1. Lyonia mariana (L.) D. Don (staggerbush)

Neopieris mariana (L.) Britton

Pl. 375 k–m; Map 1641

Plants shrubs, colonial by rhizomes. Stems 0.5–2.0 m tall, the bark gray, shallowly furrowed, and usually shredding in thin, narrow strips. Twigs glabrous to sparsely short-hairy, reddish brown to brown, becoming gray with age, often developing small black spots, lines, or streaks, the winter buds conic to ovoid, with 2–6 overlapping scales. Leaves well spaced along the branches, short-petiolate. Leaf blades 3–10 cm long, 1–5 cm wide, narrowly to broadly elliptic, narrowed or tapered to a sharply pointed tip, narrowed or less commonly rounded at the base, the margins entire, slightly thickened, the upper surface glabrous to sparsely short-hairy along the main veins, the undersurface with scattered minute, brown dots (actually minute papillae), also sparsely to moderately short-hairy along the main veins. Inflorescences of loose umbellate clusters along and at the tips of leafless branches, the flower stalks 5–20 mm long, with minute bracts at the very base. Flowers actinomorphic, hypogynous, fragrant. Calyces deeply 5-lobed, 4–7 mm long, the lobes narrowly oblong-triangular to nearly linear, sharply pointed at the tip, minutely glandular and sometimes also sparsely hairy. Corollas cylindrical to urn-shaped, 7–14 mm long, shallowly 5-lobed, the lobes spreading to recurved at flowering, white or less commonly pinkish-tinged, the outer surface sparsely glandular. Stamens 10, not exserted, the filaments with a prominent S-shaped curve, broadened at the base, densely hairy, with 2 short spurs near the anther-filament junction, the anthers lacking tubes or awns at the tip, but with a white, powdery deposit on the dorsal surface, dehiscing by 2 terminal pores. Ovary superior, glabrous, concave at the tip, with 5 locules, the placentation axile. Style 5–6 mm long, straight, usually slightly exserted at flowering, the basal portion persistent at fruiting, the stigma capitate, slightly lobed. Fruits capsules 5–6 mm long, 4–5 mm wide, urn-shaped to pear-shaped, glabrous, brown with 5 thickened, pale brown ribs. Seeds 0.7–1.5 mm long, oblong-ovoid, somewhat angled, truncate at the tip, with a minute tail at the base, brown, the surface smooth. 2n=24. May–June.

Uncommon and perhaps extirpated, known thus far only from Dent County (eastern U.S. from New York to Florida, also Missouri to Louisiana west to Oklahoma and Texas). Mesic upland forests in ravines.

This species was first reported for Missouri by Kucera (1953). The Missouri population, which has not been seen for many years, is somewhat disjunct from the closest populations in north-central Arkansas. The central United States sites in turn are disjunct from the species distribution in the eastern states, where it grows primarily in the Atlantic Coastal Plain. The leaves of L. mariana contain a series of toxic diterpenoid compounds, including grayanotoxin (andromedotoxin) and lioniatoxin (Burrows and Tyrl, 2001), which are poisonous to humans and livestock. These can have an intoxicating narcotic effect on sheep and cattle, hence the common name staggerbush (Judd, 1981).

The pollination mechanism in Lyonia is unusual among Missouri plants, but it is characteristic of some other non-Missouri genera of Ericaceae. The S-shaped filaments act as springs, initially positioning the anthers with the apical pores oriented inward. When a bee or other insect visits a flower and inserts its proboscis to sample nectar that collects at the corolla base, the anthers are first pushed outward, but then they spring back, dusting the insect’s mouthparts with pollen. The stigma does not become receptive until after the pollen is shed (Judd, 1981).