7. Ligustrum L. (privet) (Yatskievych and Summers, 1991)

Plants shrubs (small trees elsewhere), sometimes evergreen or semi-evergreen. Trunks few to several, ascending, sometimes arched, the bark grayish brown to gray, thin, relatively smooth, but with raised leaf scars and lenticels. Twigs relatively slender, variously yellowish green to gray, brown, or nearly black, glabrous or hairy, more or less circular in cross-section, the leaf scars raised and the lenticels conspicuous and raised. Terminal buds ovoid to conic-ovoid, with scales that are sharply pointed at the tips, the axillary buds similar to the terminal ones, but smaller. Leaves opposite or occasionally subopposite, mostly short-petiolate, the petioles of the largest leaves 1–16 mm long. Leaf blades simple, 1–8 cm long, 0.5–2.5 cm wide, oblong-elliptic to elliptic, oblong-ovate, or less commonly lanceolate to ovate, angled or tapered (rarely rounded or shallowly notched) to the bluntly to sharply pointed tip, rounded or angled to broadly angled at the base, the margins entire (sometimes minutely hairy), the upper surface green to dark green, glabrous, the undersurface slightly lighter green to yellowish green, glabrous or hairy, often also inconspicuously gland-dotted. Inflorescences terminal, few- to more commonly many-flowered, variously ascending to spreading or nodding panicles (occasionally reduced and nearly racemose) 1.5–10 cm long developing after the leaves, the lower branch points with small, leaflike or scalelike bracts, the flowers mostly with slender stalks 1–5 mm long (occasionally some of them sessile), moderately but unpleasantly fragrant. Calyces truncate at the tip (unlobed or sometimes appearing slightly wavy) or with 4 very shallow lobes 1.5–2.0 mm long, the lobes irregular, blunt or toothlike. Corollas 4-lobed to about the midpoint or less, 5–12 mm long, trumpet-shaped, the lobes oblong to oblong-ovate, white or occasionally cream-colored. Style 1–2 mm long, with a pair of ascending branches at the tip or more frequently the fused stigmas appearing as a club-shaped mass. Fruits berrylike drupes, 5–8 mm long, globose to broadly ellipsoid, green to olive green, turning bluish black or black, glabrous, sometimes slightly glaucous. About 45 species, Europe, Africa, Asia south to Australia.

Many species are grown in cultivation for their foliage in hedges, as screens or as specimen plants. The heavily scented flowers of Ligustrum were described by Mabberley (1997) as having an unpleasant, ammonia-like or fishy smell (caused by methylamine) that reportedly can taint the honey of honeybees that visit the flowers. Species of Ligustrum are considered toxic to livestock and humans, but there are conflicting reports on how poisonous the various species may be. Terpenoid glycosides, especially ligustrin derivatives of oleanolic acid, are suspected as the chemical basis of intoxication (Burrows and Tyrl, 2001). Symptoms are mostly gastrointestinal, including stomach and intestinal irritation, vomiting, and diarrhea, but also may progress to paralysis of the limbs, fluid in the lungs, and rarely death.

Privets are popular in horticulture as background shrubs, windbreaks, hedges, and specimen plants. A number of other Ligustrum species in addition to those treated below are cultivated in the United States, including L. amurense Carrière (Amur privet), L. japonicum Thunb. (Japanese privet), L. lucidum W.T. Aiton (glossy privet), and L. quihoui Carrière (waxy-leaved privet). Cultivars are available with variegated leaves of green and white or green and yellow.

The inclusion by Steyermark (1963) of only L. ovalifolium and L. vulgare (as an excluded species) for the state has led to the misidentification of some Missouri specimens. Additional collections of naturalized plants are needed to more accurately determine the species occurring in the state and their respective distributions. Hardin (1974) and K. A. Wilson and Wood (1959) pointed to a need for further taxonomic work on the genus. The following key is adapted from Hardin’s work and requires flowering material for accurate determinations.