Family Burseraceae

Burseraceae Kunth

Including Balsameaceae Dum.

Habit and leaf form. Trees, or shrubs; bearing essential oils (in the bark); resinous. Leaves alternate; spiral, or distichous (rarely); petiolate; non-sheathing; gland-dotted (rarely), or not gland-dotted; aromatic (resinous, but usually not punctate); compound; pinnate, or ternate, or unifoliolate (rarely); exstipulate (usually), or stipulate (rarely); without a persistent basal meristem. Domatia occurring in the family (in one genus); manifested as pits, or hair tufts.

Leaf anatomy. Mucilaginous epidermis present (commonly), or absent. Stomata present; anomocytic.

Adaxial hypodermis present, or absent. Lamina dorsiventral (usually), or isobilateral; without secretory cavities. The mesophyll containing mucilage cells, or not containing mucilage cells. Minor leaf veins without phloem transfer cells (Commiphora).

Stem anatomy. Secretory cavities present; with resin. Cork cambium present; initially superficial (usually), or deep-seated. Nodes multilacunar. Cortical bundles absent. Medullary bundles present (Canarium), or absent. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with libriform fibres; with vessels. Vessel end-walls simple. Vessels without vestured pits. Wood parenchyma paratracheal.

Reproductive type, pollination. Plants hermaphrodite, or dioecious, or polygamomonoecious.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes, in racemes, and in heads. Inflorescences often in thyrses. Flowers small; regular; 3–5 merous; cyclic; tetracyclic, or pentacyclic. Hypogynous disk present, or absent.

Perianth with distinct calyx and corolla (usually), or sepaline (corolla sometimes lacking); 6–10; normally 2 whorled; isomerous. Calyx (3–)4, or 5; 1 whorled; gamosepalous (the sepals usually basally connate); regular; imbricate, or valvate. Corolla when present, (3–)4, or 5; 1 whorled; polypetalous, or gamopetalous (rarely); imbricate, or valvate; regular.

Androecium 3–5, or 6–10. Androecial members free of the perianth; markedly unequal (often, when two whorls), or all equal; free of one another (usually), or coherent (rarely); when coherent 1 adelphous (via connate filaments); 1 whorled, or 2 whorled. Androecium exclusively of fertile stamens. Stamens 4–5, or 8–10; diplostemonous (usually), or isomerous with the perianth; when one whorled alternisepalous. Anthers dorsifixed (slightly), or basifixed; versatile (slightly), or non-versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate; appendaged, or unappendaged. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads usually tetrahedral. Anther wall initially with one middle layer, or initially with more than one middle layer. Tapetum glandular. Pollen grains aperturate; commonly 3 aperturate; commonly colporate; 2-celled.

Gynoecium (2–)3–5 carpelled. Carpels reduced in number relative to the perianth to isomerous with the perianth. The pistil (2–)3–5 celled. Gynoecium syncarpous; synstylovarious; superior. Ovary (2–)3–5 locular. Styles 1. Placentation axile. Ovules (1–)2 per locule; pendulous; epitropous (micropyle superior); with ventral raphe; non-arillate; hemianatropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked. Endosperm formation nuclear.

Fruit fleshy, or non-fleshy; indehiscent (usually), or dehiscent; a drupe (usually, or drupelike), or a capsule (rarely). The drupes with separable pyrenes, or with one stone. Seeds non-endospermic (or almost so). Cotyledons 2. Embryo chlorophyllous (2/2); straight or rolled.

Seedling. Germination phanerocotylar, or cryptocotylar.

Physiology, biochemistry. Alkaloids present, or absent (mostly). Iridoids not detected. Proanthocyanidins present; cyanidin. Flavonols present; kaempferol and quercetin. Ellagic acid absent (Protium). Saponins/sapogenins present, or absent (rarely). Aluminium accumulation not found. Sugars transported as sucrose (in Bursera). C3.

Geography, cytology. Sub-tropical and tropical. Widespread. X = 11, 13, 23.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rutiflorae; Rutales. Cronquist’s Subclass Rosidae; Sapindales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; malvid; Order Sapindales.

Species 500. Genera 17; Aucoumea, Beiselia, Boswellia, Bursera, Canarium, Commiphora, Crepidospermum, Dacryodes, Garuga, Haplolobus, Pachylobus, Protium, Santiria, Scutinanthe, Tetragastris, Trattinnickia, Triomma.

Illustrations.
• Technical details: Dacryodes: (Thonner).
• Technical details: Bursera, Protium (Lindley).