Adenium socotranum at Socotra   Island Plains
Photo attribution: Eternal Yemen Tour Operator

          
Adenium socotranum on Socotra Island Hillside

Adenium socotranum on Socotra Island Hillside
Photo attribution: Eternal Yemen Tour Operator

Growth Habit

Adenium socotranum is the largest member of the Adenium genus and known for its bizarre appearance.  Mature plants growing in the wild typically have an enormous pachycaul trunk, and a few short branches extending from the top of the plant with sparse vegetation. (The word ‘pachycaul’ is derived from the Greek: pachy- meaning thick or stout, and Latin caulis- meaning the stem). The wild form of the plant varies with differences in wind patterns and other local conditions at the areas on the island where it grows.

The species has several adaptations to the harsh climate:

  • Minimal waxy leaves and the greatly reduced surface to volume ratio resulting from the globular or columnar shape of the plant minimizes water transpiration.
  • The plant has the capacity to store large amounts of water in the caudex between infrequent rains and fog events.  The poisonous, latex-like sap discourages predation.
  • A sap cycling system within the caudex prevents overheating and micro-anatomical epidermal protrusions reflect solar radiation.

Socotra roses are very slow growing, and mature plants in the wild may be several hundred years old.  In cultivation, our seedlings have reached a maximum height of about one meter after several years.  Seedling growth rates are highly variable under identical growing conditions and most our specimens of this age are much shorter.     We want to grow our plants in their natural form and do not prune them or trim their roots.  Most of our seedlings consist of a single shoot extending upward from the top of the caudex.  We believe the plants will continue to grow in this manner until reaching a maximum height and then the caudices will begin to fill out and eventually comprise most of bulk of the plant.

Leaves are arranged in dense terminal rosettes.  At our nursery location in Discovery Harbour, Hawaii our Socotra roses typically lose most their leaves during the early spring but many retain some leaves throughout the year.

Leaves of Adenium socotranum

Leaves of Adenium socotranum
In cultivation at Discovery Harbour, Hawaii
Photo © Edward Rau, Sustainable Bioresources, LLC
Use License CC BY-SA

 

Caudices.  The most prominent feature of the plant is its above ground caudex that can grow up to 2.5m in diameter and 3.5m high in the wild.  Caudices of immature plants in cultivation are typically conical but globular forms are also common.  The caudex has vertical striations of varying intensity.   Unlike related species of Adenium, the seedlings begin development of the caudex early and as the seedlings reach about 10cm in height the caudex is predominant and comprises the bulk of the plant.

Young seedling of Adenium socotranum

One Year Old Seedling of Adenium socotranum
Photo © Edward Rau, Sustainable Bioresources, LLC
Use license CC BY-SA

Caudex of Adenium socotranum seedling

Caudex of Adenium socotranum
Growing at Discovery Harbour, HI
Photo © Edward Rau, Sustainable Bioresources, LLC
Use license CC BY-SA


Adenium socotranum, seven year old leafless seedling in bloom

Seven Year Old Seedling of Adenium socotranum 
Photo © Edward Rau, Sustainable Bioresources, LLC
Use License CC BY-SA

 

 

Flowers.  Two of our seedlings began to bloom when they were about seven years old; all the others have not bloomed.  The typical age for first blooms in cultivation is reportedly about ten years.  Here they began to bloom in April of 2017 and continued into mid-May. The flowers are pink and borne at the tops of the plants, which may be leafless or have only several leaves present.

Flower Buds of Adenium socotranum

Flower Buds of Adenium socotranum
Growing at Discovery Harbour, Hawaii in April 2017
Photo © Edward Rau, Sustainable Bioresources, LLC
Use license CC BY-SA

Flower of Adenium socotranum

Flower of Adenium socotranum
Blooming at Discovery Harbour, Hawaii in April 2017
Photo © Edward Rau, Sustainable Bioresources, LLC

 

Seeds.  Seeds form in two opposing horn-like pods typical of members of this plant family.  Upon ripening they spilt open releasing the seeds.

 

Uses

We began growing Socotra roses as specimen materials for research and educational purposes.  Excess plants are sold to help fund our research activities.

Bonsai and Ornamental.  Hybrids of this species are widely used for bonsai subjects.  Socotra roses may also have applications as specimen plants for use in xeric tropical landscaping but their very slow growth, rarity and cost currently precludes significant use.  We grow only the pure species, no hybrids.  Please refer to this instruction sheet for recommendations on growing our Socotra roses.

Medicinal Uses.  The white sap from the stem of the plant is widely used in Socotra for medicinal purposes including treatment of malarial fevers, skin diseases and swollen injuries[3].  Recent biomedical research has found in vitro anti-influenza virus[4] and antineoplastic[5],[6],[7],[8],[9],[10],[11] activities in plant extracts.  In 2016, we submitted specimens of our plants to the College of Pharmacy at the University of Hawaii to be screened for antineoplastic and antimicrobial activity.

 

Cultivation

This plant has been very rare in cultivation as the pure species.  Hybrids and many cultivars are common.

We attempted to grow several seedlings of this plant in native volcanic soils at our nursery site. Dolomite and limestone was added to the planting areas to raise the pH, provide more calcium and magnesium, and better simulate the soil conditions of Socotra island.  The plants were observed for about three years.  During most of this time they failed to grow and were devoid of leaves throughout most of the year.  One plant rotted and the remaining plants were removed and transplanted in pots containing a mixture of local cinder soil and dolomite limestone additives.  After several months, the plants began to grow but much slower than plants that were originally planted in pots.  We have observed similar results with multiple other species of drought adapted deciduous plants such as Moringa and Pachypodium –  they remain dormant and fail to grow when planted in local soils without irrigation but thrive when planted in outdoor containers of the same soil.  These plants are adapted to drought and go dormant when soil conditions become xeric.  While we have much more rain here than in the areas where they are endemic, the rapid fluctuation in soil moisture in our highly pervious volcanic soil and onset of xeric soil conditions between rainfall events may keep the plants in dormancy.  In pots and irrigated soil the plants do not experience xeric conditions triggering dormancy.  This is speculative but seems to best fit our observations.

When we moved our collection of this species from our Maryland greenhouse facility to Hawaii we kept them in a greenhouse because we concerned about the potential for adverse impacts from excessive rainfall on the plants.   The rainy season in Hawaii overlaps the typical period of dormancy for the species.  In Maryland, we did not water the plants when they were leafless and presumably dormant.

Collection of four year old Socotra rose seedlings grown at Discovery Harbour, Hawaii

Collection of Four Year Old Socotra Rose Seedlings
Grown at Discovery Harbour, Hawaii
Photo © Edward Rau, Sustainable Bioresources, LLC
Use licensed CC BY-NC

We and other growers of this and related species have previously recommended use of rapidly draining, inorganic soil media, minimal watering and planting in shallow pots to simulate growing conditions like those of Socotra island.  In part by experimentation and mostly by accident we have found that the plant is not fastidious and the previous recommendations were not optimal.  It grows best outdoors, with water year-round and faster growth occurs in larger pots with deeper soil.  In well-draining cinder based soil with some organic amendments it tolerates wet soil conditions over periods of several weeks even when dormant.

 

Propagation

This species is most commonly grown from seed but can be propagated from cuttings.

 

Improved Cultivars

We are not aware of any development of cultivars of the pure species.  Numerous hybrids of this and other adenium species have been developed.   They are very popular, particularly in Thailand for bonsai and ornamental uses.  These are adapted to growing in artificial cultivation with ample water and frequent fertilization.

 

Pests and Diseases

No pests or diseases have been reported in plants growing in the wild.  Our plants are not affected by the airborne anthracnose fungus or pathogenic soil nematodes known to be present in soils at our nursery site.

When grown outdoors here in Hawaii our plants occasionally have some minor infestations of aphids and scale insects on the leaves.  Aphid infestations usually resolve without intervention but can be treated with insect soap or neem oil.  Plants grown outdoors are occasionally infested by scale insects, which are spread and tended by yellow crazy ants Anoplolepis gracilipes, a highly invasive species.  These infestations are more difficult to control and may result in defoliation of the plant if left untreated.

Yellow Crazy Ant Anoplolepis gracilipes at Discovery Harbour, Hawaii

Yellow Crazy Ant Anoplolepis gracilipes
Discovery Harbour, Hawaii
Photo © Edward Rau, Sustainable Bioresources, LLC
Use licensed per CC BY-SA

Yellow crazy ants (Anoplolepis gracilipes) tending scale insects

Yellow Crazy Ants Anoplolepis gracilipes
Tending Scale Insects on Adenium socotranum
Discovery Harbour, Hawaii
Photo © Edward Rau, Sustainable Bioresources, LLC
Use licensed per CC BY-SA

Yellow Crazy Ant Anoplolepis gracilipes feeding on scale insects

Yellow Crazy Ants Anoplolepis gracilipes
Feeding From Scale Insects on Adenium socotranum

Discovery Harbour, Hawaii
Photo © Edward Rau, Sustainable Bioresources, LLC
Use licensed per CC BY-SA

 

Plants grown indoors are prone to attack by spider mites and scale insects, particularly when grown under adverse growing conditions of high humidity, cooler air temperatures and poor air circulation.  Mealy bugs can also infest plants grown indoors and may attack the roots.  Root infestations may jeopardize the plants if not treated.  Highly granular planting media, often recommended for growing adeniums, probably facilitates mealy bug access and proliferation on the roots.  We routinely incorporate some diatomaceous earth in the planting media, and this appears to be effective in preventing mealy bug infestations of the roots.  Severe mealy bug infestations of other Adenium species grown outdoors are apparently common in Hawaii; we have not observed this on our Socotra roses.

We have had good results in using imidacloprid soil drenches to provide long term control of ants and other insect pests on Adenium socotranum.  Given the rarity and high value of these plants such treatments may be advisable as a preventative measure.

 

Invasiveness Potential

We requested the Hawai‘i-Pacific Weed Risk Assessment (HPWRA) program to assess the invasiveness potential of this species since there were no records of prior introductions in Hawaii.  HPWRA assigned it an assessment score of -8, indicating very low risk.  It has been designated as a Pono Plant, a good choice for planting in Hawaii.

 


Conservation Status

Adenium sokotranum is abundant on Socotra island and categorized by the ICUN Red List of Threatened Species as a species of Least Concern (LC).  The current population trend is unknown.2  Socotra’s ecosystems are undergoing increasing pressures from unsustainable resource use, loss of traditional land use management, illegal trade in biota and other factors typically affecting other global insular ecosystems[12].

 

CITES Listing

Trade in Adenium socotranum is not regulated under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

 

Plants and Seeds for Sale

Availability

Until recently specimens of wild types of the pure species were rarely available in commerce.  Some nurseries are now producing seedlings but larger plants take several years to grow and remain scarce.

Seeds.  Seeds are not available from us and export from Socotra is restricted.  Our plants began to bloom  in 2017 and may produce seeds.

Nursery Stock.  We offer the greatest inventory of larger specimens available.  These will be available for local sale in Hawaii and listed in our online store section of this website when it reopens in late May 2017.

Warning.  The sap of this and other Adenium species is poisonous.  Keep the plants out of the reach of young children.  Wash your hands thoroughly after any contact with the sap.  Wear eye protection when pruning the plant.

 

Shipping Information

Our Socotra roses can be shipped to all states except Arizona, California, Louisiana and Texas.  The plants will be shipped bare root and must be inspected and released by the Hawaii Department of Agriculture before shipment to the neighbor islands of Hawaii and other states.  The plants should be ordered before the onset of freezing temperatures at their destination.  Socotra roses are sensitive to cold temperatures but are otherwise resilient to normal shipping conditions.  For additional information on shipping please refer to this page.

Plant Care Recommendations

Socotra roses require warm growing conditions and high sunlight levels.  They can be grown outdoors in frost free tropical climates or kept as indoor plants.  For additional information on care of these plants please refer to our instruction sheet.

 

References

[1] Eternal Yemen Tour Operator.  2016.   Poisonous beauty: Adenum obesum socotranum – endemic succulent of Socotra Island, Yemen.  http://eternalyemen.blogspot.com/2014/12/poisonous-beauty-adenum-obesum.html  [accessed 2017 May 02].

[2] Miller, A. 2004. Adenium obesum ssp. sokotranum. The IUCN Red List of Threatened Species 2004: e.T33687A9797051. http://dx.doi.org/10.2305/IUCN.UK.2004.RLTS.T33687A9797051.en.   [accessed 2017 May 4].

[3] Bawazir AA, Bamousa AS.  2014.  Biodiversity and conservation of plant genetic resources on Socotra.  Dis. J. Ag. Food Sci. 2(7):217-224.  http://resjournals.org/JAFS/PDF/2014/Jul/Bawazir_and_Bamousa.pdf   [accessed 2017 May 02].

[4] Kiyohara H, Ichino C, Kawamura Y, Nagai T, Sato N, Yamada H, Salama MM, Abdel-Sattar E.  2012.  In vitro anti-influenza virus activity of a cardiotonic glycoside from Adenium obesum (Forssk.).  Phytomedicine. 19(2):111-4.

[5] Hoffmann JJ, Cole JR.  1977.  Phytochemical investigation of Adenium obesum Forskal (Apocynaceae): isolation and identification of cytotoxic agents.  J Pharm Sci. 66(9):1336-8.

[6] Yamauchi T, Abe F.  1990.  Cardiac glycosides and pregnanes from Adenium obesum (studies on the constituents of Adenium. I).  Chem Pharm Bull (Tokyo). 38(3):669-72.

[7] Arai MA, Tateno C, Koyano T, Kowithayakorn T, Kawabe S, Ishibashi M.  2011.  New hedgehog/GLI-signaling inhibitors from Adenium obesum.  Org Biomol Chem. 9(4):1133-9.

[8] Kiyohara H, Ichino C, Kawamura Y, Nagai T, Sato N, Yamada H, Salama MM, Abdel-Sattar E.  2012.  In vitro anti-influenza virus activity of a cardiotonic glycoside from Adenium obesum (Forssk.).  Phytomedicine. 19(2):111-4.

[9] Almehdar H, Abdallah HM, Osman AM, Abdel-Sattar EA.  2012.  In vitro cytotoxic screening of selected Saudi medicinal plants.  J Nat Med. 66(2):406-12.

[10] Farah MA, Ali MA, Chen SM, Li Y, Al-Hemaid FM, Abou-Tarboush FM, Al-Anazi KM, Lee J.  2016.  Silver nanoparticles synthesized from Adenium obesum leaf extract induced DNA damage, apoptosis and autophagy via generation of reactive oxygen species.  Colloids Surf B Biointerfaces.  141:158-69.

[11] Ahmed SK, Versiani MA, Ikram A, Sattar SA, Faizi S.  2017.  Cytotoxic cardiac glycosides from the fruit (pods) of Adenium obesum (Forssk.) Roem. & Schult.  Nat Prod Res. 201731(10):1205-1208.

[12] Damme KV, Banfield L.  2011.  Past and present human impacts on the biodiversity of Socotra Island (Yemen): implications for future conservation.  Zool. Middle East.  54(3):31-88.

[13]  Lavranos JJ.  2012.  Adenium socotranum.  Cactus and Succulent Journal.  84(3):159-159. 2012
doi: http://dx.doi.org/10.2985/0007-9367-84.3.159