Socotra Frankincense Tree (Boswellia socotrana): Island of the Phoenix and Its Vulnerable Incense

The Socotran Frankincense Tree is a member of the angiosperm division of flowering plants whose seeds are enclosed when they are pollinated. It is found in the eudicot clade, which is characterized by pollen with three or more pores. It is grouped into the rosid clade, whose members tend to have flower parts in multiples of 4 or 5. It is in the sapindale order, which is populated mainly by trees and large shrubs whose many leaflets form into compound leaves. It is placed in the Burseraceae family, which is known for flaking or peeling bark, nonallergic resin, pitted drupe fruits, and swollen leaf bases. It is put in the genus Boswellia, the bark of whose members produces fragrant resins which traditionally are used as incense and in medical treatments of inflammation and pain. It is within the species socotrana, which means "of or relating to Socotra."

Each species distinguishes itself through habitat or even foliage or floral details. For example, in his assessment of amaro's status for the International Union for Conservation of Nature's Red List of Threatened Species, Anthony G. Miller (born 1951) of the Royal Botanic Garden Edinburgh noted:

"A hill side of trees of B. ameero in full flowers is one of the most dramatic sights on the island."

Boswellia elongata favors altitudes of 2,296.5 to 2,624.6 feet (700 to 800 meters) on limestone cliffs, has large flowers, and its gum-resin is "not so penetratingly fragrant" as Boswellia ameero (Balfour, p. 50).

Sir Isaac Bayley Balfour FRS FRSE (March 31, 1853-November 30, 1922) is the first known European to discover the Socotran Frankincense Tree. The Scottish botanist made his discovery during a 48-day arboreal and botanical expedition to Socotra. Frankincense trees were still plenteous then. Sir Balfour noted:

". . . Boswellia . . . are represented in Socotra, and there probably more copiously than in any other area of like extent." (p. 49)

Despite his main interest in the plants of China and the Himalayan Mountain countries, the Edinburgh native found time to pursue investigations into the animal and plant life of such isolated Indian Ocean islands as Rodrigues in 1874 and Socotra in 1880.

The Socotran Frankincense Tree can be quite variable in its look. For example, it may be found growing as a vertically spreading shrub on upland plateaus. Or it may take the shape of a tree on rocky mountain slopes where, according to former U.S. Consul General to Aden, Arabia Charles Krath Moser (born August 27, 1877):

"We were in the presence of what was undoubtedly a tree, but it looked nearly as much like an enormous sea-serpent in the act of shedding its skin, so awkwardly contorted and alive it seemed."(p. 274)

Bark, branches and trunk

The flaking, peeling bark nevertheless begins life as reddish brown in color and mellows to grey with age. According to English explorer, producer and writer Douglas Botting (born February 22, 1934), it ends up quite scarred from being scraped to be made into buckets and slashed so that “…the clear yellowish-white resin oozes from incisions with a strong aroma.” (p. 160)

The trunk forks low in its tree-like form. In fact, it often looks like two trees growing out of one tree stump. Stiff branches may begin quite low on the woody plant's shrubby variety or more than half way up the trunk on its tree-like variety. As a tree, the trunk may measure just under 12 inches (30.48 centimeters) in diameter and mature to a height of 25 feet (7.62 meters).

Leaves

The dark evergreen, glossy leaves actually are made up of many miniature paddle-like leaflets on winged stalks. Charles Moser compares them to sumac (Rhus spp) leaves whereas Douglas Botting describes them as “…scanty, curly and indented.” (p. 160)

The leaflets grow in pairs on opposite sides of a foliar axis. The particular compound growth arrangement is called imparipinnate (Latin: impari, "odd, unequal, uneven" + pinnātus, "feathered"). The foliar line-up therefore produces an odd number of leaflets such that just one leaflet grows at the end of each set of compound leaves.

Flowers

Charles Moser and Douglas Botting describe the flowers as borne on the ends of short spikes, few in number, geranium-like in shape, and red in color. About four decades later, Anthony Miller finds the variable Socotran Frankincense Tree’s flowers to form into just a few short pale yellow floral clusters.

Each flower has five variable petals, which may be either oblong, whereby length is greater than width, or ovate, whereby the shape is egg-like.

Fruits

Douglas Botting describes the fruit as the shape and size of a marble. The fruit is considered a drupe, whose single seed is separated by the protective endocarp ("inner fruit") from the fleshy mesocarp ("middle fruit") and the tough, outer exocarp ("outside fruit").

Seeds

Socotran Frankincense Trees produce seeds, many of which do not germinate. Germinating seeds produce seedlings that do not survive past a few years. The lack of regeneration suggests habitat degradation, particularly from extended drought.

Socotran Frankincense Trees are accustomed to high heat, intense light and low humidity and moisture in their native habitats. But what they are familiar with in the wild does not have to be carried out to the letter in cultivation. In fact, they particularly will appreciate not having to experience extended, extreme drought as long as they do not end up the waterlogged victim of fungal root rot.

1. Temperatures above freezing: In its native habitat, it deals with a yearly average temperature range between 60 and 90+ °Fahrenheit (15.55 and 32.22°Celsius). In cultivation, that means no freezing temperatures or frozen ground.

2. Light for 7 to 8 hours each day:  On Socotra, the trees are tolerant of direct, intense sunlight when mature. But as germinating seeds and young seedlings, they favor light whose intensity is mitigated by low lying cloud cover, protective shade from surrounding shrubby, succulent and woody plant life, and the shadows cast by landforms, such as boulders.

In cultivation, that means reflected light for a houseplant and a protected southerly location outdoors.

3. Moisture sufficient to keep subsurface ground slightly moist:  On its native island, the tree benefits from approximate average yearly rainfalls of 10 to 40 inches (254 to 1,000 millimeters) on limestone plateaus and rocky slopes, respectively.

In cultivation, that means ground that neither dries out nor waterlogs from the surface about 6 inches (15.24 centimeters) down.

4. Humidity:  Socotran Frankincense Trees are accustomed to dry atmospheric and terrestrial conditions. They are used to monthly average atmospheric moisture levels of 10 to 20% in February and March, June through August, and November and December; 21 to 30% in January, April and September; and 35 to 40% in May and October.

In cultivation, that means dry ambient conditions that encourage controlled evaporation and transpiration but protect against fiercely drying breezes and winds.

5. Soils:  In its native habitat, the Socotran Frankincense Tree grows in a shallow layer of alkaline soil. The soil may have the gravelly look of the eroded, weathered particles that form on the island’s granite mountain slopes. Or it may have the calcium, calcium carbonate or limestone rich consistency of Socotra's inland plateaus.

In cultivation, that means a gravelly, gritty, well draining mix that has a pH above the 6.0 to 7.0 slightly acidic to neutral soil range within which many houseplants and ornamentals thrive. That also means no heavy applications of NPK (nitrogen, phosphorus, potassium) fertilizers.

6. Propagation:  Cuttings and seeding are possible means of propagation. On Socotra, propagation is by natural seed drop to the ground or by wind dispersion. Islanders lack compelling reasons to cultivate the tree since they no longer participate in the world incense trade.

In cultivation, seeds are planted close to the surface, no more than 1/4 inch (0.635 centimeters) down in a crushed limestone or granite layer on top of well draining soil. The growing pots are placed in filtered or reflected light. They are watered in the early morning sufficient to slightly moisten pot contents. They should germinate in 21 days.

The main modern and traditional use of the Socotran Frankincense Tree relates to the woody plant’s resin. Specifically, the resin can be extracted once a month between June and September for processing into air/room/textile fresheners, essential oils, natural insecticides, and ritual incense as well as traditional medicine for inflamed, painful joints.

For example, scientists Ramzi A. Mothana, Ulrike Lindequist, Renate Gruenert and Patrick J. Bednarski analyzed the materials that were extracted with methanol and then hot water from 26 plants collected on Socotra. The researchers found that Socotran Frankincense Tree extracts block cancer cell growth. They also observed that the tree extract’s boswellic acids, essential oils and terpenoids exhibit promising potential in anticancer, antifungal, antimicrobial and antioxidative activities.

Additionally, islanders recycle the bark around resin exit points into buckets and nearby twigs into aromatic, sack encased pillows. They use the dead wood in firing pottery and the resulting ashes as a natural fertilizer.

Socotran Frankincense Trees can be considered living testaments to the ancient glories of the Incense Route. In fact, frankincense is a prized item which represents a successful transition from ancient arrangements of barter and trade to modern exchanges of national currencies and profitable commodities. But it no longer relies upon the Socotran Frankincense Tree for its resinous origins.

Instead, the products of the Socotran Frankincense Tree now fill restricted roles of limited local use. Such roles mirror the steadily plodding consequences of Socotra's historically difficult access as well as changing climate conditions, drying atmospheric and terrestrial trends, and shifting cultural priorities. Such cultural, geographic and meteorological contexts render the endemic Socotran Frankincense Tree vulnerable to the very extinction against which the International Union for Conservation of Nature and Natural Resources warns through its inclusion of the fragrant tree on the IUCN Red List of Threatened Species.

At the same time, the Socotran Frankincense Tree nevertheless responds well to cultivation outside Socotra. The practical applicability, subtle fragrance and unique beauty of its body parts unite to earn for the Socotran Frankincense Tree a devoted following and permanent place among collectors and cultivators of unusual plants for extraordinary but practical ornamentation of interiors and landscapes. It will take the equally committed, concerted efforts of conservationists and scientists to preserve the wild Socotran Frankincense Tree whose stubborn though resilient ancient genetics will not allow it to back down from this latest survivalist fight to the finish on the woody plant's own home grounds on Socotra, an isolated tiny speck in the northwest Indian Ocean and an environmentally unique United Nations Educational Scientific and Cultural Organization (UNESCO) World Heritage Site.

Mythically, a saving grace inheres in the Socotran Frankincense Tree's legendary linkage to the fabled Incense Route. The early marine routes, which preceded the overland route and by which incense was traded to the ancient Egyptians over 3,500 years ago, were organized and navigated by the mysterious Phoenicians, who were unequalled anciently in their enthusiastic, skillful, and undaunted seafaring. In their careful mythology, Phoenicians believed that the nest of the phoenix, the colorfully plumed mythical bird which rises from its own ashes, was made from frankincense and myrrh (Commiphora spp) trees and was located on the highest peak of Socotra's Haggeher Mountains. As one of the chosen trees for this powerful affirmation of life's continuity, the Socotran Frankincense Tree conceivably possesses in its cellular structure an innate fortitude to overcome adversity and rise figuratively from its own ashes.

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

Socotra's frankincense branches: Gerry and Bonni, CC BY 2.0, via Flickr @ https://www.flickr.com/photos/gerr-bon/6408183409/

Boswellia ameero, another of Socotra's endemic frankincense trees: H.O. Forbes-Natural History (1903), p. 461, Public Domain, via Biodiversity Heritage Library @ https://www.biodiversitylibrary.org/page/24884726

Socotran Archipelago in Arabian Sea sector of Indian Ocean: Central Intelligence Agency, Public Domain, via Wikimedia Commons @ http://en.wikipedia.org/wiki/File:Somali_map.jpg

Boswellia ameero: Isaac Bayley Balfour-"Botany" (1888), Tab. IX, Public Domain, via Biodiversity Heritage Library @ http://biodiversitylibrary.org/page/41401512

Socotra's camels are fond of frankincense tree's branches, leaves, and twigs: Gerry and Bonni, CC BY 2.0, via Flickr @ https://www.flickr.com/photos/gerr-bon/6408239431/

Boswellia elongata: Isaac Bayley Balfour-"Botany" (1888), Tab. X, Public Domain, via Internet Archive @ https://archive.org/details/transactionsofro311888roy/page/n570/mode/1up?view=theater

Socotra: Isaac Bayley Balfour-"Botany" (1888), frontispiece, Public Domain, via Biodiversity Heritage Library@ https://www.biodiversitylibrary.org/page/41400959

Socotra frankincense flowers and fruit: Isaac Bayley Balfour-"Botany" (1888), Tab. XI, Public Domain, via Biodiversity Heritage Library @ https://www.biodiversitylibrary.org/page/41401520

1899 photo by Captain H.E. Rosengreen: Richard von Wettstein-Sokótra 1905, p30, Public Domain, via Internet Archive @ https://archive.org/details/Soktra1905/page/n21/mode/2up?view=theater

Socotra frankincense tree (left, foreground) with Adenium (center): HO Forbes-Natural History (1903), p. xli, Public Domain, via Biodiversity Heritage Library @ https://www.biodiversitylibrary.org/page/24884197

Scops socotranus: engraving by Bale & Danielsson, Ltd. after an original by Henrik Grönvold (1858–1940): HO Forbes-Natural History (1903), Plate V (p69), Public Domain, via Biodiversity Heritage Library @ https://www.biodiversitylibrary.org/page/24884298

Phoenix rising from its fiery ashes: Aberdeen Bestiary illuminated manuscript, ca. 12th century, Public Domain, via Wikimedia Commons @ https://en.wikipedia.org/wiki/File:Phoenix_detail_from_Aberdeen_Bestiary.jpg

Phoenix, risen from its ashes, between two trees, frankincense and myrrh: Aberdeen Bestiary, Public Domain, via Wikimedia Commons @ https://en.wikipedia.org/wiki/File:Phoenix_rising_from_its_ashes.jpg

illustration/lithograph by John Green: HO Forbes-Natural History (1903), Plate VIII (p99), Public Domain, via Internet Archive @ https://archive.org/details/naturalhistoryof00forb/page/99/mode/1up?view=theater

Socotra's aloe: Gerry and Bonni, CC BY 2.0, via Flickr @ https://www.flickr.com/photos/gerr-bon/6407177435/

Yemeni riches: frankincense, gold, oil: snotch, Public Domain, via Wikimedia Commons @ https://en.wikipedia.org/wiki/File:Frankincense_2005-12-31.jpg

Balfour, Isaac Bayley. “Botany of Socotra.” Transactions of the Royal Society of Edinburgh: Earth Sciences, Volume XXXI (31). Edinburgh: Robert Grant & Son; London: Williams & Norgate, MDCCCLXXXVIII (1888).

• Available at via Biodiversity Heritage Library at: http://biodiversitylibrary.org/item/129313#page/7/mode/1up
• Available via Internet Archive at:  http://archive.org/details/transactionsofro311888roy

Balfour, Isaac Bayley. Botany of Socotra. Forming Vol. XXXI of The Transactions of the Royal Society of Edinburgh. Edinburgh: Robert Grant & Son; London: Williams & Norgate, MDCCCLXXXVIII (1888).

• Available via Biodiversity Heritage Library at:  http://www.biodiversitylibrary.org/item/42457.
• Available viaInternet Archive at:  http://archive.org/details/botanyofsocotra00balf.

Botting, Douglas. Island of the Dragon’s Blood. London: Hodder and Stoughton, 1958.

Cheung, Catherine, and Lyndon DeVantier. Socotra: A Natural History of the Islands and Their People. Hong Kong: Odyssey Books & Guides, 2006.

Forbes, Henry O., ed. The Natural History of Sokotra and Abd-el-Kuri: Being the Report upon the Results of the Conjoint Expedition to these Islands in 1898-9, by Mr. W.R. Ogilvie-Grant, of the British Museum, and Dr. H.O. Forbes, of the Liverpool Museums, together with information from other available sources Forming A Monograph of the Islands. Liverpool-London: The Free Public Museums, 1903.

• Available via Biodiversity Heritage Library at:  http://biodiversitylibrary.org/item/80063
• Available via Internet Archive at:  http://archive.org/details/naturalhistoryof00forb

Guébourg, Jean-Louis. Socotra, une île hors du temps. Collection îles et archipels, No. 25. Bordeaux: Presses Universitaires de Bordeaux, 1998.

Miller, Anthony G. (2004). "Boswellia ameero." In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.1.

Miller, Anthony G. (2004). "Boswellia socotrana." In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.1.

Moser, Charles K. "The isle of frankincense." National Geographic Magazine, Volume 33 (March 1918): 267-278.

Mothana, Ramzi A., Ulrike Lindequist, Renate Gruenert and Patrick J. Bednarski. "Studies of the in vitro anticancer, antimicrobial and antioxidant potentials of selected Yemeni medicinal plants from the island Soqotra." BMC Complementary and Alternative Medicine, Vol. 9, No. 7 (25 March 2009).

• Available via NCBI (National Center for Biotechnology Information) at:  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2667473/

Ravenstein, Ernest George. "The Island of Socotra." The Geographical Magazine, Volume III (1876): 119-124.

• Available via HathiTrust at: http://catalog.hathitrust.org/Record/000057985

Thulin, Mats. "Two new species of frankincense trees (Boswellia, Burseraceae) from Socotra." Kew Bulletin, Vol. 56, No. 4 (2001): 983-988.

• Available at:  http://www.jstor.org/stable/4119310

Wellsted, J.R. "Memoir on the Island of Socotra." Journal of the Royal Geographical Society of London, Volume 5 (1835): 129-229.

Wettstein, Richard von. "Sokótra 1905." Pictorial work of Plates 25-30, Issue of Georg Karsten and Heinrich Schenck, eds., Vegetationsbilder, Vol. 3, No. 5. Munich: Collotype by A-G Bruckmann; Jena: Gustav Fischer.

• Available via Internet Archive at: http://archive.org/details/Soktra1905