1. Ammi majus L. (bishop’s weed)
Pl. 202 a, b;
Map 838
Plants annual.
Stems 20–80 cm long, erect or ascending, glabrous. Leaves alternate and also
basal (basal rosette usually present at flowering), glabrous, short- to
long-petiolate, the sheathing bases not inflated. Leaf blades 2–20 cm long,
oblong to broadly triangular-ovate in outline, those of the basal and lowermost
stem leaves ternately or pinnately 1 time compound, the leaflets 10–20 mm long,
elliptic-lanceolate, narrowed at the base, rounded or narrowed to a sharp point
at the tip, finely toothed along the margins; the blades of the median and
upper stem leaves 2 times pinnately dissected, the ultimate segments 2–20 mm
long, narrowly linear, narrowed to sharply pointed tips. Inflorescences terminal
and sometimes also axillary, compound umbels, mostly long-stalked, the stalks
roughened. Involucre of numerous 1 or 2 times pinnately dissected bracts, these
mostly longer than the rays, spreading to reflexed at flowering, with thin,
papery margins and sharply pointed tips. Rays numerous, 2–7 cm long, roughened.
Involucel of numerous entire bractlets, these mostly slightly shorter than the
flower stalks, with thin, papery margins and sharply pointed tips. Flowers
mostly numerous in each umbellet, the stalks 3–12 mm long. Sepals minute
triangular teeth. Petals ovate to obovate, broadly rounded to more commonly
notched or 2-lobed at the tip, white. Ovaries glabrous. Fruits 1.5–2.5 mm long,
oblong-elliptic in outline, flattened laterally, glabrous, dark brown, each
mericarp with 5 shallow, angled ribs lacking wings. 2n=22. May–July.
Introduced,
known thus far only from the city of St. Louis (native of Europe, Asia; widely
cultivated as an ornamental, escaped sporadically in the U.S.). Railroads and open,
disturbed areas.
Plants of A.
majus, particularly the immature fruits, reportedly contain furanocoumarins
and related compounds similar to those found in Heracleum and may cause
phototoxic dermatitis in some individuals. The plants are sometimes grown for
the cut-flower trade or for use in dried flower arrangements.