Friday, March 1, 2019

[Botany • 2019] Boswellia occulta (Burseraceae) • A New Species of Frankincense Tree from Somalia (Somaliland)

Boswellia occulta Thulin, DeCarlo & S.P.Johnson

in Thulin, DeCarlo & Johnson, 2019.

The new species Boswellia occulta is described from a small area in the Ceel Afweyn District of Somaliland (northwestern Somalia), where it is locally of considerable socio-economic importance. Although used for frankincense production by many generations of local harvesters, it has been unknown to science until now. Apart from the recently collected type material, it is also known from a sterile and hitherto misunderstood collection made in 1945. The simple-leaved Boswellia occulta is morphologically compared with B. sacra and B. frereana, the two major frankincense-producing species in the region, both with imparipinnate leaves, and it appears to be most closely related to B. sacra. The new species is the only simple-leaved species of Boswellia known outside Socotra.

Keywords: Boswellia, frankincense, taxonomy, Somaliland, Eudicots

FIGURE 1. Holotype of Boswellia occulta, with field label and still unmounted.
 Photograph: Stephen P. Johnson.

FIGURE 2. Boswellia occulta, from the type locality
A. Tree, in leaf; B. Tree, showing swollen disk-shaped base when growing on rock; C. Branches, showing foliage; D. Trunk with incisions, showing resin oozing out.
Photographs: Ahmed Mohamed Dhunkaal.

Boswellia occulta Thulin, DeCarlo & S.P.Johnson sp. nov.

Boswellia occulta differs from B. frereana by its flowers with white (vs reddish or greenish red) petals and tubular (vs flattened) disk, and fruits with 4–5 [vs (5–)6(–8)] locules; and from B. sacra by its glabrous (vs ± densely pubescent) leaves with mostly strongly undulate-sinuate (vs crenate to subentire) margins, and unwinged pyrenes (vs pyrenes often more or less surrounded by a persistent wing); and from both B. frereana and B. sacra by its simple (vs imparipinnate) leaves.

Distribution and habitat:— Boswellia occulta is only known from a small area in northwestern Somalia (Somaliland) (Fig. 4), where it is locally common and the dominant tree on west-facing arid hillsides on limestone at 400–500 m elevation. The tree usually grows directly on limestone cliffs and boulders, and then has a more or less swollen disk-shaped base of the trunk (Fig. 2B). More detailed studies of the extent of the range of the species and the numbers and densities of the trees and their regeneration are planned in the near future.

Etymology:— The epithet “occulta” (from Latin “occultus”, hidden) refers to the history of this species that, although used for frankincense production by many generations of local harvesters, has been unknown to science until now.

Vernacular name and uses:— Mohor madow (Somali, fide Glover & Gilliland 719 and Ahmed Mohamed Dhunkaal s.n.); this is the vernacular name generally used also for B. sacra in Somalia. However, the harvesters in the B. occulta area distinguish between B. occulta (“mohor madow”) and B. sacra (“mohor cad”, “mohor dadbeed” or “mohor lab”). Frankincense produced from B. occulta (Fig. 2D) has unique properties (DeCarlo, unpublished research data) and is important in the local economy

Mats Thulin, Anjanette DeCarlo and Stephen P. Johnson. 2019. Boswellia occulta (Burseraceae), A New Species of Frankincense Tree from Somalia (Somaliland). Phytotaxa. 394(3); 219–224.   DOI: 10.11646/phytotaxa.394.3.3