Habit and leaf form. Trees, or shrubs; evergreen, or deciduous; bearing essential oils. Mesophytic, or xerophytic. Leaves opposite, or whorled; leathery, or ‘herbaceous’; petiolate; gland-dotted; aromatic; simple, or compound; unifoliolate, or pinnate. Leaflets 1, or 3. Leaf blades when simple dissected, or entire; when simple/dissected pinnatifid, or much-divided; pinnately veined, or one-veined. Leaves without stipules, or with stipules. Stipules when present, intrapetiolar; represented by glands. Leaf blade margins entire, or crenate. Leaves without a persistent basal meristem. Stem anatomy. Nodes unilacunar, or tri-lacunar. Secondary thickening developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite, or functionally male (the non-functional gynoecium merely a reduced replica of the functional gynoecium), or functionally female. Unisexual flowers present (by abortion (genus does not exhibit strong sexual dimorphism)), or absent. Plants hermaphrodite, or monoecious, or andromonoecious, or polygamomonoecious. Entomophilous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’, or solitary (rarely). Inflorescence few-flowered, or many-flowered. Flowers in cymes, or in panicles. The terminal inflorescence unit cymose, or racemose. Inflorescences terminal (rarely), or axillary; either a 3-flowered, axillary cyme or a branched, many-flowered panicle. Flowers bracteate; small to medium-sized; fragrant; regular, or somewhat irregular. The floral asymmetry when noticeable, involving the perianth and involving the androecium (not K). Flowers 4 merous; cyclic. Floral receptacle developing a gynophore (associated with the disk), or with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk present (4–8-lobed or entire); intrastaminal; annular (sometimes one-sided), or of separate members. Perianth with distinct calyx and corolla; 8; 2 -whorled; isomerous. Calyx 4; 1 -whorled; polysepalous; imbricate; regular; persistent, or not persistent; with the median member posterior. Corolla 4; 1 -whorled; polypetalous, or gamopetalous; imbricate, or valvate; regular, or unequal but not bilabiate. Fertile stamens present, or absent (from female flowers). Androecium 4, or 8. Androecial members unbranched, or branched (? by the splitting of simple primordia); free of the perianth; markedly unequal (of 2 lengths); free of one another, or coherent (? the filaments usually more or less basally connate); 1 - adelphous, or 3–12 - adelphous; 1 -whorled, or 2 -whorled. Stamens 4, or 8, or 4–8 (rarely); isomerous with the perianth, or diplostemonous; alternisepalous, or oppositisepalous (? when the outer whorl lost); filantherous. Anthers dorsifixed, or basifixed (? more or less); versatile; dehiscing via longitudinal slits; introrse, or latrorse; tetrasporangiate. Fertile gynoecium present, or absent (from male flowers). Gynoecium 4 carpelled. The pistil 4 celled. Gynoecium syncarpous; semicarpous, or synovarious, or synstylovarious, or eu-syncarpous, or synstylous; superior. Ovary plurilocular; 4 locular. Gynoecium stylate. Styles 4; partially joined (united from base upwards or at tip only); apical (or subterminal). Stigmas 1 - lobed, or 4 - lobed; capitate, or peltate; wet type, or dry type; papillate, or non-papillate; Group II type, or Group IV type. Placentation axile. Ovules 1 per locule, or 2 per locule; pendulous to ascending; epitropous; collateral; arillate, or non-arillate; anatropous, or hemianatropous.
Fruit and seed features. Fruit fleshy, or non-fleshy; an aggregate, or not an aggregate. The fruiting carpels coalescing into a secondary syncarp, or not coalescing. The fruiting carpel dehiscent, or indehiscent; a follicle (erect to spreading, 1–2-seeded). Fruit dehiscent, or indehiscent; when eu-syncarpous a capsule. Seeds endospermic, or non-endospermic. Embryo well differentiated. Cotyledons 2. Embryo chlorophyllous, or achlorophyllous; straight, or curved. Seedling. Germination phanerocotylar, or cryptocotylar.
Physiology, biochemistry. Aluminium accumulation not found. Photosynthetic pathway: C3.
Geography, cytology, number of species. A genus of 20 species.