Socotran Fig Tree (Dorstenia gigas): Extraordinary Forms of a Near Threatened Bottle Tree

Socotran Fig Trees are members of the angiosperm division of flowering plants, because their seeds are covered when pollinated. They are placed in the eudicot clade, because their pollen has three or more pores.

The trees are put in the rosid clade, because of the multiples of 4 or 5 in which their floral parts occur. They are within the order rosales, because of the nitrogen fixing activities of their roots. The macronutrient nitrogen thereby becomes available for food web members and other plant roots in the soil.

The Socotran Fig Tree figures among Moraceae family members, because it has milky sap that is produced by laticifers (Latin: latici-, “liquid” + -ferre, “to bear”), or elongated leaf and stem cells for producing latex and rubber. In fact, the fig and mulberry family is a common name for the Moraceae family of such other laticiferous shrubs and trees as almonds, apples, apricots, banyans, blackberries, breadfruit, elms, hawthorns, nettles, peaches, pears, plums, raspberries, roses, rowan, and strawberries.

Socotran Fig Trees join other Dorstenia genus members in having shield-like flowers and palm tree-like single stems. The genus name in fact memorializes Theodor Dorsten (1492-May 15, 1552), German botanist and physician as well as professor of medicine at the University of Marburg.

The trees occupy the species gigas (Greek: γίγας, “giant”), because they can mature to relatively gigantic heights. In fact, they are the largest members of the genus Dorstenia.

The Socotran Fig Tree is endemic to Socotra, which is an Indian Ocean island about 150 miles (240 kilometers, 130.35 nautical miles) east of the northeast African country of Somalia and 240 miles (380 kilometers; 208.55 nautical miles) south of the southern Arabian peninsular Republic of Yemen, of which it is a part. It is found growing on the island’s center-west region at heights between 1,968.50 and 3,608.92 feet (600 and 1,100 meters) above sea level. It looks as though it has no need for soil since it appears to grow straight out of boulder strewn limestone plateaus and the rocky granite cliffs of the Haggeher Mountains.

During his expedition of 1898 to 1899 to the island, Scottish botanist, explorer and ornithologist Henry Ogg Forbes (January 30, 1851-October 27, 1932) indeed observed Socotran Fig Trees:

“On the limestone hills above our camp at Homhil, growing in crevices of the rocks and assuming extraordinary forms… .” (page 506)

Baltic German botanist, ethnologist and palaeontologist Georg August Schweinfurth (December 29, 1836-September 19, 1925) from Riga, Latvia spent six weeks on Socotra, during April and May 1881. He was accompanied on his expedition by Dr. Emil Riebeck (June 11, 1853-June 22, 1885), German ethnologist, explorer, mineralogist and naturalist from Preusslitz in northeastern Germany. Dr. Schweinfurth wrote a description of the Socotran Fig Tree, which he named in 1883:

". . . With a well-developed, extremely thick, fleshy, branching above ground tree trunk; puckered, oblanceolate leaves; round  receptacle; [receptacle] margin provided with 6-8 bracts."

(". . . caulescens caudice crassissimo carnoso ramoso; foliis oblanceolatis bullatis; receptaculo orbiculari margine 6-8-radiato.") (Balfour, Diagnoses, page 96)

On March 10, 1883, Dr. Schweinfurth sent a postcard from Cairo to (Sir) William Thiselton-Dyer (July 28, 1843-December 23, 1928), then Assistant Director of Royals Gardens, Kew. Dr. Schweinfurth advised that he was sending a case of "living plants" from Socotra, South Nubia, and South Arabia in accordance with the request of Kew's Director, Sir Joseph Dalton Hooker (June 30, 1817-December 10, 1911). As endemic Socotran specimens, Dorstenia gigas was accompanied by Notonia, a genus in the Compositae family (known commonly as asters, daisies or sunflowers) and Jatropha in the Euphorbiaceae family.

Five years later, Scottish botanist Sir Isaac Bayley Balfour (March 31, 1853-November 30, 1922) noted:

"Schweinfurth got splendid flowering specimens . . . There are several plants of this now growing in this country, and Schweinfurth has it in cultivation in Cairo." (page 281)

The Socotran Fig Tree is considered a pachycaul (Greek: παχύς, pachy, “thick” + Latin: cauli, “trunk”) succulent shrub. It matures to a height of 4 to 8 feet (1.2 to  2.4 meters). Its fine roots may require 1-1/2 to 2 times that figure in underground space. Consequently, there needs to be 8 to 16 feet (2.4 to 4.87 meters) of distance between all seedlings as well as between seedlings and structures such as buildings, driveways, fences, paths and walls.

Bark, branches, and trunk:

The tree’s bark becomes pearly or light yellowish white with age. When injured, it exudes a non poisonous sap that is milky in consistency and yellow in color. With age, it is pockmarked attractively with white or pale green scars from leaves that grow and drop.

The many tree branches are gnarled. They grow right out of the sides and top of the trunk. They remain short even though they thicken considerably with age.

The trunk, which generally is called caudex (Latin for “tree stem, tree trunk”), has a swollen base which may measure 12 inches (30.48 centimeters) across at ground level. It looks like a bottle, a bud vase, or, as noted by Henry Ogg Forbes:

". . . Adenium, Dendrosicyos, and Dorstenia, an interesting triad whose swollen stems suggested their being afflicted with elephantiasis." (page xli)

In fact, the tree’s lower diameter may mature to 4 to 6 feet (1.2 to 1.8 meters) at its thickest. It then may taper back to 2 feet (60.96 centimeters) at stem top.

Leaves:

Broad leaves grow directly out from the ends of the branches. They have deeply grooved veins. They look puckered and feel bumpy, corrugated and leathery. They may be quite variable in shape: obovate, with the narrower end at the base; oval, in the shape of an egg; or round. They will be maroon in color if they grow in direct, full, intense sunlight. Otherwise, they will mature from light or yellow green to dark glossy green.

Socotran Fig Trees go dormant throughout the winter. They handle cooler temperatures, between 60 and 69 °F (15.55 and 20.55 °Celsius), during their dormant months. They will drop leaves going into dormancy and produce new leaves or flowers coming out.

Flowers:

Inconspicuous, small green to greenish yellow brown flowers appear when the young tree is at least 5 years old and has a trunk diameter of at least 8 inches (20.32 centimeters). They bloom in March. They grow from a sunflower-like flattened receptacle, which is called a hypanthodium (Greek: ὑπό, hupo, “under” + ἄνθος, anthos, “flower” + Latin -ium, “condition of”) and which is fringed by 6 to 8 fleshy, horn-like bracts. Flower production may occur throughout the growing season, only to suddenly stop before and restart after dormancy.

Even though the Socotran Fig Tree flower is monoecious (Greek: μόνος, monos, “alone, single” + οἰκία, oikia, “house”) in having female and male reproductive parts, it ironically requires the flower of another tree in order to fertilize, pollinate and produce seed.

Fruits:

Socotran Fig Tree fruits are considered drupes, whereby a protective endocarp ("inner fruit") separates the seed from the fleshy mesocarp ("middle fruit"), which in turn is covered by the protective skin of the exocarp ("outer fruit"). They consist of very small stone fruits that are embedded in the flat, fleshy, round receptacle from which the flowers grow. Each fruit contains just one seed. To wildlife it offers bitter bites that nevertheless brim with calcium, fiber, moisture, sugar and vitamins.

Seeds:

The many tiny seeds are covered with minuscule growths. The pods of ripened seeds open spontaneously. The receptacle that houses the tree's flowers and fruits then showers the immediate area with countless numbers of jumping, popping seeds.

Socotran Fig Trees grow on the inaccessible heights of alkaline, calcareous or rocky well-drained ground. They endure high heat and light and low humidity and moisture. But they need not be expected to soldier in cultivation the extreme extremes which they tough out in the wild.

1.Temperatures between 62 and 85° Fahrenheit (16.6 and 31.1° Celsius) during dormancy and between 72 and 94° F (22.2 and 34.4° C) during growth:  In the wild, Socotran Fig Trees may experience dormant weather temperature drops down to 60° F (15.55° Celsius). In cultivation, they may survive rare drops down to 35° F (4.5° C), but they cannot handle freezing temperatures or frozen ground. Generally, this means temperatures between 75 and 85° F (23.8 and 31.1° C) in cultivation.

2. Light 7 to 8 hours daily:  Seedlings and young trees benefit from the indirect light of protected southerly locations outdoors and from reflected light inside. Mature trees handle direct, full, intense light as long as they are not dried out or waterlogged.

3. Moisture evenly distributed throughout the year and equivalent to about 40 inches (1000 millimeters) in irrigation/rainfall:  In cultivation, this generally means year-round supplemental watering every 7 to 10 days unless the roots are dried out and need more or waterlogged and need less.

4. Humidity at 20% during dormancy and at 30 to 40% during growth.

5. Gravelly, gritty soils with pH levels between the mildly acidic 6.0 to the neutral 6.5 or the mildly alkaline above 7.0:  In the wild, Socotran Fig Trees are unaccustomed to fertile, nutrient rich soil. Instead, they grow in calcium, calcium carbonate or limestone rich plateaus or on granite slopes. In cultivation, they will appreciate crushed limestone or decomposed granite, gravel and pumice mixes for root growth on top of any well draining soil.

6. Propagation:  Cuttings and seeding are the two main propagation methods. Softwood cuttings can be taken from the shoot tips of a 2 to 3 year old tree. Cleaned with tap water and liquid detergent and then rinsed with sterile water, they may root in no more than 3 weeks. They should flower and seed in 5 to 7 years.

Seeds then can supplement cuttings in building a collection of bonsai, house, porch and even yard plants depending upon the climate in question.

Fodder, medicine and ornamental ecology are the main traditional and modern uses of Socotran Fig Trees. Specifically, trees can be felled for their swollen, water-filled bases to be processed into pulp and served as drought fodder for goats. Extracts can be used to treat skin diseases. Additionally, research by scientists H. Bakthir, N.A. Awadh Ali, N. Arnold, A. Teichert and L. Wessjohann indicates that extracts also may have modern potential, such as in the treatment of Alzheimer's disease, because of the blocking effects of the furanocoumarins, or plant toxins, in the tree's leaves and twigs upon acetylcholinesterase, an enzyme in the small intestine.

Throughout Socotra’s history, and even today, Socotran Fig Trees are one of many plant species which add both ornamental and utilitarian value to the landscape. For example, they build soil texture through the air and water pore spaces that their roots create below ground. They decrease the atmospheric content of carbon dioxide and increase oxygen levels through respiration. They store readily accessible water in their trunks against the all too frequent times of drought. Additionally, as conservationists, cultivators and researchers increasingly realize, Socotran Fig Trees support scientific advancement through their successful adaptation to extreme environments.

The International Union for Conservation of Nature and Natural Resources regularly compiles and publishes the IUCN Red List of Threatened Species. IUCN team specialists gave the Socotran Fig Tree the conservation status of vulnerable to extinction in 1978, 1997 and 1998. But the assessment in 2004 by Anthony G. Miller (born 1951), Edinburgh Royal Botanic Garden botanist and Arabian Peninsula plant specialist, resulted in the tree’s promotion to the bit less worrisome category of near threatened.

The status upgrade can be seen as the efficacy of organized, sustained action in the face of the environmental challenges of changing climate conditions as well as habitat loss and destruction. Specifically, Socotran Fig Trees grow over a much reduced area of their insular homeland. The situation reflects the historic mortality of trees through the atmospheric and terrestrial drying trends which impact resource availability and use on the tropical semi-desert island of Socotra.

Many responses in fact encourage cultivation of Socotran Fig Trees and thereby protect those in the wild. For example, one initiative is the Socotra Botanic Garden and Nursery for Endemic Plants, which benefits from a longstanding interaction with the Scottish Rock Garden Club dating back to the appointment of Sir Isaac Bayley Balfour FRS FRSE (March 31, 1853-November 30, 1922) as RGBE Regius Keeper. A second initiative promotes the controlled sale of tissue culture raised Socotran Fig Trees through the Socotra Conservation and Development Programme to European horticultural firms that then will channel 10% of gross revenue into conservation on Socotra. A third initiative relates to controlled collection and import of animals and plants on Socotra through the Yemeni Environment Protection Agency.

What it all means is growing recognition as a household name and increased commitment to survival for extraordinarily formed, near threatened Socotran Fig Trees in the wilds of Socotra as well as in cultivation at home and abroad.

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Egyptian vulture (Neophron percnopterus): HopeHill, CC BY 2.0, via Flickr @ https://www.flickr.com/photos/45340412@N06/4438646907/

Dorstenia radiata: Mike Keeling (graftedno1), CC BY-ND 2.0, via Flickr @ https://www.flickr.com/photos/pachytime/1501326560/

sea port of Al Mukalla, Yemen, as seen from Indian Ocean: TastyCakes, Public Domain, via Wikimedia Commons @ https://en.wikipedia.org/wiki/File:Makulla_from_Hadramaut.jpg

undated portrait of Georg Schweinfurth: H.F. Helmolt-History (1903), Vol III, pages 494-495, Public Domain, via Internet Archive @ https://archive.org/details/cu31924088477959/page/n579/mode/1up?view=theater

drawing by Georg August Schweinfurth: A. Engler-Monographieen (1898), Vol I, Figure 2, page 9, Public Domain, via Internet Archive @ https://archive.org/details/monographieenafr01engl/page/9/mode/1up?view=theater

closeup, Dorstenia gigas leaves: Stan Shebs, CC BY-SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Dorstenia_gigas_2.jpg

closeup of Dorstenia gigas flower, propagated in University of California Botanical Garden, Berkeley: Stan Shebs, CC BY-SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Dorstenia_gigas_3.jpg

Desert Rose (Adenium obesum): HopeHill, CC BY 2.0, via Flickr @ https://www.flickr.com/photos/45340412@N06/4452267603/

Dorstenia gigas, propagated in University of California Botanical Garden, Berkeley: Daderot, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Dorstenia_gigas_-_University_of_California_Botanical_Garden_-_DSC08837.JPG

Naturalist Richard Lydekker (1849-1915) noted Abyssinian walia's liquid whistle, penchant for fruits, especially figs: Richard Lydekker-Royal Natural History (1895), Vol IV, page 365, Public Domain, via Internet Archive @ https://archive.org/details/royalnaturalhist04lyderich/page/365/mode/1up?view=theater

Figure 1D, cross-section of Dorstenia gigas trunk in A. Engler-Monographieen (1898), Vol I, Figure 2, page 9, Public Domain, via Internet Archive: https://archive.org/details/monographieenafr01engl/page/8/mode/1up?view=theater

Dorstenia gigas, Sukkulenten-Sammlung (Succulent Plant Collection), Zurich, north central Switzerland: James Steakley, CC BY SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Dorstenia_gigas_(Sukkulentensammlung).jpg

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