Burseraceae

The Burseraceae trees or shrubs are characterized by resins (having triterpenoids and ethereal oils) that are present within the plant tissue from the vertical resin canals and ducts in the bark to the leaf veins. In fact, the synapomorphy of the Burseraceae is the smooth yet peeling or flaking aromatic bark. The clear, nonallergenic resins may smell like almonds, but at least the most well known resins, frankincense and myrrh, have a distinct odor. The leaves are generally alternate, spiral, and odd-pinnately compound with opposite, frequently long-petiolulate, entire to serrate, pinnately veined leaflets whose symmetry is distinctive in some genera. However, some members are known to have trifoliate or unifoliate leaves. The leaf and leaflet stalks and axis may be brown and scurfy, while the leaf base is swollen and may be concave adaxially. The family members tend to be without stipules. The determinate, axillary inflorescences carry small, radial, unisexual flowers. The plants tend to be dioecious. The flowers may have four or five faintly connate but imbricate sepals with an equal number of distinct, imbricate petals. Also, the stamens, that may contain nectar discs, have distinct glabrous filaments that occur in one or two whorls and in numbers equaling or twice the number of petals; the tricolporate pollen is contained within two locules of the anthers that open longitudinally along slits. The gynoecium contains 3–5 connate carpels, one style, and one stigma that is head-like to lobed. Each locule of the superior ovary has two ovules with axile placentation that are anatropous to campylotropous. The one- to five-pitted fruit is a drupe that opens at maturity. The endosperm is usually lacking in the embryo. ==Taxonomy==

Some discrepancy exists in the literature about the size of the Burseraceae. Records say that the family has 17 According to a pollen studies and molecular data, the family is split into three tribes: the Protieae, Bursereae, and Canarieae. The Protieae are composed of Protium (147 species and largest in this tribe), Crepidospermum, Garuga, and Tetragastris. • Aucoumea • Beiselia • Boswellia (frankincense) • Bursera (Palo Santo) • Commiphora (myrrh) • Garuga • Triomma ;Canarieae • Ambilobea • Canarium • Dacryodes • Haplolobus • Pseudodacryodes • Rosselia • Santiria • Scutinanthe • Trattinnickia ;Protieae • Protium (including Tetragastris) (copal) ;Unplaced • †Barghoornia (Ypresian Klondike Mountain Formation) • Pachylobus ==Order==

According to the literature, the Burseraceae have not been lumped with other families nor split up into several others. However, they have "jumped" orders several times. For example, in the early 19th century, the family seems to have been placed in the Burserales, with the Anacardiaceae and Podoaceae. In the mid-19th century and early 20th century, the family was placed in the Geraniales. 460 genera, However, the two families have several distinguishing characteristics. The resin of the Burseraceae is nonallergenic and two ovules per carpel occur, whereas the resin of the Anacardiaceae can be allergenic or poisonous and one ovule per carpel is found. The Burseraceae-Anacardiaceae clade is sister to a robust cluster of three other families, the Sapindaceae-Aceraceae-Hippocastanaceae clade. The Rutaceae-Meliaceae-Simaroubaceae clade is sister to the Burseraceae-Anacardiaceae and Sapindaceae-Aceraceae-Hippocastanaceae clade. The rbcL technique is supported and considered acceptable until such time as other analytical methods become better developed. ==Biogeography==

The Burseraceae are distributed throughout the world and primarily in the tropics, especially Malesia, Africa, and Central and South America. find that Beiselia mexicana, a native of Mexico, is basal to the remaining Burseraceae. These results may indicate that the family originated in Mexico. The next divergence was in the Early Eocene when the Burserinae (i.e. Commiphora) diverged and emigrated from North America into Africa, Madagascar, and India. Commiphora dispersed throughout Africa during the Middle Eocene (about 44 Mya) and from Africa to Madagascar during the Oligocene (about 30 Mya) via the Mozambique Channel Land Bridge; the spread to India was more recent (about 5 Mya). The Canarieae and Boswelliinae (subtribes of Bursereae) dispersed from western Laurasia and spread eastward during the Eocene; fossils of Canarium, for example, from the Czech Republic date to the Late Oligocene (23 Mya). Finally, the Protieae originated in North America like the rest of the family, then migrated to Africa and Asia through the Tethys seaway in the Late Eocene (about 37 Mya), but then made its way back to South America via long-distance dispersal. By the late Oligocene (about 23Mya), all three Burseraceae tribes were extant and dispersed throughout the Northern Hemisphere. The mechanism of seed dispersal via animal link vectors (endozoochoric dispersal) may explain how most Burseraceae were able to expand their range so efficiently across the globe. Beiselia, Boswellia, and Triomma have dry fruits better suited for wind dispersal, but most Burseraceae have fleshy, edible fruit that is eaten by many animal dispersers. The seeds may provide a high reward in fat (24–73%) and protein (2.7–25.9%) if digested, but many animals eat just the fleshy part of the fruit and either discard the endocarp right away or excrete it some time later. Some known Burseraceae fruit consumers include hornbills (Buceros bicornis, Ceratogyma atrata, C. cylindricus, Penelopides panini), oilbirds (Steatnoris caripensis), fruit pigeons, warblers, vireos, orioles, flycatchers, tanagers, woodpeckers, loeries, primates (Cercopithecus spp., Lophocebus albigena), lemurs (Varecia variegate subsp. variegate), and sun bears (Helarctos malayanus). The fruits may also have been water dispersed. ==Economic significance and ethnobotanic uses==

Several representative species within the Burseraceae typify the economic and ethnobotanic significance of the family. First, Dacryodes excelsa of the Canarieae is an important old-growth species found in the Caribbean. Second, Bursera simaruba of the Burserinae is a fast-growing ornamental that is one of a few representatives of the primarily tropical family in the United States. Finally, the namesakes of the family Boswellia carterii (frankincense) and Commiphora abyssinica (myrrh) are important economically and medicinally in several parts of the world. Though this is a small subset of the large number of potentially important species, these four members exemplify the wide use and importance of the Burseraceae. The latter three are frequently cited in the literature for their renowned importance. Commonly known as tabonuco (or gommier, also candlewood), Dacryodes excelsa is a large, dominant tree found in Puerto Rico and other parts of the Caribbean. The seeds of the tree are a source of food for birds. Like all members, the tree releases sap from the bark when wounded. The clear sap oozes from the tree and hardens to a white, aromatic waxy resin that can be used to make candles and incense. The resin from this tree can be used to make varnish and turpentine. The bark serves as an antidote to skin irritation caused by Metopium toxiferum (also known as poisonwood, Florida poison tree, and hog gum) of the Anacardiaceae. The gumbo limbo grows quickly and can be used to make a living fence especially out of cut limbs that are placed straight into the ground or for restoration projects as a pioneer species. Both species are native to parts of Northeast Africa (Somalia, frankincense; Somalia and Ethiopia, myrrh) and Arabia (Oman and Yemen, frankincense), but their distribution and use have been extended beyond these regions to India and China. At that time, myrrh was worth more than gold. In modern times resins from these trees are used in Chinese herbal medicine and Indian Ayurvedic medicine to treat several ailments. Pills containing small doses of frankincense and other ingredients are valued in oriental medicine for promoting blood flow and the movement of the qi (‘life force’ or ‘spiritual energy’). and myrrh are used to relieve pain and inflammation as in arthritis and asthma. ==References==